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Temperature Changes over the CORDEX-MENA Domain in the 21st Century Using CMIP5 Data Downscaled with RegCM4: A Focus on the Arabian Peninsula

Temperature Changes over the CORDEX-MENA Domain in the 21st Century Using CMIP5 Data Downscaled... Hindawi Advances in Meteorology Volume 2019, Article ID 5395676, 18 pages https://doi.org/10.1155/2019/5395676 Research Article Temperature Changes over the CORDEX-MENA Domain in the st 21 Century Using CMIP5 Data Downscaled with RegCM4: A Focus on the Arabian Peninsula Mansour Almazroui Center of Excellence for Climate Change Research/Department of Meteorology, King Abdulaziz University, Jeddah 21589, Saudi Arabia Correspondence should be addressed to Mansour Almazroui; mansour@kau.edu.sa Received 25 December 2018; Revised 21 March 2019; Accepted 22 April 2019; Published 20 May 2019 Academic Editor: Jorge E. Gonzalez Copyright © 2019 Mansour Almazroui. )is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. )is paper examined the temperature changes from the COordinated Regional climate Downscaling Experiment (CORDEX) over st the Middle East and North Africa (MENA) domain called CORDEX-MENA. )e focus is on the Arabian Peninsula in the 21 century, using data from three Coupled Model Intercomparison Project Phase 5 (CMIP5) models downscaled by RegCM4, a regional climate model. )e analysis includes surface observations along with RegCM4 simulations and changes in threshold st based on extreme temperature at the end of the 21 century relative to the base period (1971–2000). Irrespective of the driving CMIP5 models, the RegCM4 simulations show enhanced future temperature changes for RCP8.5 as compared to RCP4.5. )e ° ° Arabian Peninsula will warm at a faster rate (0.83 C per decade) as compared to the entire domain (0.79 C per decade) for RCP8.5 ° ° during the period 2071–2100. Moreover, the number of hot days (T ≥ 50 C) (cold nights: T ≤ 5 C) will increase (decrease) max min faster in the Arabian Peninsula as compared to the entire domain. )is increase (decrease) of hot days (cold nights) will be more prominent in the far future (2071–2100) as compared to the near future (2021–2050) period. Moreover, the future changes in temperature over the main cities in Saudi Arabia are also projected. )e RegCM4-based temperature simulation data from two suitable CMIP5 models are recommended as a useful database for further climate-change-related studies. frequent heavy rainfall events occurred in Saudi Arabia over 1. Introduction the last decade and temperature often exceeded 50 C, and In the present era of climate change, a proper assessment of even reached 52 C in 2010 [2, 3]. Such events need to be vulnerable sectors is important in developing strategies for predicted because heavy rainfall events cause flash floods the adaptation and long-term planning by national policy- and high temperatures can cause heat strokes. Local people, makers and other stakeholders. In this regard, an accurate migrant populations, and the Pilgrims from all over the climate database is one of the main prerequisites for climate world, are all very vulnerable when exposed to these phe- change impacts studies, which remain scarce in the Arab nomena. In this connection, reliable climate projections, region, particularly in the Arabian Peninsula. )e climate of including increased utilization of climate model data, are the Arab region is generally governed by the synoptic-scale essential for the region. forcing (e.g., sea surface temperature, moisture, and wind) For the years 1956–2005, the Intergovernmental Panel coming from the Indian and Atlantic oceans, while the on Climate Change (IPCC) has reported a global warming Indian Ocean, the Mediterranean Sea, and Sudan low (low trend of 0.13 C/decade [4], and in the updated fifth as- pressure zone over East Africa) control the Arabian Pen- sessment report (AR5), it was updated to 0.12 C/decade for insula’s climate [1]. )e regional climate projection for the the period 1951–2012 [5]. )is global warming and Arabian Peninsula is a challenging task. For example, associated climate change undoubtedly has long-term 2 Advances in Meteorology no topographic information at finer scales. To overcome this consequences for many socioeconomic sectors, such as water consumption, power generation, human health, bio- problem, RCMs are considered to be the best tools for downscaling GCM-generated climatic features, to obtain diversity, and ecosystems. )ese may be contributory factors to the formation of certain atmospheric pollutants associ- more detailed climate information over a particular region ated with the rise in air temperature [6–8]. )e rise of air [23, 24]. RCMs are also invaluable over areas where ob- temperature is likely to lead to an increase in air pollutants servations are either scarce or absent, as over the Arab [9]. )e IPCC also projected a possible increase in frequency region. )e RCMs outperform the driving global climate and intensity of extreme temperatures over the Arabian models and provide added value to simulate the climate of a Peninsula [4]. In the coming decades, climate change could region [25]. )us, dynamic downscaling of GCM simula- have a significant impact on water supplies in many parts of tions has been a widely used and acceptable strategy [26, 27]. the globe and particularly in the semiarid/arid regions. In other words, an RCM can be used to generate future climate simulations as well as to help understand the past )erefore, these impacts might be more severe for the Arabian Peninsula, and in particular, for Saudi Arabia, climate in a particular region. )us, the climate variables generated by a suitable RCM can be used in extreme analysis which contains the world’s largest continuous sand desert, the Rub Al-Khali [2, 3, 10]. in the Arab region, focusing on the Arabian Peninsula In the temperature climatology of Saudi Arabia, the (particularly Saudi Arabia), for the projection period. northern side is colder than the southern side [11]. In the )erefore, this paper aimed to investigate the changes in ° ° ° extreme north, the temperature ranges from 8.57 C to temperature over the CORDEX-MENA domain (27 W–76 E ° ° ° 28.32 C through the different seasons, while it ranges from and 7 S–45 N) with a focus on the Arabian Peninsula during st ° ° 26.68 C to 33.97 C in the southern regions. )e ocean does the 21 century, by using data from three GCMs from not contribute to the rapid increase of temperature in the CMIP5 project downscaled with an RCM, namely, regional Arabian Peninsula as the ocean temperature increases more climate model system updated in 2010 (RegCM4). slowly than land temperature in the peninsula [12]. Changes )e CORDEX-MENA domain is defined using sensi- in the climate, and particularly changes in temperature, tivity tests from seven related domains. Details of the do- increase the risk of extreme events such as heat and cold main selection along with the reason for selecting this new waves, in addition to more frequent droughts and probable domain within the CORDEX framework are provided in drought intensification [13]. )e trends of annual and [28]. )e analysis is mainly focused over Saudi Arabia (about seasonal extreme indices over Saudi Arabia over recent 80% area of the Arabian Peninsula) which is a region with decades were studied by [14], who reported a warming trend scarce climate change studies. In order to understand the over the region. Moreover, climate change is likely to be the possible changes in temperature, the corrected temperature most dangerous threat to regional biodiversity [15]. is projected into the future. )is paper also aims to in- Moreover, the Arab region, and particularly the Arabian vestigate extreme temperatures using thresholds for warm Peninsula, is one of the most vulnerable areas to the po- and cold days from regional to local scales and validate with tential threats listed under the dry-land ecosystems [16]. ground stations across Saudi Arabia. Model-generated climatic information for both near and more distant future periods is required to assist with long- 2. Data and Methodology term planning. In this connection, a global climate model (GCM) is the only tool that can generate future climate [17]. 2.1. Model Description. )e regional climate model )e IPCC AR5 report used the Coupled Model In- (RegCM) is a limited-area model developed by the Abdus tercomparison Project Phase 5 (CMIP5) multimodel data- Salam International Centre for )eoretical Physics (ICTP), base developed under the World Climate Research Program. Trieste, Italy, for the purpose of long-term climate simu- Downscaling is usually used to transform the GCM outputs lation. )is model is used by a large community of re- into a more suitable form [18]. Dynamical downscaling is searchers to study regional climate, including over the based on physical models which are in fact the regional CORDEX-MENA domain (e.g., [17, 29]). Details about climate models (RCMs). Statistical downscaling is another RegCM version 4.3.4 (RegCM4) are available in [30]. procedure based on empirical nature where downscaled RegCM4 uses the dynamical core from [31] and the radi- projections remain constant over time [19]. It is used to ation scheme from [32, 33]. )e BATS (biosphere and at- project the climatic variables used by many researchers mosphere transfer scheme) from [34, 35] and the CLM (e.g., [18, 20, 21]). )ere are advantages and disadvantages in (community land model) from [36] are also used. )e PBL both dynamical and statistical downscaling procedures. )e (planetary boundary layer) and ocean fluxes are from statistical downscaling is cheaper and consumes less com- [37, 38], respectively. puting resources [18]. Because our aim is to understand the Multiple cumulus convection schemes are available climate variability, the use of dynamical downscaling is within RegCM4. Among them, the schemes in [39, 40] and preferred for this analysis where physical parameterization Arakawa–Schubert schemes are assimilated into the more can be selected for optimized results. )e CMIP5 GCMs are general Grell convection parameterization scheme. )e generally coarse resolution (100–300 km) models and are not combination of Grell and Emanuel [28], or either of them suitable for generating detailed climatic conditions over a uniquely, can be used for land and ocean masking. In the specific region [22]. GCMs cannot simulate the detailed present study, the European Centre for Medium-Range structure of regional climatic phenomena because they have Weather Forecasts (ECMWF) Reanalysis (ERA-Interim, Advances in Meteorology 3 ° ° hereafter refereed as ERA-Int) 0.75 × 0.75 gridded 6-hourly simulated temperature data were extracted for 11 sub- data (http://www.ecmwf.int/products/data/archive) are used domains within the entire domain (Figure 1), as well as for to provide initial conditions for three CMIP5 model sim- the 27 meteorological station locations across Saudi Arabia. ulations of both past and future climate. RegCM4 is forced )e ground-truth station data were collected from the by ERSST, the extended reconstructed sea surface temper- General Authority of Meteorology and Environmental ature data. )e Coordinated Regional climate Downscaling Protection (GAMEP). )e data extraction near the grid Experiment (CORDEX) recommended use of RegCM4 at point of each meteorological station was done as in [45, 46]. 50 km resolution, as used in this study, though it may also be In this procedure, the station data are interpolated from the used at higher resolutions [28]. nearest points of a grid to where the station is located. Details of how the 11 subdomains adopted in this study were selected are available in [28, 29], and the characteristics 2.2. Experimental Setup. )ree CMIP5 models, namely, the of the 27 meteorological stations may be found in [2, 3]. )e HadGEM2 (the UK Met Office Hadley Centre Global En- extracted data are processed on daily, monthly, and annual ° ° vironment Model version 2, 1.2 ×1.8 [41]); CanESM (the time scales and objectively compared with the observed/ Canadian Earth System Model of the Canadian Centre for gridded datasets over the same temporal scale. Regression ° ° Climate Modeling and Analysis (CCCma), 2.8 × 2.8 [42]; coefficients are obtained for temperature (mean, maximum, and ECHAM6 (Atmospheric GCM of Max Planck Institute and minimum) of both observed and RegCM4 datasets. )e ° ° for Meteorology, Germany, 1.8 ×1.8 [43]), are used for the relative temperature is calculated as each time series minus past climate study. In addition, two representative con- the 1971–2000 average of each source. As in [28], the better centration pathways (RCPs), i.e., RCP4.5 and RCP8.5 are land-surface option within RegCM4 is selected for each used for the future climate projections. )e use of subdomain and for the entire domain. For this purpose, HadGEM2, CanESM, and ECHAM6 is based on [28]. An statistical measures such as mean, bias, correlation (r), root additional simulation of past climate has also been carried mean square difference (RMSD), and standard deviation out using ERA-Int reanalysis as the input in RegCM4. As (Std) against CRU values are used. mentioned above, the RCM domain extending from 7 S to Daily data are used to analyze extreme temperatures ° ° ° 45 N and 27 W to 76 E encompasses the Arab region and is such as hot days and cold nights with a certain threshold adopted from [28]. )is domain is sufficiently large for RCM temperature. In this analysis, hot days and cold nights are simulations and is known as the CORDEX-MENA domain defined as those with maximum temperature greater than or (see [28]). )is domain was obtained from seven sensitivity ° ° equal to 50 C (T ≥ 50 C) and minimum temperature less max experiments, and it fits well with the CORDEX Arab do- ° ° than or equal to 5 C (T ≤ 5 C), respectively. )e change in min main. Results of the sensitivity experiments (not shown hot days and cold nights was calculated as the number of here) indicate a better performance of the land surface days/nights in a projected year minus the average number of scheme BATS (not CLM) for the analysis domain [28]. )is days/nights over the base period. As given in [12], simple study follows the recommendation in [29] to use the Grell regression methods were employed for trend analysis, while convection scheme over land and the Emanuel scheme over trend significance was assessed using the F-test. )e pro- the ocean within the analysis domain. jected temperature was obtained from six simulations (listed Prior to starting the long run of the historical and future in Table 1) for the entire domain and each subdomain, for climates, a number of sensitivity experiments (spanning both near and far future periods, using RCP4.5 and RCP8.5 2000–2005) were completed with different convective pa- scenarios. Finally, the future changes in temperature were rameterization schemes, domains, and land surface schemes computed for both the near and far future periods with in order to select the best domain, the most suitable con- respect to the past climate. )e corrected temperature was vection scheme, and the best land surface scheme (see obtained by adding the base period (1971–2000) bias to the [17, 28, 29]). Later on, a total of 10 simulations were per- projected temperature, and the future climate anomaly was formed using the optimal settings of RegCM4.6 model, as obtained by subtracting the average from each time series. listed in Table 1. All simulations for this study using RegCM4.6 were performed at 50 km resolution in a single 3. Results and Discussion domain without further nesting. 3.1. Past Climate Temperature. )e mean air temperature 2.3. Analysis Procedures. )e interannual variability of (at 2 m) averaged over all subdomains (i.e., CORDEX) in- simulated air temperature (2 m) for the entire domain and a dicates that model-simulated values correspond well with the subdomain over the Arabian Peninsula was compared with observations over the annual cycle (Figure 2(a)). However, observations of the past climate (1971–2000) from the there is a little underestimation by RegCM4-HadGEM2 Climatic Research Unit (CRU) dataset [44]. Simulated (−1.17 to −2.62 C w.r.t. CRU) and RegCM4-ECHAM6 temperature biases (model minus observation) were also (−0.91 to −1.91 C w.r.t. CRU) as compared to the CRU calculated with the CRU data. )e CRU gridded dataset has a and ERA-Int data, while there is very large overestimation by ° ° ° spatial resolution of 0.5 , the same as the RegCM4 runs. RegCM4-CanESM (6.95 C to 11.63 C w.r.t. CRU). Similar Changes in temperature were generated for two future behavior in the mean temperature is also present in the in- periods, the near future (2021–2050) and the far future dividual subdomains, such as the subdomain over the Arabian (2071–2100), relative to the base period. )e RegCM4- Peninsula (Figure 2(b)). In this subdomain, ERA-Int also 4 Advances in Meteorology Table 1: List of simulations performed in this study. No. Simulation name Simulation period Boundary conditions RCPs 1 RegCM4-ERA-Int 1979–2015 ERA-Interim – 2 RegCM4-HadGEM2 1960–2005 HadGEM2 hist 3 RegCM4-CanESM 1960–2005 CanESM hist 4 RegCM4-ECHAM6 1960–2005 ECHAM6 hist 5 RegCM4-HadGEM2 2006–2100 HadGEM2 RCP4.5 6 RegCM4-CanESM 2006–2100 CanESM RCP4.5 7 RegCM4-ECHAM6 2006–2100 ECHAM6 RCP4.5 8 RegCM4-HadGEM2 2006–2100 HadGEM2 RCP8.5 9 RegCM4-CanESM 2006–2100 CanESM RCP8.5 10 RegCM4-ECHAM6 2006–2100 ECHAM6 RCP8.5 45°N averages from RegCM4-HadGEM2 and RegCM4-ECHAM6 40 °N 3500 were used in the rest of the analysis. 35 °N 3000 Spatial distributions of mean temperature obtained from 30 °N CRU and RegCM4-ERA-Int show similar patterns of an- 25 °N 2000 nual, winter, and summer temperatures (Sup 1). At annual 20 °N scale, the temperature in the latitudinal band from 5–25 N is 15 °N ° 1000 slightly too high and is relatively higher to the south of 15 N 10 °N 500 during the winter season. )e highest temperature is ob- 5°N 100 served in the band from 15–35 N in the summer season. EQ 10 Spatial distributions of simulated temperature bias for 5°S the two CMIP5 models downscaled using RegCM4 show that the RegCM4-HadGEM2 and RegCM4-ECHAM6 underestimate temperature relative to CRU observations Figure 1: Analysis domain with 11 subdomains. )e subdomain A at both annual and seasonal scales (Figure 3). Quantifying is over the Arabian Peninsula which is focused in this analysis for the temperature bias (model minus observation), the un- detail study. )e elevation (in meters) indicates the topography of derestimation by RegCM4-HadGEM2 and RegCM4- the domain. ° ° ECHAM6 is about 2 C to 3 C for most of the domain at annual scale (Figures 3(a) and 3(b)). )ere is a dipole underestimates (−0.51 to −2.54 C) mean temperature com- anomaly in the RegCM4-simulated temperature distribu- pared to the CRU data. Note that CRU is the observed data tion over the Arabian Peninsula: the overestimation (un- gridded over the region while ERA-Int is the reanalysis data derestimation) or positive (negative) bias over southeast generated using the assimilation system. In the case of (northwest) Arabian Peninsula for RegCM4-HadGEM2 RegCM4-ECHAM6, the underestimation (−0.92 to −1.14 C) and RegCM4-ECHAM6. )is dipole anomaly in the dis- occurs mostly during the winter months, while for RegCM4- tribution of temperature in two different areas is most HadGEM2, the underestimation occurs all year round. For obvious in the summer season (JJA; Figures 3(e) and 3(f)) RegCM4-CanESM, the large overestimation is for all months as compared to the winter season (DJF) (Figures 3(c) and 3(d)). during the year. During the summer months, the over- ° ° estimation by RegCM4-CanESM can reach above 10 C In the summer months, warm bias exceeds 7 C over ° ° (11.04 C to 11.90 C). )e temperature annual cycle for both Yemen/Oman for the RegCM4 simulations, while studies the CORDEX domain and the Arabian Peninsula subdomain [17, 29] report that it exceeds 8 C for the dry season months shows underestimation (e.g., RegCM4-HadGEM2 and (JJAS). A similar large bias in the ERA-40 and ECHAM5 RegCM4-ECHAM6) by some models and overestimation driving fields, compared to RegCM3 simulations of annual (e.g. RegCM4-CanESM) by the other, relative to the tem- temperature over this region, particularly over the south- perature climatology. )e temporal evolution of the relative western Arabian Peninsula, has also been reported by [25]. temperature (i.e., each time series minus the 1971–2000 av- )ey concluded that RegCM usually simulates lower tem- erage of each source) for the entire domain and Arabian peratures than the forcing data; i.e., RegCM3 reduced the Peninsula subdomain (Figures 2(c) and 2(d)) indicates that warm bias that was seen in the HadGEM2- and ECHAM6- there is an increase in temperature over time for all time driven runs. series. )e 10-year moving average indicates a clear trend in Over the entire domain, RegCM4-CanESM simulates the relative temporal evolution. In this analysis, RegCM4- higher temperatures than observed by CRU and ERA-Int, CanESM overestimated the temperature more than 10 C; an while RegCM4-HadGEM2 and RegCM4-ECHAM6 simu- overestimation of about 8 C was also reported by [28]. Be- late slight lower temperatures (Figure 4). For the entire cause we use the same RegCM4 to downscale the CMIP5 domain, RegCM4-HadGEM2 (RegCM4-ECHAM6) un- ° ° models, the large overestimation in RegCM4-CanESM may derestimates temperature by 1.93 C (1.36 C) (Figure 4(a)). be transformed from the global climate model. )erefore, A similar situation is also noticed for the Arabian Pen- RegCM4-CanESM was not considered further, and only insula subdomain. In this subdomain, the temperature 21 °W 14 °W 7°W 7°E 14 °E 21 °E 28 °E 35 °E 42 °E 49 °E 56 °E 63 °E 70 °E Advances in Meteorology 5 45 45 40 40 35 35 30 30 25 25 20 20 15 15 10 10 5 5 0 0 CRU ERA-Int CRU ERA-Int RegCM4-HadGEM RegCM4-ECHAM RegCM4-ECHAM RegCM4-HadGEM RegCM4-CanESM RegCM4-CanESM (a) (b) 2.10 2.10 1.60 1.60 1.10 1.10 0.60 0.60 0.10 0.10 –0.40 –0.40 –0.90 –0.90 –1.40 –1.40 10-year moving average CRU 10-year moving average CRU (CRU) (CRU) ERA–Int 10-year moving average ERA–Int 10-year moving average (RegCM4–HadGEM) (RegCM4–HadGEM) RegCM4–HadGEM 10-year moving average RegCM4–HadGEM 10-year moving average (RegCM4–ECHAM) (RegCM4–ECHAM) RegCM4–ECHAM 10-year moving average RegCM4–ECHAM 10-year moving average (RegCM4–CanESM) (RegCM4–CanESM) RegCM4–CanESM RegCM4–CanESM (c) (d) Figure 2: Annual cycle average temperature for (a) CORDEX-MENA/Arab domain and (b) Arabian Peninsula subdomain for the present climate 1971–2005. Temporal evolution for the relative temperature (each time series minus the 1971–2000 average of each source) for (c) CORDEX-MENA/Arab domain and (d) Arabian Peninsula subdomain. ° ° underestimations are 1.83 C and 4.43 C, by RegCM4- compared for two scenarios and three CMIP5 models HadGEM2 and RegCM4-ECHAM6, respectively, with (Figure 5). )e mean temperature for each CMIP5 model reference to the CRU data (Figure 4(b)). )e bias may come and two RCPs for the near and far future averaged over 11 from the RegCM4 itself for its parameterization or may be subdomains of the entire domain, and the Arabian from the inherent to the CMIP5 modeling systems. Peninsula subdomain, indicates that both RegCM4- HadGEM2 and RegCM4-ECHAM6 simulate nearly sim- ilar temperature (Figure 5). For RCP8.5, the average from 3.2. Projected Changes in Temperature. Before analyzing the RegCM4-HadGEM2 and RegCM4-ECHAM6 is 25.03 C ° ° ° changes in future temperature, the RegCM4-simulated (23.66 C) for the near future and 28.69 C (27.27 C) for the temperatures for the near and far future periods are far future, over the entire domain (Arabian Peninsula Temperature anomaly (°C) Temperature (°C) JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV 2003 DEC Temperature anomaly (°C) Temperature (°C) JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 2003 6 Advances in Meteorology 45°N 45°N 40°N 40°N 35°N 35°N 30°N 30°N 25°N 25°N 20°N 20°N 15°N 15°N 10°N 10°N 5°N 5°N EQ EQ 5°S 5°S C C –7 –6 –5 –4 –3 –2 –1 –0.5 0.5 1234567 –7 –6 –5 –4 –3 –2 –1 –0.5 0.5 1234567 (a) (b) 45°N 45°N 40°N 40°N 35°N 35°N 30°N 30°N 25°N 25°N 20°N 20°N 15°N 15°N 10°N 10°N 5°N 5°N EQ EQ 5°S 5°S C C –7 –6 –5 –4 –3 –2 –1 –0.5 0.5 1234567 –7 –6 –5 –4 –3 –2 –1 –0.5 0.5 1234567 (c) (d) 45°N 45°N 40°N 40°N 35°N 35°N 30°N 30°N 25°N 25°N 20°N 20°N 15°N 15°N 10°N 10°N 5°N 5°N EQ EQ 5°S 5°S C C –7 –6 –5 –4 –3 –2 –1 –0.5 0.5 1234567 –7 –6 –5 –4 –3 –2 –1 –0.5 0.5 1234567 (e) (f) Figure 3: Spatial distribution of air temperature bias (in C) with respect to CRU data for (a) annual RegCM4-HadGEM2, (b) annual RegCM4-ECHAM6, (c) winter RegCM4-HadGEM2, (d) winter RegCM4-ECHAM6, (e) summer RegCM4-HadGEM2, and (f) summer RegCM4-ECHAM6 averaged over the common period 1971–2000. subdomain). In this case, the standard deviation is 0.55 0.38 (0.38) for the near future and 0.36 (0.46) for the far (0.58) for the near future and 0.77 (0.90) for the far future future over the entire domain (Arabian Peninsula sub- over the entire domain (Arabian Peninsula subdomain). domain). )is clearly indicates that the RCP8.5 simulates For RCP4.5, the projected temperature is 24.67 C higher temperatures with larger standard deviations as ° ° ° (23.30 C) and 26.02 C (24.74 C) for the near and far fu- compared to the RCP4.5, particularly in the far future. ture, respectively, over the entire domain (Arabian Pen- Note that the past temperature for the entire domain from ° ° ° insula subdomain). In this case, the standard deviation is CRU (ERA-Int) is 24.49 C (24.34 C) and is 22.56 C and 21°W 21°W 21°W 14°W 14°W 14°W 7°W 7°W 7°W 0 0 0 7°E 7°E 7°E 14°E 14°E 14°E 21°E 21°E 21°E 28°E 28°E 28°E 35°E 35°E 35°E 42°E 42°E 42°E 49°E 49°E 49°E 56°E 56°E 56°E 63°E 63°E 63°E 70°E 70°E 70°E 21°W 21°W 21°W 14°W 14°W 14°W 7°W 7°W 7°W 0 0 0 7°E 7°E 7°E 14°E 14°E 14°E 21°E 21°E 21°E 28°E 28°E 28°E 35°E 35°E 35°E 42°E 42°E 42°E 49°E 49°E 49°E 56°E 56°E 56°E 63°E 63°E 63°E 70°E 70°E 70°E Advances in Meteorology 7 25 25 20 20 15 15 (a) (b) Figure 4: Box plots of RegCM4-simulated air temperature (in C) for each model for the past climate averaged over (a) 11 subdomains for the CORDEX-MENA/Arab domain and (b) subdomain over the Arabian Peninsula. )e temperature is averaged over the period 1980–2005. 23.13 C for the HadGEM2- and ECHAM6-driven runs, average from the beginning of the 2040s, for both RCP4.5 respectively (see Figure 4). Over the Arabian Peninsula and RCP8.5 (Figure 6). )e temperature anomaly was ob- ° ° subdomain, these values are 25.33 C (23.50 C) for CRU tained by adding the base period bias to the projection ° ° (ERA-Int) and 20.90 C and 22.39 C for HadGEM2- and period (hence called the corrected temperature) and then ECHAM6-driven runs, respectively. subtracting the average from each year. Irrespective of the For the RCP4.5 scenario, future changes in the simulated driving model, the RCP8.5 projected higher temperatures mean temperature (averaged from RegCM4-HadGEM2 and than RCP4.5 did. )e difference between RCP4.5 and RegCM4-ECHAM6) indicate a rise in the annual mean of RCP8.5 in the base period is due to the anomaly calculation around 2 C in the near future over the full domain, which (yearly value minus the average from 2071–2100) though the will accelerate to 4 C over the Arabian Peninsula in the far data for both scenarios are exactly the same for this period. future (Sup 2(a) and 2(b)). In the winter season, the pro- )e spread is for the daily average to obtain an annual value ° ° jected change in temperature will reach about 3 C (4 C) for for the different driving GCMs. Averages from RegCM4- HadGEM2 and RegCM4-ECHAM6 over the entire domain the near (far) future over the peninsula (Sup 2(c) and 2(d)). In the summer season, the rise in temperature will not indicate that temperature will increase significantly (at 95% ° ° ° exceed 2.5 (3.5 C) in the near (far) future over the Arabian level) at the rate of 0.73 (0.27), 0.59 (0.39), and 0.79 (0.20) C Peninsula (Sup 2(e) and 2(f)). Hence, the average data show per decade for RCP8.5 (RCP 4.5) during the periods a larger increase in the winter season temperature compared 2021–2100, 2021–2050, and 2071–2100, respectively. A to the summer season. similar increasing trend in temperature is projected for the For the RCP8.5 scenario, future changes in the simulated Arabian Peninsula subdomain. )e rate of increase in mean temperature (averaged from RegCM4-HadGEM2 and temperature for this subdomain is projected to be 0.72 RegCM4-ECHAM6) indicate a rise in the annual mean of (0.29), 0.60 (0.30), and 0.83 (0.25) C per decade for RCP8.5 ° ° around 2.5 C in the near future, which will accelerate to 6 C (RCP4.5) during the periods 2021–2100, 2021–2050, and over the Arabian Peninsula in the far future (Sup 3(a) and 2071–2100, respectively, which are significant at 95% level. 3(b)). For the same regions, the future change in temperature Hence, the rising trend in temperature for the RCP8.5 ° ° will reach about 4 C (7 C) for the near (far) future periods scenario in the far future is higher for the subdomain over during the winter season (Sup 3(c) and 3(d)). In the summer the Arabian Peninsula than over the entire domain because season, the rise in temperature over the Arabian Peninsula will the averaging filters out the peak temperatures in the entire be within 7 C (Sup 3(e) and 3(f)). Average data show a larger domain. )ese projected changes in temperature are useful increase in the winter season temperature compared to the in climate change impact studies and vulnerability, adap- summer season. )ese results support the statement that the tation (e.g., [48]) and drought studies (e.g., [49–51]). environment is warming while cold extremes warm faster than warm extremes by about 30 to 40% globally averaged [47]. Future changes in mean temperature (averaged over all 3.3. Hot Days and Cold Nights. )e projected number of subdomains) indicate that it will be above the 1971–2100 RegCM4-simulated hot days (T ≥ 50 C) is large in the max Temperature (°C) CRU RegCM4-ERA-Int RegCM4-HadGEM RegCM4-ECHAM Temperature (°C) CRU RegCM4-ERA-Int RegCM4-HadGEM RegCM4-ECHAM 8 Advances in Meteorology 35 35 30 30 25 25 20 20 (a) (b) 35 35 30 30 25 25 20 20 (c) (d) Figure 5: Box plots of RegCM4-simulated air temperature (in C) for each model and RCPs for near future and far future averaged over 11 subdomains for CORDEX-MENA/Arab domain (a, b) and subdomain over the Arabian Peninsula (c, d). )e Ens2RCP8.5 and EnsRCP4.5 represent the average from HadGEM and ECHAM for the RCP8.5 and RCP4.5, respectively. )e red boxes are for RCP8.5 and yellow boxes for RCP4.5. eastern region of the Arabian Peninsula and may reach in the far future. )ese results support previous studies about 120 days with RCP4.5 in the near future and above (e.g., [29]) which found that warming over the Arabian 130 days in the far future (Figures 7(a) and 7(b)). )e dis- Peninsula increased in the future and is larger for the RCP8.5 tribution pattern of hot days for the RCP8.5 case is very scenarios than for RCP4.5. )e European and African re- similar to the RCP4.5 case for the near future (Figure 7(c)). gions also show a decrease of cold nights in the far future and However, the area covered by more than 130 hot days in- a greater decrease for RCP8.5 than for RCP4.5, which in fact creased during the far future (Figure 7(d)). Within the indicates the warming. )e number of hot days is relatively low for RCP4.5 and analysis domain, the number of hot days will increase for the European regions in the far future and the greater increase large for RCP8.5, when averaged from RegCM4-HadGEM2 will be under the RCP8.5 scenario as compared to RCP4.5. and RegCM4-ECHAM6 for both the CORDEX domain and )e distribution pattern of cold nights (T ≤ 5 C) is almost the Arabian Peninsula subdomain (Figure 8). An increase in min opposite to the pattern for hot days (Figures 7(e)–7(h)). In hot days is projected after the 2040s and will be large for the this case, more cold nights are projected in the western Arabian Peninsula subdomain as compared to the CORDEX region of the Arabian Peninsula and the number of cold domain. For the entire domain, the rate of increase rate in nights is larger with RCP4.5 than with RCP8.5. In addition, a hot days is 1.19 and 8.01 days per decade for the RCP4.5 and higher cold night number is observed in the near future than RCP8.5 scenarios, respectively, during the period 2021– Temperature (°C) Temperature (°C) HadGEM8.5 HadGEM8.5 ECHAM8.5 ECHAM8.5 Ens2RCP8.5 Ens2RCP8.5 HadGEM4.5 HadGEM4.5 ECHAM4.5 ECHAM4.5 Ens2RCP4.5 Ens2RCP4.5 Temperature (°C) Temperature (°C) HadGEM8.5 HadGEM8.5 ECHAM8.5 ECHAM8.5 Ens2RCP8.5 Ens2RCP8.5 HadGEM4.5 HadGEM4.5 ECHAM4.5 ECHAM4.5 Ens2RCP4.5 Ens2RCP4.5 Advances in Meteorology 9 –2 –4 –6 RCP8.5 HadGEM&ECHAM6 RCP8.5 RCP4.5 HadGEM&ECHAM6 RCP4.5 (a) –2 –4 –6 RCP8.5 HadGEM&ECHAM6 RCP8.5 HadGEM&ECHAM6 RCP4.5 RCP4.5 (b) Figure 6: Changes in corrected temperature (base period temperature bias is added with each yearly value) for (a) CORDEX-MENA/Arab and (b) Arabian Peninsula subdomain for the period 1971–2100. Anomaly is obtained from any yearly value minus the average amount. Average is obtained from HadGEM2- and ECHAM6-driven runs for both RCP4.5 and RCP8.5. Shaded area shows the range and gray color indicates the past climate. 2100. For the Arabian Peninsula subdomain, the RCP4.5 decade) scenarios, while the rate of decrease is greater for (RCP8.5) projected hot days will increase at the rate of the Arabian Peninsula subdomain (−3.49 and −6.14 days 1.57 (11.40) days per decade. All the trends in numbers of per decade for RCP4.5 and RCP8.5, respectively) for the hot days are statistically significant at the 95% level. Note period 2021–2100 (Figure 9). All the decreasing trends are that the ERA-Int-driven data available for the period statistically significant at 95% level. )e decrease of cold 1979–2015 support the pattern of hot days obtained from nights means the warming which may relate to the climate RegCM4-HadGEM2 and RegCM4-ECHAM6. change in the region. For the cold nights, the average For the entire domain, there is a downward trend in the pattern from the HadGEM2- and ECHAM6-driven runs number of RegCM4-simulated cold nights for both RCP4.5 closely follows the pattern from the ERA-Int-driven run (−1.52 days per decade) and RCP8.5 (−2.95 days per during the available period. Temperature anomaly (°C) Temperature anomaly (°C) 1971 1971 1974 1974 1977 1977 1980 1980 1983 1983 1986 1986 1989 1989 1992 1992 1995 1995 1998 1998 2001 2001 2004 2004 2007 2007 2010 2010 2013 2013 2016 2016 2019 2019 2022 2022 2025 2025 2028 2028 2031 2031 2034 2034 2037 2037 2040 2040 2043 2043 2046 2046 2049 2049 2052 2052 2055 2055 2058 2058 2061 2061 2064 2064 2067 2067 2070 2070 2073 2073 2076 2076 2079 2079 2082 2082 2085 2085 2088 2088 2091 2091 2094 2094 2097 2097 2100 2100 10 Advances in Meteorology 45°N 45°N 130 130 40°N 40°N 120 120 110 110 35°N 35°N 100 100 30°N 30°N 90 90 25°N 25°N 80 80 70 70 20°N 20°N 60 60 15°N 15°N 50 50 10°N 40 10°N 40 30 30 5°N 5°N 20 20 EQ EQ 10 10 5°S 1 5°S 1 (a) (b) 45°N 45°N 130 130 40°N 120 40°N 120 110 110 35°N 35°N 100 100 30°N 30°N 90 90 25°N 80 25°N 80 70 70 20°N 20°N 60 60 15°N 15°N 50 50 10°N 40 10°N 40 30 30 5°N 5°N 20 20 EQ EQ 10 10 5°S 5°S 1 1 (c) (d) 45°N 45°N 130 130 40°N 40°N 120 120 110 110 35°N 35°N 100 100 30°N 30°N 90 90 25°N 25°N 80 80 70 70 20°N 20°N 60 60 15°N 15°N 50 50 10°N 10°N 40 40 30 30 5°N 5°N 20 20 EQ EQ 10 10 5°S 5°S 1 1 (e) (f) 45°N 45°N 130 130 40°N 40°N 120 120 110 110 35°N 35°N 100 100 30°N 30°N 90 90 25°N 25°N 80 80 70 70 20°N 20°N 60 60 15°N 15°N 50 50 10°N 10°N 40 40 30 30 5°N 5°N 20 20 EQ EQ 10 10 5°S 5°S 1 1 (g) (h) Figure 7: Spatial distribution of RegCM4-simulated hot days (T > 50 C) for (a) RCP4.5 near future, (b) RCP4.5 far future, (c) RCP8.5 max near future, and (d) RCP8.5 far future along with cold nights (T < 5 C) for (e) RCP4.5 near future, (f) RCP4.5 far future, (g) RCP8.5 near min future, and (h) RCP8.5 far future. Average is taken over HadGEM2- and ECHAM6-driven runs. )e near and future is 2021–2050 and 2071–2100, respectively. 21°W 21°W 21°W 21°W 14°W 14°W 14°W 14°W 7°W 7°W 7°W 7°W 0 0 0 0 7°E 7°E 7°E 7°E 14°E 14°E 14°E 14°E 21°E 21°E 21°E 21°E 28°E 28°E 28°E 28°E 35°E 35°E 35°E 35°E 42°E 42°E 42°E 42°E 49°E 49°E 49°E 49°E 56°E 56°E 56°E 56°E 63°E 63°E 63°E 63°E 70°E 70°E 70°E 70°E 21°W 21°W 21°W 21°W 14°W 14°W 14°W 14°W 7°W 7°W 7°W 7°W 0 0 0 0 7°E 7°E 7°E 7°E 14°E 14°E 14°E 14°E 21°E 21°E 21°E 21°E 28°E 28°E 28°E 28°E 35°E 35°E 35°E 35°E 42°E 42°E 42°E 42°E 49°E 49°E 49°E 49°E 56°E 56°E 56°E 56°E 63°E 63°E 63°E 63°E 70°E 70°E 70°E 70°E Advances in Meteorology 11 100 100 90 90 80 80 70 70 60 60 50 50 40 40 30 30 20 20 10 10 0 0 RCP4.5 RCP4.5 Had and ECHAM Had and ECHAM ERA-Int75 ERA-Int75 (a) (b) 100 100 90 90 80 80 70 70 60 60 50 50 40 40 30 30 10 10 RCP8.5 RCP8.5 Had and ECHAM Had and ECHAM ERA-Int75 ERA-Int75 (c) (d) Figure 8: Number of RegCM-simulated hot days (T ≥ 50 C) for (a) CORDEX domain with RCP4.5, (b) Arabian Peninsula subdomain max with RCP4.5, (c) CORDEX domain with RCP8.5, and (d) Arabian Peninsula subdomain with RCP8.5. Average is taken from HadGEM2- and ECHAM6-driven runs. Shaded area shows the range, and gray color indicates the past climate. 3.4. Projected Changes in Hot Days and Cold Nights. Average values from RegCM4-HadGEM2 and RegCM4- Changes in hot days and cold nights using RegCM4-driven ECHAM6 indicate an increasing (decreasing) number of hot by HadGEM2 and ECHAM6, and obtained for future cli- days (cold nights) over both the CORDEX domain and the mates relative to the base period, are shown in Figure 10. )e Arabian Peninsula (Figures 7 and 8). Decadal analysis in- number of hot days will rise to about 50 days more in the dicates that the number of hot days is 568 (706) in the decade desert region (Rub Al-Khali) over the Arabian Peninsula in 2091–2100 as compared to only 15 (184) in the decade the near future, with respect to the base period. )is will 2021–2030 for the entire domain (Arabian Peninsula sub- reach about 80 days more in the far future for the RCP4.5 domain) with RCP8.5 (Figure 11(a)). Decadal analysis also scenario (Figures 10(a) and 10(b)). In the case of the RCP8.5 displays a decreasing number of cold nights in the last scenario, the number of hot days will reach about 70 days decade (CORDEX/Arabian Peninsula, −310/−675) as more in the desert region (Rub Al-Khali) over the Arabian compared to the earlier decade (CORDEX/Arabian Penin- Peninsula in the near future, with respect to the base period. sula, −118/−278). Note that the values are negative, so an )is will rise to about 130 days more in the far future increased negative value means a decrease in the number of st (Figures 10(c) and 10(d)). At the end of the 21 century, over cold nights. )e rate of decrease over the Arabian Peninsula most parts of the Arabian Peninsula, the number of hot days is higher than that over the entire domain (Figure 11(b)). will be about 60 days more compared to the base period, )ese results further indicate a higher warming rate over the Arabian Peninsula as compared to the entire domain during although in the southwest hilly region, the projected number st is small. )e number of cold nights is expected to drop by a the 21 century. large amount in the northwest and by a smaller amount in the southeast areas of the Peninsula. )e rate of decrease of cold nights will be large in the far future as compared to the 3.5. Maximum Temperature at Some Major Cities in Saudi Arabia. From the above discussion, it is evident that the near future for both RCPs (Figures 10(e)–10(h)). Hence, the st northwest region of the Peninsula will face great warming, future climate over the Arabian Peninsula during the 21 century will be warming at a higher rate as compared to the due to the faster rate of decrease of cold nights at the end of st the 21 century. entire domain. To understand the real pattern of Frequency (days) Frequency (days) 1971 1972 1981 1982 1986 1987 1991 1992 1996 1997 2001 2002 2006 2007 2011 2012 2016 2017 2031 2032 Frequency (days) Frequency (days) 1961 1961 1966 1966 1971 1971 1986 1986 1991 1991 2006 2006 2096 12 Advances in Meteorology 100 100 90 90 80 80 70 70 60 60 50 50 40 40 30 30 20 20 10 10 0 0 RCP4.5 RCP4.5 Had and ECHAM Had and ECHAM ERA-Int ERA-Int (a) (b) 100 100 90 90 80 80 70 70 60 60 50 50 40 40 30 30 20 20 0 0 RCP8.5 RCP8.5 Had and ECHAM Had and ECHAM ERA-Int ERA-Int (c) (d) Figure 9: Number of RegCM-simulated cold nights (T ≤ 5 C) for (a) CORDEX domain with RCP4.5, (b) Arabian Peninsula subdomain min with RCP4.5, (c) CORDEX domain with RCP8.5, and (d) Arabian Peninsula subdomain with RCP8.5. Average is taken from HadGEM2- and ECHAM6-driven runs. Shaded area shows the range, and gray color indicates the past climate. temperature rise over the Arabian Peninsula, the RegCM4- 33.81 C from the RegCM4 simulation. In the case of Riyadh, simulated maximum temperature are extracted at 27 average temperature over the common period of 1985–2014 is ° ° meteorological station locations across Saudi Arabia (80% 33.29 C (36.75 C) from observations (ERA-Int), while it is coverage of the Peninsula) and compared with the me- 34.90 C from the RegCM4 simulation. Overall, the simulation teorological station data. )is exercise gives us confidence underestimates the maximum temperature for Makkah and in the performance of RegCM4 for the simulation of Madinah while overestimating it for Riyadh and for the temperature over the study region. Note that data available country as a whole, relative to the surface observations. )is from just one station in each city are taken as represen- indicates regional variations in temperature simulation using tative of the city for the purposes of this study. RegCM4 which depends on different factors including land )e patterns of maximum temperature at some major use and urbanization. )e two holly cities Makkah and ° ° ° cities such as Makkah (21.43 N, 39.79 E), Madinah (24.54 N, Madinah are well developed from the historical period where ° ° ° 39.70 E), and Riyadh (24.92 N, 46.72 E), as well as the average the model underestimated maximum temperature. )is is in over 27 stations across Saudi Arabia, obtained from RegCM4- line with the general cold bias by the RegCM4 [17]. On the simulated averages from HadGEM2 and ECHAM6, along other hand, the capital city Riyadh is expanding with new with ERA-Int-driven runs and surface observations, are shown infrastructures and development programs and rapid growth of in Figure 12. In general, the simulated maximum temperature urbanization where RegCM4 overestimates maximum tem- perature. )is is similar to the warm bias over Oman/Yemen as follows the pattern of observations closely. For Makkah and Madinah, the ERA-Int is very close to the observations reported in [17] and by Wang and Xubin (2013) which might (Figures 12(a) and 12(b)), while for Riyadh (Figure 12(c)), it is be due to some error or low dense network data coverage in the overestimated by around 3.5 C (Figure 12(d)). )e average observations. )erefore, this temperature underestimation by temperature of Makkah over the common period of 1985– the climate model at some locations and overestimation at ° ° 2014 is 38.26 C (38.55 C) from observations (ERA-Int) while it other locations are an unresolved issue and need further in- is 35.86 C from the RegCM4 simulation. For Madinah, the vestigation. Hence, model simulations can provide the overall average temperature over the common period of 1985–2014 is pattern of the observed maximum temperature at local scale. ° ° 35.21 C (35.66 C) from observations (ERA-Int) while it is However, bias varies from location to location and needs to be Frequency (days) Frequency (days) 1961 1961 1966 1966 1971 1971 1976 1976 1981 1981 1986 1986 1991 1991 1996 1996 2001 2001 2006 2006 2011 2011 2016 2016 2021 2021 2026 2026 2031 2031 2036 2036 2041 2041 2046 2046 2051 2051 2056 2056 2061 2061 2066 2066 2071 2071 2076 2076 2081 2081 2086 2086 2091 2091 2096 2096 Frequency (days) Frequency (days) 1961 1961 1966 1966 1971 1971 1976 1976 1981 1981 1986 1986 1991 1991 1996 1996 2001 2001 2006 2006 2011 2011 2016 2016 2021 2021 2026 2026 2031 2031 2036 2036 2041 2041 2046 2046 2051 2051 2056 2056 2061 2061 2066 2066 2071 2071 2076 2076 2081 2081 2086 2086 2091 2091 2096 2096 Advances in Meteorology 13 45°N 45°N 130 130 40°N 40°N 120 120 110 110 35°N 35°N 100 100 30°N 30°N 90 90 25°N 25°N 80 80 70 70 20°N 20°N 55 55 15°N 15°N 45 45 10°N 10°N 35 35 5°N 5°N 15 15 EQ EQ 5 5 5°S –1 5°S –1 (a) (b) 45°N 45°N 130 130 40°N 40°N 110 110 35°N 35°N 100 100 30°N 30°N 90 90 25°N 25°N 80 80 70 70 20°N 20°N 55 55 15°N 15°N 45 45 10°N 10°N 35 35 25 25 5°N 5°N 15 15 EQ EQ 5 5 5°S 5°S –1 –1 (c) (d) 45°N 45°N 40°N 40°N 9 9 3 3 35°N 35°N –3 –3 30°N 30°N –9 –9 25°N 25°N –15 –15 –21 –21 20°N 20°N –27 –27 15°N 15°N –33 –33 10°N –39 10°N –39 –45 –45 5°N 5°N –51 –51 EQ EQ –57 –57 5°S 5°S –65 –65 (e) (f) 45°N 45°N 15 15 40°N 40°N 9 9 3 3 35°N 35°N –3 –3 30°N 30°N –9 –9 25°N –15 25°N –15 –21 –21 20°N 20°N –27 –27 15°N 15°N –33 –33 10°N 10°N –39 –39 –45 –45 5°N 5°N –51 –51 EQ EQ –57 –57 5°S –65 5°S –65 (g) (h) Figure 10: Spatial distribution of changes in hot days (T > 50 C) for (a) RCP4.5 near future, (b) RCP4.5 far future, (c) RCP8.5 near future, max and (d) RCP8.5 far future along with cold nights (T < 5 C) for (e) RCP4.5 near future, (f) RCP4.5 far future, (g) RCP8.5 near future, and min (h) RCP8.5 far future with respect to the base period (1971–2000). Average is taken over HadGEM2- and ECHAM6-driven runs. 21°W 21°W 21°W 21°W 14°W 14°W 14°W 14°W 7°W 7°W 7°W 7°W 0 0 0 0 7°E 7°E 7°E 7°E 14°E 14°E 14°E 14°E 21°E 21°E 21°E 21°E 28°E 28°E 28°E 28°E 35°E 35°E 35°E 35°E 42°E 42°E 42°E 42°E 49°E 49°E 49°E 49°E 56°E 56°E 56°E 56°E 63°E 63°E 63°E 63°E 70°E 70°E 70°E 70°E 21°W 21°W 21°W 21°W 14°W 14°W 14°W 14°W 7°W 7°W 7°W 7°W 0 0 0 0 7°E 7°E 7°E 7°E 14°E 14°E 14°E 14°E 21°E 21°E 21°E 21°E 28°E 28°E 28°E 28°E 35°E 35°E 35°E 35°E 42°E 42°E 42°E 42°E 49°E 49°E 49°E 49°E 56°E 56°E 56°E 56°E 63°E 63°E 63°E 63°E 70°E 70°E 70°E 70°E 14 Advances in Meteorology T ≥ 50°C max 2021– 2031– 2041– 2051– 2061– 2071– 2081– 2091– 2030 2040 2050 2060 2070 2080 2090 2100 CORDEX Arabian Peninsula (a) T ≤ 5°C min 2021– 2031– 2041– 2051– 2061– 2071– 2081– 2091– 2030 2040 2050 2060 2070 2080 2090 2100 CORDEX Arabian Peninsula (b) ° ° Figure 11: Decadal variations of the number of hot days (T ≥ 50 C) and cold nights (T ≤ 5 C) with respect to the reference period max min (1971–2000) obtained from average of HadGEM2- and ECHAM6-driven runs under RCP8.5 for (a) CORDEX-MENA/Arab domain and (b) Arabian Peninsula subdomain. st considered when using the model data in application-oriented end of the 21 century. Based on Figure 12, the maximum tasks such as heat index calculations. )e model-simulated temperature simulations based on the RCP8.5 (RCP4.5) relative humidity for each panel indicates an insignificant rate scenarios show the following features at some major cities in of decrease. )is indicates that because the temperature will Saudi Arabia: increase in the future, warmer air’s larger capacity to store (i) At Makkah, the maximum temperature increase water vapor may cause decrease of relative humidity. rate is projected to be 0.51 (0.30), 0.60 (0.28), and For all station averages, the simulations reveal similar 0.76 (0.06) C per decade for the periods 1961–2100, patterns for both the RCP8.5 and RCP4.5 scenarios until the 2021–2050, and 2071–2100, respectively mid-2030s. After that, the RCP8.5-based projections deviate to higher values compared to those of RCP4.5. )e difference (ii) At Madinah, the maximum temperature increase between projected values for the two RCPs is about 3 C at the rate is projected to be 0.54 (0.34), 0.57 (0.34), and Changes in frequency (days/decade) Changes in frequency (days/decade) –118 15 –278 184 –137 28 –310 244 –179 56 –420 360 –200 108 –419 367 –226 216 –514 497 –272 324 –605 –290 442 –651 622 –310 568 –675 706 Advances in Meteorology 15 42 70 42 70 40 60 40 60 38 50 38 50 36 40 36 40 34 30 34 30 32 20 32 20 30 10 30 10 28 0 28 0 RCP8.5 RCP4.5 RCP8.5 RCP4.5 Had and ECHAM Had and ECHAM Had and ECHAM Had and ECHAM ERA–Int Obs ERA–Int Obs RH4.5 RH8.5 RH4.5 RH8.5 (a) (b) 42 70 42 70 40 60 40 60 38 50 38 50 36 40 36 40 34 30 34 30 32 20 32 20 30 10 30 10 28 0 28 0 RCP8.5 RCP4.5 RCP8.5 RCP4.5 Had and ECHAM Had and ECHAM Had and ECHAM Had and ECHAM ERA–Int Obs ERA–Int Obs RH4.5 RH8.5 RH4.5 RH8.5 (c) (d) Figure 12: Simulated maximum temperature extracted nearer grid point of the station locations for (a) Makkah, (b) Madinah, (c) Riyadh, and (d) Saudi Arabia (averaged over 27 stations) for both RCP4.5 and RCP8.5 along with ERA-Int and surface observational data. For RegCM simulations, average taken from HadGEM2- and ECHAM6-driven runs are also shown by solid lines. Shaded area shows the range. )e relative humidity (in %) is also shown for each panel (RH85 and RH45 for, respectively, RCP8.5 and RCP4.5). 0.66 (0.03) C per decade for the periods 1961–2100, 4. Conclusions 2021–2050, and 2071–2100, respectively st In this study, the change in temperature in the 21 century (iii) At Riyadh, the maximum temperature increase rate over the CORDEX-MENA domain with a focus on the is projected to be 0.59 (0.38), 0.70 (0.27), and 0.69 Arabian Peninsula has been projected from RegCM4 sim- (0.15) C per decade for the periods 1961–2100, ulations. Data from the three CMIP5 models HadGEM2, 2021–2050, and 2071–2100, respectively ECHAM6, and CanESM were downscaled with RegCM4 (iv) Over Saudi Arabia, the maximum temperature (RegCM4-HadGEM2, RegCM4-ECHAM6, and RegCM4- increase rate is projected to be 0.59 (0.41), 0.63 CanESM). )e RegCM4-CanESM variant largely over- (0.29), and 0.67 (0.10) C per decade for the pe- estimated the mean temperature in the past climate and was riods 1961–2100, 2021–2050, and 2071–2100, found to be not useful in climate projection over the analysis respectively domain. )e maximum temperatures extracted at few main )e increase rates for the above three stations, and cities in Saudi Arabia were also projected. )e analysis included two RCPs scenarios, namely, RCP4.5 and RCP8.5. averaged over all stations, are significant at the 95% level. Overall, the simulated maximum temperature follows the In general, the RegCM4 simulations with RCP8.5 were likely to project a warmer climate than those conducted with pattern of observations. However, caution is recommended before the use of model temperature for application- RCP4.5. )e RCP8.5 scenario projected a temperature in- oriented tasks which vary from location to location. crease of about 7 C over the Arabian Peninsula by the end of st )erefore, the uncertainty at each location must be con- the 21 century. )is increase in temperature is more sidered for climate change impact studies using model data. pronounced during the winter season than during the Further study may require using data from the newly summer. Over the entire domain, the temperature is pro- developed Saudi-KAU Global Climate Model and focusing jected to increase at the rate of 0.73 (0.27), 0.59 (0.39), and 0.79 (0.20) C per decade under RCP8.5 (RCP4.5) scenarios, on the simulation of climate over the Arabian Peninsula [52–54]. for the periods 2021–2100, 2021–2050, and 2071–2100, T (°C) T (°C) max max 1965 1965 1973 1973 1981 1981 1985 1985 1989 1989 1993 1993 1997 1997 2001 2001 2005 2005 2009 2009 2013 2013 2017 2017 2021 2021 2025 2025 2029 2029 2033 2033 2037 2037 2041 2041 2045 2045 2049 2049 2053 2053 2057 2057 2061 2061 2065 2065 2069 2069 2073 2073 2077 2077 2081 2081 2085 2085 2089 2089 2097 2097 RH (%) RH (%) T (°C) T (°C) max max 1961 1961 1965 1965 1969 1969 1973 1973 1977 1977 1981 1981 1985 1985 1989 1989 1993 1993 1997 1997 2005 2005 2009 2009 2013 2013 2017 2017 2021 2021 2025 2025 2029 2029 2033 2033 2037 2037 2041 2041 2045 2045 2049 2049 2053 2053 2057 2057 2061 2061 2065 2065 2069 2069 2073 2073 2077 2077 2081 2081 2085 2085 2089 2089 2093 2093 2097 2097 RH (%) RH (%) 16 Advances in Meteorology respectively. )e rate of increase in temperature over the Supplementary Materials Arabian Peninsula subdomain is projected to be 0.72 (0.29), Sup 1: distribution of air temperature (in C) obtained from 0.60 (0.30), and 0.83 (0.25) C per decade under the RCP8.5 (a) annual CRU, (b) annual ERA-Int, (c) winter CRU, (d) (RCP4.5) scenario, for the periods 2021–2100, 2021–2050, winter ERA-Int, (e) summer CRU, and (f) summer ERA-Int and 2071–2100, respectively. )e RCP8.5-projected hot ° averaged for the common period 1980–2005. )e 11 sub- days (T ≥ 50 C) are likely to increase at the rate of 8.01 max domains are drawn following Almazroui (2016) and aver- (11.40) days per decade, while the decrease in cold nights aged over these subdomains represent the CORDEX- (T ≤ 5 C) is projected to be −2.95 (−6.14) nights per min MENA/Arab domain used for objective analysis later on. decade for the CORDEX (Arabian Peninsula) domain. All Sup 2: spatial distribution of changes in RegCM4-simulated increasing trends in temperature and in hot day numbers mean temperature under RCP4.5 for (a) annual near future, and decreasing trends in cold nights are statistically sig- (b) annual far future (top right), (c) winter season near nificant at the 95% level. )ese provide a clear indication of future, (d) winter season far future, (e) summer season near a warming climate in the future over the Arabian Penin- future, and (f) summer season far future. Data are averaged sula, even if the warming may vary from region to region. from HadGEM2- and ECHAM6-driven runs. )e change is )e projected warming rate over the Arabian Peninsula is calculated as average of near (or far far) future minus the larger than that over the entire domain. )e RegCM4-based base period value. Sup 3: changes in RegCM4 mean tem- temperature follows the pattern of surface observations at perature ( C) in the future climate under RCP8.5 with re- the station level across Saudi Arabia. )erefore, spect to the base period (1971–2000) for (a) annual near HadGEM2- and ECHAM6-driven runs are recommended future, (b) annual far future, (c) winter season near future, as input databases for environmental vulnerability as- (d) winter season far future, (e) summer season near future, sessment studies since the CanESM output was found to be and (f) summer season far future. Data are averaged from unsuitable. However, more CMIP5 models may be eval- HadGEM2- and ECHAM6-driven runs. (Supplementary uated for their utility in application-oriented tasks in Materials) further studies. Data Availability References )e data are run in the supercomputer of the King [1] Y. K. 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Temperature Changes over the CORDEX-MENA Domain in the 21st Century Using CMIP5 Data Downscaled with RegCM4: A Focus on the Arabian Peninsula

Advances in Meteorology , Volume 2019 – May 20, 2019

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Hindawi Publishing Corporation
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The data are run in the supercomputer of the King Abdulaziz University, Jeddah, Saudi Arabia, and it is difficult to share as the data are in gigabyte and there is no way to share the data to the public. We can share the results through the publishing of this paper, and the results can be compared with other studies that have been done over the region. However, some of the data are freely accessible such as (1) GCMs data that are used in the simulations and (2) CRU and CMIP5 data that are available for free and are known to the scientific community GAMEP data for the surface local observations are not for distribution. These data cannot be shared as copyright of the data used is applied for using these data, and if anyone would like to use has to obtain those from the source. Copyright © 2019 Mansour Almazroui. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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1687-9309
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1687-9317
DOI
10.1155/2019/5395676
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Abstract

Hindawi Advances in Meteorology Volume 2019, Article ID 5395676, 18 pages https://doi.org/10.1155/2019/5395676 Research Article Temperature Changes over the CORDEX-MENA Domain in the st 21 Century Using CMIP5 Data Downscaled with RegCM4: A Focus on the Arabian Peninsula Mansour Almazroui Center of Excellence for Climate Change Research/Department of Meteorology, King Abdulaziz University, Jeddah 21589, Saudi Arabia Correspondence should be addressed to Mansour Almazroui; mansour@kau.edu.sa Received 25 December 2018; Revised 21 March 2019; Accepted 22 April 2019; Published 20 May 2019 Academic Editor: Jorge E. Gonzalez Copyright © 2019 Mansour Almazroui. )is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. )is paper examined the temperature changes from the COordinated Regional climate Downscaling Experiment (CORDEX) over st the Middle East and North Africa (MENA) domain called CORDEX-MENA. )e focus is on the Arabian Peninsula in the 21 century, using data from three Coupled Model Intercomparison Project Phase 5 (CMIP5) models downscaled by RegCM4, a regional climate model. )e analysis includes surface observations along with RegCM4 simulations and changes in threshold st based on extreme temperature at the end of the 21 century relative to the base period (1971–2000). Irrespective of the driving CMIP5 models, the RegCM4 simulations show enhanced future temperature changes for RCP8.5 as compared to RCP4.5. )e ° ° Arabian Peninsula will warm at a faster rate (0.83 C per decade) as compared to the entire domain (0.79 C per decade) for RCP8.5 ° ° during the period 2071–2100. Moreover, the number of hot days (T ≥ 50 C) (cold nights: T ≤ 5 C) will increase (decrease) max min faster in the Arabian Peninsula as compared to the entire domain. )is increase (decrease) of hot days (cold nights) will be more prominent in the far future (2071–2100) as compared to the near future (2021–2050) period. Moreover, the future changes in temperature over the main cities in Saudi Arabia are also projected. )e RegCM4-based temperature simulation data from two suitable CMIP5 models are recommended as a useful database for further climate-change-related studies. frequent heavy rainfall events occurred in Saudi Arabia over 1. Introduction the last decade and temperature often exceeded 50 C, and In the present era of climate change, a proper assessment of even reached 52 C in 2010 [2, 3]. Such events need to be vulnerable sectors is important in developing strategies for predicted because heavy rainfall events cause flash floods the adaptation and long-term planning by national policy- and high temperatures can cause heat strokes. Local people, makers and other stakeholders. In this regard, an accurate migrant populations, and the Pilgrims from all over the climate database is one of the main prerequisites for climate world, are all very vulnerable when exposed to these phe- change impacts studies, which remain scarce in the Arab nomena. In this connection, reliable climate projections, region, particularly in the Arabian Peninsula. )e climate of including increased utilization of climate model data, are the Arab region is generally governed by the synoptic-scale essential for the region. forcing (e.g., sea surface temperature, moisture, and wind) For the years 1956–2005, the Intergovernmental Panel coming from the Indian and Atlantic oceans, while the on Climate Change (IPCC) has reported a global warming Indian Ocean, the Mediterranean Sea, and Sudan low (low trend of 0.13 C/decade [4], and in the updated fifth as- pressure zone over East Africa) control the Arabian Pen- sessment report (AR5), it was updated to 0.12 C/decade for insula’s climate [1]. )e regional climate projection for the the period 1951–2012 [5]. )is global warming and Arabian Peninsula is a challenging task. For example, associated climate change undoubtedly has long-term 2 Advances in Meteorology no topographic information at finer scales. To overcome this consequences for many socioeconomic sectors, such as water consumption, power generation, human health, bio- problem, RCMs are considered to be the best tools for downscaling GCM-generated climatic features, to obtain diversity, and ecosystems. )ese may be contributory factors to the formation of certain atmospheric pollutants associ- more detailed climate information over a particular region ated with the rise in air temperature [6–8]. )e rise of air [23, 24]. RCMs are also invaluable over areas where ob- temperature is likely to lead to an increase in air pollutants servations are either scarce or absent, as over the Arab [9]. )e IPCC also projected a possible increase in frequency region. )e RCMs outperform the driving global climate and intensity of extreme temperatures over the Arabian models and provide added value to simulate the climate of a Peninsula [4]. In the coming decades, climate change could region [25]. )us, dynamic downscaling of GCM simula- have a significant impact on water supplies in many parts of tions has been a widely used and acceptable strategy [26, 27]. the globe and particularly in the semiarid/arid regions. In other words, an RCM can be used to generate future climate simulations as well as to help understand the past )erefore, these impacts might be more severe for the Arabian Peninsula, and in particular, for Saudi Arabia, climate in a particular region. )us, the climate variables generated by a suitable RCM can be used in extreme analysis which contains the world’s largest continuous sand desert, the Rub Al-Khali [2, 3, 10]. in the Arab region, focusing on the Arabian Peninsula In the temperature climatology of Saudi Arabia, the (particularly Saudi Arabia), for the projection period. northern side is colder than the southern side [11]. In the )erefore, this paper aimed to investigate the changes in ° ° ° extreme north, the temperature ranges from 8.57 C to temperature over the CORDEX-MENA domain (27 W–76 E ° ° ° 28.32 C through the different seasons, while it ranges from and 7 S–45 N) with a focus on the Arabian Peninsula during st ° ° 26.68 C to 33.97 C in the southern regions. )e ocean does the 21 century, by using data from three GCMs from not contribute to the rapid increase of temperature in the CMIP5 project downscaled with an RCM, namely, regional Arabian Peninsula as the ocean temperature increases more climate model system updated in 2010 (RegCM4). slowly than land temperature in the peninsula [12]. Changes )e CORDEX-MENA domain is defined using sensi- in the climate, and particularly changes in temperature, tivity tests from seven related domains. Details of the do- increase the risk of extreme events such as heat and cold main selection along with the reason for selecting this new waves, in addition to more frequent droughts and probable domain within the CORDEX framework are provided in drought intensification [13]. )e trends of annual and [28]. )e analysis is mainly focused over Saudi Arabia (about seasonal extreme indices over Saudi Arabia over recent 80% area of the Arabian Peninsula) which is a region with decades were studied by [14], who reported a warming trend scarce climate change studies. In order to understand the over the region. Moreover, climate change is likely to be the possible changes in temperature, the corrected temperature most dangerous threat to regional biodiversity [15]. is projected into the future. )is paper also aims to in- Moreover, the Arab region, and particularly the Arabian vestigate extreme temperatures using thresholds for warm Peninsula, is one of the most vulnerable areas to the po- and cold days from regional to local scales and validate with tential threats listed under the dry-land ecosystems [16]. ground stations across Saudi Arabia. Model-generated climatic information for both near and more distant future periods is required to assist with long- 2. Data and Methodology term planning. In this connection, a global climate model (GCM) is the only tool that can generate future climate [17]. 2.1. Model Description. )e regional climate model )e IPCC AR5 report used the Coupled Model In- (RegCM) is a limited-area model developed by the Abdus tercomparison Project Phase 5 (CMIP5) multimodel data- Salam International Centre for )eoretical Physics (ICTP), base developed under the World Climate Research Program. Trieste, Italy, for the purpose of long-term climate simu- Downscaling is usually used to transform the GCM outputs lation. )is model is used by a large community of re- into a more suitable form [18]. Dynamical downscaling is searchers to study regional climate, including over the based on physical models which are in fact the regional CORDEX-MENA domain (e.g., [17, 29]). Details about climate models (RCMs). Statistical downscaling is another RegCM version 4.3.4 (RegCM4) are available in [30]. procedure based on empirical nature where downscaled RegCM4 uses the dynamical core from [31] and the radi- projections remain constant over time [19]. It is used to ation scheme from [32, 33]. )e BATS (biosphere and at- project the climatic variables used by many researchers mosphere transfer scheme) from [34, 35] and the CLM (e.g., [18, 20, 21]). )ere are advantages and disadvantages in (community land model) from [36] are also used. )e PBL both dynamical and statistical downscaling procedures. )e (planetary boundary layer) and ocean fluxes are from statistical downscaling is cheaper and consumes less com- [37, 38], respectively. puting resources [18]. Because our aim is to understand the Multiple cumulus convection schemes are available climate variability, the use of dynamical downscaling is within RegCM4. Among them, the schemes in [39, 40] and preferred for this analysis where physical parameterization Arakawa–Schubert schemes are assimilated into the more can be selected for optimized results. )e CMIP5 GCMs are general Grell convection parameterization scheme. )e generally coarse resolution (100–300 km) models and are not combination of Grell and Emanuel [28], or either of them suitable for generating detailed climatic conditions over a uniquely, can be used for land and ocean masking. In the specific region [22]. GCMs cannot simulate the detailed present study, the European Centre for Medium-Range structure of regional climatic phenomena because they have Weather Forecasts (ECMWF) Reanalysis (ERA-Interim, Advances in Meteorology 3 ° ° hereafter refereed as ERA-Int) 0.75 × 0.75 gridded 6-hourly simulated temperature data were extracted for 11 sub- data (http://www.ecmwf.int/products/data/archive) are used domains within the entire domain (Figure 1), as well as for to provide initial conditions for three CMIP5 model sim- the 27 meteorological station locations across Saudi Arabia. ulations of both past and future climate. RegCM4 is forced )e ground-truth station data were collected from the by ERSST, the extended reconstructed sea surface temper- General Authority of Meteorology and Environmental ature data. )e Coordinated Regional climate Downscaling Protection (GAMEP). )e data extraction near the grid Experiment (CORDEX) recommended use of RegCM4 at point of each meteorological station was done as in [45, 46]. 50 km resolution, as used in this study, though it may also be In this procedure, the station data are interpolated from the used at higher resolutions [28]. nearest points of a grid to where the station is located. Details of how the 11 subdomains adopted in this study were selected are available in [28, 29], and the characteristics 2.2. Experimental Setup. )ree CMIP5 models, namely, the of the 27 meteorological stations may be found in [2, 3]. )e HadGEM2 (the UK Met Office Hadley Centre Global En- extracted data are processed on daily, monthly, and annual ° ° vironment Model version 2, 1.2 ×1.8 [41]); CanESM (the time scales and objectively compared with the observed/ Canadian Earth System Model of the Canadian Centre for gridded datasets over the same temporal scale. Regression ° ° Climate Modeling and Analysis (CCCma), 2.8 × 2.8 [42]; coefficients are obtained for temperature (mean, maximum, and ECHAM6 (Atmospheric GCM of Max Planck Institute and minimum) of both observed and RegCM4 datasets. )e ° ° for Meteorology, Germany, 1.8 ×1.8 [43]), are used for the relative temperature is calculated as each time series minus past climate study. In addition, two representative con- the 1971–2000 average of each source. As in [28], the better centration pathways (RCPs), i.e., RCP4.5 and RCP8.5 are land-surface option within RegCM4 is selected for each used for the future climate projections. )e use of subdomain and for the entire domain. For this purpose, HadGEM2, CanESM, and ECHAM6 is based on [28]. An statistical measures such as mean, bias, correlation (r), root additional simulation of past climate has also been carried mean square difference (RMSD), and standard deviation out using ERA-Int reanalysis as the input in RegCM4. As (Std) against CRU values are used. mentioned above, the RCM domain extending from 7 S to Daily data are used to analyze extreme temperatures ° ° ° 45 N and 27 W to 76 E encompasses the Arab region and is such as hot days and cold nights with a certain threshold adopted from [28]. )is domain is sufficiently large for RCM temperature. In this analysis, hot days and cold nights are simulations and is known as the CORDEX-MENA domain defined as those with maximum temperature greater than or (see [28]). )is domain was obtained from seven sensitivity ° ° equal to 50 C (T ≥ 50 C) and minimum temperature less max experiments, and it fits well with the CORDEX Arab do- ° ° than or equal to 5 C (T ≤ 5 C), respectively. )e change in min main. Results of the sensitivity experiments (not shown hot days and cold nights was calculated as the number of here) indicate a better performance of the land surface days/nights in a projected year minus the average number of scheme BATS (not CLM) for the analysis domain [28]. )is days/nights over the base period. As given in [12], simple study follows the recommendation in [29] to use the Grell regression methods were employed for trend analysis, while convection scheme over land and the Emanuel scheme over trend significance was assessed using the F-test. )e pro- the ocean within the analysis domain. jected temperature was obtained from six simulations (listed Prior to starting the long run of the historical and future in Table 1) for the entire domain and each subdomain, for climates, a number of sensitivity experiments (spanning both near and far future periods, using RCP4.5 and RCP8.5 2000–2005) were completed with different convective pa- scenarios. Finally, the future changes in temperature were rameterization schemes, domains, and land surface schemes computed for both the near and far future periods with in order to select the best domain, the most suitable con- respect to the past climate. )e corrected temperature was vection scheme, and the best land surface scheme (see obtained by adding the base period (1971–2000) bias to the [17, 28, 29]). Later on, a total of 10 simulations were per- projected temperature, and the future climate anomaly was formed using the optimal settings of RegCM4.6 model, as obtained by subtracting the average from each time series. listed in Table 1. All simulations for this study using RegCM4.6 were performed at 50 km resolution in a single 3. Results and Discussion domain without further nesting. 3.1. Past Climate Temperature. )e mean air temperature 2.3. Analysis Procedures. )e interannual variability of (at 2 m) averaged over all subdomains (i.e., CORDEX) in- simulated air temperature (2 m) for the entire domain and a dicates that model-simulated values correspond well with the subdomain over the Arabian Peninsula was compared with observations over the annual cycle (Figure 2(a)). However, observations of the past climate (1971–2000) from the there is a little underestimation by RegCM4-HadGEM2 Climatic Research Unit (CRU) dataset [44]. Simulated (−1.17 to −2.62 C w.r.t. CRU) and RegCM4-ECHAM6 temperature biases (model minus observation) were also (−0.91 to −1.91 C w.r.t. CRU) as compared to the CRU calculated with the CRU data. )e CRU gridded dataset has a and ERA-Int data, while there is very large overestimation by ° ° ° spatial resolution of 0.5 , the same as the RegCM4 runs. RegCM4-CanESM (6.95 C to 11.63 C w.r.t. CRU). Similar Changes in temperature were generated for two future behavior in the mean temperature is also present in the in- periods, the near future (2021–2050) and the far future dividual subdomains, such as the subdomain over the Arabian (2071–2100), relative to the base period. )e RegCM4- Peninsula (Figure 2(b)). In this subdomain, ERA-Int also 4 Advances in Meteorology Table 1: List of simulations performed in this study. No. Simulation name Simulation period Boundary conditions RCPs 1 RegCM4-ERA-Int 1979–2015 ERA-Interim – 2 RegCM4-HadGEM2 1960–2005 HadGEM2 hist 3 RegCM4-CanESM 1960–2005 CanESM hist 4 RegCM4-ECHAM6 1960–2005 ECHAM6 hist 5 RegCM4-HadGEM2 2006–2100 HadGEM2 RCP4.5 6 RegCM4-CanESM 2006–2100 CanESM RCP4.5 7 RegCM4-ECHAM6 2006–2100 ECHAM6 RCP4.5 8 RegCM4-HadGEM2 2006–2100 HadGEM2 RCP8.5 9 RegCM4-CanESM 2006–2100 CanESM RCP8.5 10 RegCM4-ECHAM6 2006–2100 ECHAM6 RCP8.5 45°N averages from RegCM4-HadGEM2 and RegCM4-ECHAM6 40 °N 3500 were used in the rest of the analysis. 35 °N 3000 Spatial distributions of mean temperature obtained from 30 °N CRU and RegCM4-ERA-Int show similar patterns of an- 25 °N 2000 nual, winter, and summer temperatures (Sup 1). At annual 20 °N scale, the temperature in the latitudinal band from 5–25 N is 15 °N ° 1000 slightly too high and is relatively higher to the south of 15 N 10 °N 500 during the winter season. )e highest temperature is ob- 5°N 100 served in the band from 15–35 N in the summer season. EQ 10 Spatial distributions of simulated temperature bias for 5°S the two CMIP5 models downscaled using RegCM4 show that the RegCM4-HadGEM2 and RegCM4-ECHAM6 underestimate temperature relative to CRU observations Figure 1: Analysis domain with 11 subdomains. )e subdomain A at both annual and seasonal scales (Figure 3). Quantifying is over the Arabian Peninsula which is focused in this analysis for the temperature bias (model minus observation), the un- detail study. )e elevation (in meters) indicates the topography of derestimation by RegCM4-HadGEM2 and RegCM4- the domain. ° ° ECHAM6 is about 2 C to 3 C for most of the domain at annual scale (Figures 3(a) and 3(b)). )ere is a dipole underestimates (−0.51 to −2.54 C) mean temperature com- anomaly in the RegCM4-simulated temperature distribu- pared to the CRU data. Note that CRU is the observed data tion over the Arabian Peninsula: the overestimation (un- gridded over the region while ERA-Int is the reanalysis data derestimation) or positive (negative) bias over southeast generated using the assimilation system. In the case of (northwest) Arabian Peninsula for RegCM4-HadGEM2 RegCM4-ECHAM6, the underestimation (−0.92 to −1.14 C) and RegCM4-ECHAM6. )is dipole anomaly in the dis- occurs mostly during the winter months, while for RegCM4- tribution of temperature in two different areas is most HadGEM2, the underestimation occurs all year round. For obvious in the summer season (JJA; Figures 3(e) and 3(f)) RegCM4-CanESM, the large overestimation is for all months as compared to the winter season (DJF) (Figures 3(c) and 3(d)). during the year. During the summer months, the over- ° ° estimation by RegCM4-CanESM can reach above 10 C In the summer months, warm bias exceeds 7 C over ° ° (11.04 C to 11.90 C). )e temperature annual cycle for both Yemen/Oman for the RegCM4 simulations, while studies the CORDEX domain and the Arabian Peninsula subdomain [17, 29] report that it exceeds 8 C for the dry season months shows underestimation (e.g., RegCM4-HadGEM2 and (JJAS). A similar large bias in the ERA-40 and ECHAM5 RegCM4-ECHAM6) by some models and overestimation driving fields, compared to RegCM3 simulations of annual (e.g. RegCM4-CanESM) by the other, relative to the tem- temperature over this region, particularly over the south- perature climatology. )e temporal evolution of the relative western Arabian Peninsula, has also been reported by [25]. temperature (i.e., each time series minus the 1971–2000 av- )ey concluded that RegCM usually simulates lower tem- erage of each source) for the entire domain and Arabian peratures than the forcing data; i.e., RegCM3 reduced the Peninsula subdomain (Figures 2(c) and 2(d)) indicates that warm bias that was seen in the HadGEM2- and ECHAM6- there is an increase in temperature over time for all time driven runs. series. )e 10-year moving average indicates a clear trend in Over the entire domain, RegCM4-CanESM simulates the relative temporal evolution. In this analysis, RegCM4- higher temperatures than observed by CRU and ERA-Int, CanESM overestimated the temperature more than 10 C; an while RegCM4-HadGEM2 and RegCM4-ECHAM6 simu- overestimation of about 8 C was also reported by [28]. Be- late slight lower temperatures (Figure 4). For the entire cause we use the same RegCM4 to downscale the CMIP5 domain, RegCM4-HadGEM2 (RegCM4-ECHAM6) un- ° ° models, the large overestimation in RegCM4-CanESM may derestimates temperature by 1.93 C (1.36 C) (Figure 4(a)). be transformed from the global climate model. )erefore, A similar situation is also noticed for the Arabian Pen- RegCM4-CanESM was not considered further, and only insula subdomain. In this subdomain, the temperature 21 °W 14 °W 7°W 7°E 14 °E 21 °E 28 °E 35 °E 42 °E 49 °E 56 °E 63 °E 70 °E Advances in Meteorology 5 45 45 40 40 35 35 30 30 25 25 20 20 15 15 10 10 5 5 0 0 CRU ERA-Int CRU ERA-Int RegCM4-HadGEM RegCM4-ECHAM RegCM4-ECHAM RegCM4-HadGEM RegCM4-CanESM RegCM4-CanESM (a) (b) 2.10 2.10 1.60 1.60 1.10 1.10 0.60 0.60 0.10 0.10 –0.40 –0.40 –0.90 –0.90 –1.40 –1.40 10-year moving average CRU 10-year moving average CRU (CRU) (CRU) ERA–Int 10-year moving average ERA–Int 10-year moving average (RegCM4–HadGEM) (RegCM4–HadGEM) RegCM4–HadGEM 10-year moving average RegCM4–HadGEM 10-year moving average (RegCM4–ECHAM) (RegCM4–ECHAM) RegCM4–ECHAM 10-year moving average RegCM4–ECHAM 10-year moving average (RegCM4–CanESM) (RegCM4–CanESM) RegCM4–CanESM RegCM4–CanESM (c) (d) Figure 2: Annual cycle average temperature for (a) CORDEX-MENA/Arab domain and (b) Arabian Peninsula subdomain for the present climate 1971–2005. Temporal evolution for the relative temperature (each time series minus the 1971–2000 average of each source) for (c) CORDEX-MENA/Arab domain and (d) Arabian Peninsula subdomain. ° ° underestimations are 1.83 C and 4.43 C, by RegCM4- compared for two scenarios and three CMIP5 models HadGEM2 and RegCM4-ECHAM6, respectively, with (Figure 5). )e mean temperature for each CMIP5 model reference to the CRU data (Figure 4(b)). )e bias may come and two RCPs for the near and far future averaged over 11 from the RegCM4 itself for its parameterization or may be subdomains of the entire domain, and the Arabian from the inherent to the CMIP5 modeling systems. Peninsula subdomain, indicates that both RegCM4- HadGEM2 and RegCM4-ECHAM6 simulate nearly sim- ilar temperature (Figure 5). For RCP8.5, the average from 3.2. Projected Changes in Temperature. Before analyzing the RegCM4-HadGEM2 and RegCM4-ECHAM6 is 25.03 C ° ° ° changes in future temperature, the RegCM4-simulated (23.66 C) for the near future and 28.69 C (27.27 C) for the temperatures for the near and far future periods are far future, over the entire domain (Arabian Peninsula Temperature anomaly (°C) Temperature (°C) JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV 2003 DEC Temperature anomaly (°C) Temperature (°C) JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 2003 6 Advances in Meteorology 45°N 45°N 40°N 40°N 35°N 35°N 30°N 30°N 25°N 25°N 20°N 20°N 15°N 15°N 10°N 10°N 5°N 5°N EQ EQ 5°S 5°S C C –7 –6 –5 –4 –3 –2 –1 –0.5 0.5 1234567 –7 –6 –5 –4 –3 –2 –1 –0.5 0.5 1234567 (a) (b) 45°N 45°N 40°N 40°N 35°N 35°N 30°N 30°N 25°N 25°N 20°N 20°N 15°N 15°N 10°N 10°N 5°N 5°N EQ EQ 5°S 5°S C C –7 –6 –5 –4 –3 –2 –1 –0.5 0.5 1234567 –7 –6 –5 –4 –3 –2 –1 –0.5 0.5 1234567 (c) (d) 45°N 45°N 40°N 40°N 35°N 35°N 30°N 30°N 25°N 25°N 20°N 20°N 15°N 15°N 10°N 10°N 5°N 5°N EQ EQ 5°S 5°S C C –7 –6 –5 –4 –3 –2 –1 –0.5 0.5 1234567 –7 –6 –5 –4 –3 –2 –1 –0.5 0.5 1234567 (e) (f) Figure 3: Spatial distribution of air temperature bias (in C) with respect to CRU data for (a) annual RegCM4-HadGEM2, (b) annual RegCM4-ECHAM6, (c) winter RegCM4-HadGEM2, (d) winter RegCM4-ECHAM6, (e) summer RegCM4-HadGEM2, and (f) summer RegCM4-ECHAM6 averaged over the common period 1971–2000. subdomain). In this case, the standard deviation is 0.55 0.38 (0.38) for the near future and 0.36 (0.46) for the far (0.58) for the near future and 0.77 (0.90) for the far future future over the entire domain (Arabian Peninsula sub- over the entire domain (Arabian Peninsula subdomain). domain). )is clearly indicates that the RCP8.5 simulates For RCP4.5, the projected temperature is 24.67 C higher temperatures with larger standard deviations as ° ° ° (23.30 C) and 26.02 C (24.74 C) for the near and far fu- compared to the RCP4.5, particularly in the far future. ture, respectively, over the entire domain (Arabian Pen- Note that the past temperature for the entire domain from ° ° ° insula subdomain). In this case, the standard deviation is CRU (ERA-Int) is 24.49 C (24.34 C) and is 22.56 C and 21°W 21°W 21°W 14°W 14°W 14°W 7°W 7°W 7°W 0 0 0 7°E 7°E 7°E 14°E 14°E 14°E 21°E 21°E 21°E 28°E 28°E 28°E 35°E 35°E 35°E 42°E 42°E 42°E 49°E 49°E 49°E 56°E 56°E 56°E 63°E 63°E 63°E 70°E 70°E 70°E 21°W 21°W 21°W 14°W 14°W 14°W 7°W 7°W 7°W 0 0 0 7°E 7°E 7°E 14°E 14°E 14°E 21°E 21°E 21°E 28°E 28°E 28°E 35°E 35°E 35°E 42°E 42°E 42°E 49°E 49°E 49°E 56°E 56°E 56°E 63°E 63°E 63°E 70°E 70°E 70°E Advances in Meteorology 7 25 25 20 20 15 15 (a) (b) Figure 4: Box plots of RegCM4-simulated air temperature (in C) for each model for the past climate averaged over (a) 11 subdomains for the CORDEX-MENA/Arab domain and (b) subdomain over the Arabian Peninsula. )e temperature is averaged over the period 1980–2005. 23.13 C for the HadGEM2- and ECHAM6-driven runs, average from the beginning of the 2040s, for both RCP4.5 respectively (see Figure 4). Over the Arabian Peninsula and RCP8.5 (Figure 6). )e temperature anomaly was ob- ° ° subdomain, these values are 25.33 C (23.50 C) for CRU tained by adding the base period bias to the projection ° ° (ERA-Int) and 20.90 C and 22.39 C for HadGEM2- and period (hence called the corrected temperature) and then ECHAM6-driven runs, respectively. subtracting the average from each year. Irrespective of the For the RCP4.5 scenario, future changes in the simulated driving model, the RCP8.5 projected higher temperatures mean temperature (averaged from RegCM4-HadGEM2 and than RCP4.5 did. )e difference between RCP4.5 and RegCM4-ECHAM6) indicate a rise in the annual mean of RCP8.5 in the base period is due to the anomaly calculation around 2 C in the near future over the full domain, which (yearly value minus the average from 2071–2100) though the will accelerate to 4 C over the Arabian Peninsula in the far data for both scenarios are exactly the same for this period. future (Sup 2(a) and 2(b)). In the winter season, the pro- )e spread is for the daily average to obtain an annual value ° ° jected change in temperature will reach about 3 C (4 C) for for the different driving GCMs. Averages from RegCM4- HadGEM2 and RegCM4-ECHAM6 over the entire domain the near (far) future over the peninsula (Sup 2(c) and 2(d)). In the summer season, the rise in temperature will not indicate that temperature will increase significantly (at 95% ° ° ° exceed 2.5 (3.5 C) in the near (far) future over the Arabian level) at the rate of 0.73 (0.27), 0.59 (0.39), and 0.79 (0.20) C Peninsula (Sup 2(e) and 2(f)). Hence, the average data show per decade for RCP8.5 (RCP 4.5) during the periods a larger increase in the winter season temperature compared 2021–2100, 2021–2050, and 2071–2100, respectively. A to the summer season. similar increasing trend in temperature is projected for the For the RCP8.5 scenario, future changes in the simulated Arabian Peninsula subdomain. )e rate of increase in mean temperature (averaged from RegCM4-HadGEM2 and temperature for this subdomain is projected to be 0.72 RegCM4-ECHAM6) indicate a rise in the annual mean of (0.29), 0.60 (0.30), and 0.83 (0.25) C per decade for RCP8.5 ° ° around 2.5 C in the near future, which will accelerate to 6 C (RCP4.5) during the periods 2021–2100, 2021–2050, and over the Arabian Peninsula in the far future (Sup 3(a) and 2071–2100, respectively, which are significant at 95% level. 3(b)). For the same regions, the future change in temperature Hence, the rising trend in temperature for the RCP8.5 ° ° will reach about 4 C (7 C) for the near (far) future periods scenario in the far future is higher for the subdomain over during the winter season (Sup 3(c) and 3(d)). In the summer the Arabian Peninsula than over the entire domain because season, the rise in temperature over the Arabian Peninsula will the averaging filters out the peak temperatures in the entire be within 7 C (Sup 3(e) and 3(f)). Average data show a larger domain. )ese projected changes in temperature are useful increase in the winter season temperature compared to the in climate change impact studies and vulnerability, adap- summer season. )ese results support the statement that the tation (e.g., [48]) and drought studies (e.g., [49–51]). environment is warming while cold extremes warm faster than warm extremes by about 30 to 40% globally averaged [47]. Future changes in mean temperature (averaged over all 3.3. Hot Days and Cold Nights. )e projected number of subdomains) indicate that it will be above the 1971–2100 RegCM4-simulated hot days (T ≥ 50 C) is large in the max Temperature (°C) CRU RegCM4-ERA-Int RegCM4-HadGEM RegCM4-ECHAM Temperature (°C) CRU RegCM4-ERA-Int RegCM4-HadGEM RegCM4-ECHAM 8 Advances in Meteorology 35 35 30 30 25 25 20 20 (a) (b) 35 35 30 30 25 25 20 20 (c) (d) Figure 5: Box plots of RegCM4-simulated air temperature (in C) for each model and RCPs for near future and far future averaged over 11 subdomains for CORDEX-MENA/Arab domain (a, b) and subdomain over the Arabian Peninsula (c, d). )e Ens2RCP8.5 and EnsRCP4.5 represent the average from HadGEM and ECHAM for the RCP8.5 and RCP4.5, respectively. )e red boxes are for RCP8.5 and yellow boxes for RCP4.5. eastern region of the Arabian Peninsula and may reach in the far future. )ese results support previous studies about 120 days with RCP4.5 in the near future and above (e.g., [29]) which found that warming over the Arabian 130 days in the far future (Figures 7(a) and 7(b)). )e dis- Peninsula increased in the future and is larger for the RCP8.5 tribution pattern of hot days for the RCP8.5 case is very scenarios than for RCP4.5. )e European and African re- similar to the RCP4.5 case for the near future (Figure 7(c)). gions also show a decrease of cold nights in the far future and However, the area covered by more than 130 hot days in- a greater decrease for RCP8.5 than for RCP4.5, which in fact creased during the far future (Figure 7(d)). Within the indicates the warming. )e number of hot days is relatively low for RCP4.5 and analysis domain, the number of hot days will increase for the European regions in the far future and the greater increase large for RCP8.5, when averaged from RegCM4-HadGEM2 will be under the RCP8.5 scenario as compared to RCP4.5. and RegCM4-ECHAM6 for both the CORDEX domain and )e distribution pattern of cold nights (T ≤ 5 C) is almost the Arabian Peninsula subdomain (Figure 8). An increase in min opposite to the pattern for hot days (Figures 7(e)–7(h)). In hot days is projected after the 2040s and will be large for the this case, more cold nights are projected in the western Arabian Peninsula subdomain as compared to the CORDEX region of the Arabian Peninsula and the number of cold domain. For the entire domain, the rate of increase rate in nights is larger with RCP4.5 than with RCP8.5. In addition, a hot days is 1.19 and 8.01 days per decade for the RCP4.5 and higher cold night number is observed in the near future than RCP8.5 scenarios, respectively, during the period 2021– Temperature (°C) Temperature (°C) HadGEM8.5 HadGEM8.5 ECHAM8.5 ECHAM8.5 Ens2RCP8.5 Ens2RCP8.5 HadGEM4.5 HadGEM4.5 ECHAM4.5 ECHAM4.5 Ens2RCP4.5 Ens2RCP4.5 Temperature (°C) Temperature (°C) HadGEM8.5 HadGEM8.5 ECHAM8.5 ECHAM8.5 Ens2RCP8.5 Ens2RCP8.5 HadGEM4.5 HadGEM4.5 ECHAM4.5 ECHAM4.5 Ens2RCP4.5 Ens2RCP4.5 Advances in Meteorology 9 –2 –4 –6 RCP8.5 HadGEM&ECHAM6 RCP8.5 RCP4.5 HadGEM&ECHAM6 RCP4.5 (a) –2 –4 –6 RCP8.5 HadGEM&ECHAM6 RCP8.5 HadGEM&ECHAM6 RCP4.5 RCP4.5 (b) Figure 6: Changes in corrected temperature (base period temperature bias is added with each yearly value) for (a) CORDEX-MENA/Arab and (b) Arabian Peninsula subdomain for the period 1971–2100. Anomaly is obtained from any yearly value minus the average amount. Average is obtained from HadGEM2- and ECHAM6-driven runs for both RCP4.5 and RCP8.5. Shaded area shows the range and gray color indicates the past climate. 2100. For the Arabian Peninsula subdomain, the RCP4.5 decade) scenarios, while the rate of decrease is greater for (RCP8.5) projected hot days will increase at the rate of the Arabian Peninsula subdomain (−3.49 and −6.14 days 1.57 (11.40) days per decade. All the trends in numbers of per decade for RCP4.5 and RCP8.5, respectively) for the hot days are statistically significant at the 95% level. Note period 2021–2100 (Figure 9). All the decreasing trends are that the ERA-Int-driven data available for the period statistically significant at 95% level. )e decrease of cold 1979–2015 support the pattern of hot days obtained from nights means the warming which may relate to the climate RegCM4-HadGEM2 and RegCM4-ECHAM6. change in the region. For the cold nights, the average For the entire domain, there is a downward trend in the pattern from the HadGEM2- and ECHAM6-driven runs number of RegCM4-simulated cold nights for both RCP4.5 closely follows the pattern from the ERA-Int-driven run (−1.52 days per decade) and RCP8.5 (−2.95 days per during the available period. Temperature anomaly (°C) Temperature anomaly (°C) 1971 1971 1974 1974 1977 1977 1980 1980 1983 1983 1986 1986 1989 1989 1992 1992 1995 1995 1998 1998 2001 2001 2004 2004 2007 2007 2010 2010 2013 2013 2016 2016 2019 2019 2022 2022 2025 2025 2028 2028 2031 2031 2034 2034 2037 2037 2040 2040 2043 2043 2046 2046 2049 2049 2052 2052 2055 2055 2058 2058 2061 2061 2064 2064 2067 2067 2070 2070 2073 2073 2076 2076 2079 2079 2082 2082 2085 2085 2088 2088 2091 2091 2094 2094 2097 2097 2100 2100 10 Advances in Meteorology 45°N 45°N 130 130 40°N 40°N 120 120 110 110 35°N 35°N 100 100 30°N 30°N 90 90 25°N 25°N 80 80 70 70 20°N 20°N 60 60 15°N 15°N 50 50 10°N 40 10°N 40 30 30 5°N 5°N 20 20 EQ EQ 10 10 5°S 1 5°S 1 (a) (b) 45°N 45°N 130 130 40°N 120 40°N 120 110 110 35°N 35°N 100 100 30°N 30°N 90 90 25°N 80 25°N 80 70 70 20°N 20°N 60 60 15°N 15°N 50 50 10°N 40 10°N 40 30 30 5°N 5°N 20 20 EQ EQ 10 10 5°S 5°S 1 1 (c) (d) 45°N 45°N 130 130 40°N 40°N 120 120 110 110 35°N 35°N 100 100 30°N 30°N 90 90 25°N 25°N 80 80 70 70 20°N 20°N 60 60 15°N 15°N 50 50 10°N 10°N 40 40 30 30 5°N 5°N 20 20 EQ EQ 10 10 5°S 5°S 1 1 (e) (f) 45°N 45°N 130 130 40°N 40°N 120 120 110 110 35°N 35°N 100 100 30°N 30°N 90 90 25°N 25°N 80 80 70 70 20°N 20°N 60 60 15°N 15°N 50 50 10°N 10°N 40 40 30 30 5°N 5°N 20 20 EQ EQ 10 10 5°S 5°S 1 1 (g) (h) Figure 7: Spatial distribution of RegCM4-simulated hot days (T > 50 C) for (a) RCP4.5 near future, (b) RCP4.5 far future, (c) RCP8.5 max near future, and (d) RCP8.5 far future along with cold nights (T < 5 C) for (e) RCP4.5 near future, (f) RCP4.5 far future, (g) RCP8.5 near min future, and (h) RCP8.5 far future. Average is taken over HadGEM2- and ECHAM6-driven runs. )e near and future is 2021–2050 and 2071–2100, respectively. 21°W 21°W 21°W 21°W 14°W 14°W 14°W 14°W 7°W 7°W 7°W 7°W 0 0 0 0 7°E 7°E 7°E 7°E 14°E 14°E 14°E 14°E 21°E 21°E 21°E 21°E 28°E 28°E 28°E 28°E 35°E 35°E 35°E 35°E 42°E 42°E 42°E 42°E 49°E 49°E 49°E 49°E 56°E 56°E 56°E 56°E 63°E 63°E 63°E 63°E 70°E 70°E 70°E 70°E 21°W 21°W 21°W 21°W 14°W 14°W 14°W 14°W 7°W 7°W 7°W 7°W 0 0 0 0 7°E 7°E 7°E 7°E 14°E 14°E 14°E 14°E 21°E 21°E 21°E 21°E 28°E 28°E 28°E 28°E 35°E 35°E 35°E 35°E 42°E 42°E 42°E 42°E 49°E 49°E 49°E 49°E 56°E 56°E 56°E 56°E 63°E 63°E 63°E 63°E 70°E 70°E 70°E 70°E Advances in Meteorology 11 100 100 90 90 80 80 70 70 60 60 50 50 40 40 30 30 20 20 10 10 0 0 RCP4.5 RCP4.5 Had and ECHAM Had and ECHAM ERA-Int75 ERA-Int75 (a) (b) 100 100 90 90 80 80 70 70 60 60 50 50 40 40 30 30 10 10 RCP8.5 RCP8.5 Had and ECHAM Had and ECHAM ERA-Int75 ERA-Int75 (c) (d) Figure 8: Number of RegCM-simulated hot days (T ≥ 50 C) for (a) CORDEX domain with RCP4.5, (b) Arabian Peninsula subdomain max with RCP4.5, (c) CORDEX domain with RCP8.5, and (d) Arabian Peninsula subdomain with RCP8.5. Average is taken from HadGEM2- and ECHAM6-driven runs. Shaded area shows the range, and gray color indicates the past climate. 3.4. Projected Changes in Hot Days and Cold Nights. Average values from RegCM4-HadGEM2 and RegCM4- Changes in hot days and cold nights using RegCM4-driven ECHAM6 indicate an increasing (decreasing) number of hot by HadGEM2 and ECHAM6, and obtained for future cli- days (cold nights) over both the CORDEX domain and the mates relative to the base period, are shown in Figure 10. )e Arabian Peninsula (Figures 7 and 8). Decadal analysis in- number of hot days will rise to about 50 days more in the dicates that the number of hot days is 568 (706) in the decade desert region (Rub Al-Khali) over the Arabian Peninsula in 2091–2100 as compared to only 15 (184) in the decade the near future, with respect to the base period. )is will 2021–2030 for the entire domain (Arabian Peninsula sub- reach about 80 days more in the far future for the RCP4.5 domain) with RCP8.5 (Figure 11(a)). Decadal analysis also scenario (Figures 10(a) and 10(b)). In the case of the RCP8.5 displays a decreasing number of cold nights in the last scenario, the number of hot days will reach about 70 days decade (CORDEX/Arabian Peninsula, −310/−675) as more in the desert region (Rub Al-Khali) over the Arabian compared to the earlier decade (CORDEX/Arabian Penin- Peninsula in the near future, with respect to the base period. sula, −118/−278). Note that the values are negative, so an )is will rise to about 130 days more in the far future increased negative value means a decrease in the number of st (Figures 10(c) and 10(d)). At the end of the 21 century, over cold nights. )e rate of decrease over the Arabian Peninsula most parts of the Arabian Peninsula, the number of hot days is higher than that over the entire domain (Figure 11(b)). will be about 60 days more compared to the base period, )ese results further indicate a higher warming rate over the Arabian Peninsula as compared to the entire domain during although in the southwest hilly region, the projected number st is small. )e number of cold nights is expected to drop by a the 21 century. large amount in the northwest and by a smaller amount in the southeast areas of the Peninsula. )e rate of decrease of cold nights will be large in the far future as compared to the 3.5. Maximum Temperature at Some Major Cities in Saudi Arabia. From the above discussion, it is evident that the near future for both RCPs (Figures 10(e)–10(h)). Hence, the st northwest region of the Peninsula will face great warming, future climate over the Arabian Peninsula during the 21 century will be warming at a higher rate as compared to the due to the faster rate of decrease of cold nights at the end of st the 21 century. entire domain. To understand the real pattern of Frequency (days) Frequency (days) 1971 1972 1981 1982 1986 1987 1991 1992 1996 1997 2001 2002 2006 2007 2011 2012 2016 2017 2031 2032 Frequency (days) Frequency (days) 1961 1961 1966 1966 1971 1971 1986 1986 1991 1991 2006 2006 2096 12 Advances in Meteorology 100 100 90 90 80 80 70 70 60 60 50 50 40 40 30 30 20 20 10 10 0 0 RCP4.5 RCP4.5 Had and ECHAM Had and ECHAM ERA-Int ERA-Int (a) (b) 100 100 90 90 80 80 70 70 60 60 50 50 40 40 30 30 20 20 0 0 RCP8.5 RCP8.5 Had and ECHAM Had and ECHAM ERA-Int ERA-Int (c) (d) Figure 9: Number of RegCM-simulated cold nights (T ≤ 5 C) for (a) CORDEX domain with RCP4.5, (b) Arabian Peninsula subdomain min with RCP4.5, (c) CORDEX domain with RCP8.5, and (d) Arabian Peninsula subdomain with RCP8.5. Average is taken from HadGEM2- and ECHAM6-driven runs. Shaded area shows the range, and gray color indicates the past climate. temperature rise over the Arabian Peninsula, the RegCM4- 33.81 C from the RegCM4 simulation. In the case of Riyadh, simulated maximum temperature are extracted at 27 average temperature over the common period of 1985–2014 is ° ° meteorological station locations across Saudi Arabia (80% 33.29 C (36.75 C) from observations (ERA-Int), while it is coverage of the Peninsula) and compared with the me- 34.90 C from the RegCM4 simulation. Overall, the simulation teorological station data. )is exercise gives us confidence underestimates the maximum temperature for Makkah and in the performance of RegCM4 for the simulation of Madinah while overestimating it for Riyadh and for the temperature over the study region. Note that data available country as a whole, relative to the surface observations. )is from just one station in each city are taken as represen- indicates regional variations in temperature simulation using tative of the city for the purposes of this study. RegCM4 which depends on different factors including land )e patterns of maximum temperature at some major use and urbanization. )e two holly cities Makkah and ° ° ° cities such as Makkah (21.43 N, 39.79 E), Madinah (24.54 N, Madinah are well developed from the historical period where ° ° ° 39.70 E), and Riyadh (24.92 N, 46.72 E), as well as the average the model underestimated maximum temperature. )is is in over 27 stations across Saudi Arabia, obtained from RegCM4- line with the general cold bias by the RegCM4 [17]. On the simulated averages from HadGEM2 and ECHAM6, along other hand, the capital city Riyadh is expanding with new with ERA-Int-driven runs and surface observations, are shown infrastructures and development programs and rapid growth of in Figure 12. In general, the simulated maximum temperature urbanization where RegCM4 overestimates maximum tem- perature. )is is similar to the warm bias over Oman/Yemen as follows the pattern of observations closely. For Makkah and Madinah, the ERA-Int is very close to the observations reported in [17] and by Wang and Xubin (2013) which might (Figures 12(a) and 12(b)), while for Riyadh (Figure 12(c)), it is be due to some error or low dense network data coverage in the overestimated by around 3.5 C (Figure 12(d)). )e average observations. )erefore, this temperature underestimation by temperature of Makkah over the common period of 1985– the climate model at some locations and overestimation at ° ° 2014 is 38.26 C (38.55 C) from observations (ERA-Int) while it other locations are an unresolved issue and need further in- is 35.86 C from the RegCM4 simulation. For Madinah, the vestigation. Hence, model simulations can provide the overall average temperature over the common period of 1985–2014 is pattern of the observed maximum temperature at local scale. ° ° 35.21 C (35.66 C) from observations (ERA-Int) while it is However, bias varies from location to location and needs to be Frequency (days) Frequency (days) 1961 1961 1966 1966 1971 1971 1976 1976 1981 1981 1986 1986 1991 1991 1996 1996 2001 2001 2006 2006 2011 2011 2016 2016 2021 2021 2026 2026 2031 2031 2036 2036 2041 2041 2046 2046 2051 2051 2056 2056 2061 2061 2066 2066 2071 2071 2076 2076 2081 2081 2086 2086 2091 2091 2096 2096 Frequency (days) Frequency (days) 1961 1961 1966 1966 1971 1971 1976 1976 1981 1981 1986 1986 1991 1991 1996 1996 2001 2001 2006 2006 2011 2011 2016 2016 2021 2021 2026 2026 2031 2031 2036 2036 2041 2041 2046 2046 2051 2051 2056 2056 2061 2061 2066 2066 2071 2071 2076 2076 2081 2081 2086 2086 2091 2091 2096 2096 Advances in Meteorology 13 45°N 45°N 130 130 40°N 40°N 120 120 110 110 35°N 35°N 100 100 30°N 30°N 90 90 25°N 25°N 80 80 70 70 20°N 20°N 55 55 15°N 15°N 45 45 10°N 10°N 35 35 5°N 5°N 15 15 EQ EQ 5 5 5°S –1 5°S –1 (a) (b) 45°N 45°N 130 130 40°N 40°N 110 110 35°N 35°N 100 100 30°N 30°N 90 90 25°N 25°N 80 80 70 70 20°N 20°N 55 55 15°N 15°N 45 45 10°N 10°N 35 35 25 25 5°N 5°N 15 15 EQ EQ 5 5 5°S 5°S –1 –1 (c) (d) 45°N 45°N 40°N 40°N 9 9 3 3 35°N 35°N –3 –3 30°N 30°N –9 –9 25°N 25°N –15 –15 –21 –21 20°N 20°N –27 –27 15°N 15°N –33 –33 10°N –39 10°N –39 –45 –45 5°N 5°N –51 –51 EQ EQ –57 –57 5°S 5°S –65 –65 (e) (f) 45°N 45°N 15 15 40°N 40°N 9 9 3 3 35°N 35°N –3 –3 30°N 30°N –9 –9 25°N –15 25°N –15 –21 –21 20°N 20°N –27 –27 15°N 15°N –33 –33 10°N 10°N –39 –39 –45 –45 5°N 5°N –51 –51 EQ EQ –57 –57 5°S –65 5°S –65 (g) (h) Figure 10: Spatial distribution of changes in hot days (T > 50 C) for (a) RCP4.5 near future, (b) RCP4.5 far future, (c) RCP8.5 near future, max and (d) RCP8.5 far future along with cold nights (T < 5 C) for (e) RCP4.5 near future, (f) RCP4.5 far future, (g) RCP8.5 near future, and min (h) RCP8.5 far future with respect to the base period (1971–2000). Average is taken over HadGEM2- and ECHAM6-driven runs. 21°W 21°W 21°W 21°W 14°W 14°W 14°W 14°W 7°W 7°W 7°W 7°W 0 0 0 0 7°E 7°E 7°E 7°E 14°E 14°E 14°E 14°E 21°E 21°E 21°E 21°E 28°E 28°E 28°E 28°E 35°E 35°E 35°E 35°E 42°E 42°E 42°E 42°E 49°E 49°E 49°E 49°E 56°E 56°E 56°E 56°E 63°E 63°E 63°E 63°E 70°E 70°E 70°E 70°E 21°W 21°W 21°W 21°W 14°W 14°W 14°W 14°W 7°W 7°W 7°W 7°W 0 0 0 0 7°E 7°E 7°E 7°E 14°E 14°E 14°E 14°E 21°E 21°E 21°E 21°E 28°E 28°E 28°E 28°E 35°E 35°E 35°E 35°E 42°E 42°E 42°E 42°E 49°E 49°E 49°E 49°E 56°E 56°E 56°E 56°E 63°E 63°E 63°E 63°E 70°E 70°E 70°E 70°E 14 Advances in Meteorology T ≥ 50°C max 2021– 2031– 2041– 2051– 2061– 2071– 2081– 2091– 2030 2040 2050 2060 2070 2080 2090 2100 CORDEX Arabian Peninsula (a) T ≤ 5°C min 2021– 2031– 2041– 2051– 2061– 2071– 2081– 2091– 2030 2040 2050 2060 2070 2080 2090 2100 CORDEX Arabian Peninsula (b) ° ° Figure 11: Decadal variations of the number of hot days (T ≥ 50 C) and cold nights (T ≤ 5 C) with respect to the reference period max min (1971–2000) obtained from average of HadGEM2- and ECHAM6-driven runs under RCP8.5 for (a) CORDEX-MENA/Arab domain and (b) Arabian Peninsula subdomain. st considered when using the model data in application-oriented end of the 21 century. Based on Figure 12, the maximum tasks such as heat index calculations. )e model-simulated temperature simulations based on the RCP8.5 (RCP4.5) relative humidity for each panel indicates an insignificant rate scenarios show the following features at some major cities in of decrease. )is indicates that because the temperature will Saudi Arabia: increase in the future, warmer air’s larger capacity to store (i) At Makkah, the maximum temperature increase water vapor may cause decrease of relative humidity. rate is projected to be 0.51 (0.30), 0.60 (0.28), and For all station averages, the simulations reveal similar 0.76 (0.06) C per decade for the periods 1961–2100, patterns for both the RCP8.5 and RCP4.5 scenarios until the 2021–2050, and 2071–2100, respectively mid-2030s. After that, the RCP8.5-based projections deviate to higher values compared to those of RCP4.5. )e difference (ii) At Madinah, the maximum temperature increase between projected values for the two RCPs is about 3 C at the rate is projected to be 0.54 (0.34), 0.57 (0.34), and Changes in frequency (days/decade) Changes in frequency (days/decade) –118 15 –278 184 –137 28 –310 244 –179 56 –420 360 –200 108 –419 367 –226 216 –514 497 –272 324 –605 –290 442 –651 622 –310 568 –675 706 Advances in Meteorology 15 42 70 42 70 40 60 40 60 38 50 38 50 36 40 36 40 34 30 34 30 32 20 32 20 30 10 30 10 28 0 28 0 RCP8.5 RCP4.5 RCP8.5 RCP4.5 Had and ECHAM Had and ECHAM Had and ECHAM Had and ECHAM ERA–Int Obs ERA–Int Obs RH4.5 RH8.5 RH4.5 RH8.5 (a) (b) 42 70 42 70 40 60 40 60 38 50 38 50 36 40 36 40 34 30 34 30 32 20 32 20 30 10 30 10 28 0 28 0 RCP8.5 RCP4.5 RCP8.5 RCP4.5 Had and ECHAM Had and ECHAM Had and ECHAM Had and ECHAM ERA–Int Obs ERA–Int Obs RH4.5 RH8.5 RH4.5 RH8.5 (c) (d) Figure 12: Simulated maximum temperature extracted nearer grid point of the station locations for (a) Makkah, (b) Madinah, (c) Riyadh, and (d) Saudi Arabia (averaged over 27 stations) for both RCP4.5 and RCP8.5 along with ERA-Int and surface observational data. For RegCM simulations, average taken from HadGEM2- and ECHAM6-driven runs are also shown by solid lines. Shaded area shows the range. )e relative humidity (in %) is also shown for each panel (RH85 and RH45 for, respectively, RCP8.5 and RCP4.5). 0.66 (0.03) C per decade for the periods 1961–2100, 4. Conclusions 2021–2050, and 2071–2100, respectively st In this study, the change in temperature in the 21 century (iii) At Riyadh, the maximum temperature increase rate over the CORDEX-MENA domain with a focus on the is projected to be 0.59 (0.38), 0.70 (0.27), and 0.69 Arabian Peninsula has been projected from RegCM4 sim- (0.15) C per decade for the periods 1961–2100, ulations. Data from the three CMIP5 models HadGEM2, 2021–2050, and 2071–2100, respectively ECHAM6, and CanESM were downscaled with RegCM4 (iv) Over Saudi Arabia, the maximum temperature (RegCM4-HadGEM2, RegCM4-ECHAM6, and RegCM4- increase rate is projected to be 0.59 (0.41), 0.63 CanESM). )e RegCM4-CanESM variant largely over- (0.29), and 0.67 (0.10) C per decade for the pe- estimated the mean temperature in the past climate and was riods 1961–2100, 2021–2050, and 2071–2100, found to be not useful in climate projection over the analysis respectively domain. )e maximum temperatures extracted at few main )e increase rates for the above three stations, and cities in Saudi Arabia were also projected. )e analysis included two RCPs scenarios, namely, RCP4.5 and RCP8.5. averaged over all stations, are significant at the 95% level. Overall, the simulated maximum temperature follows the In general, the RegCM4 simulations with RCP8.5 were likely to project a warmer climate than those conducted with pattern of observations. However, caution is recommended before the use of model temperature for application- RCP4.5. )e RCP8.5 scenario projected a temperature in- oriented tasks which vary from location to location. crease of about 7 C over the Arabian Peninsula by the end of st )erefore, the uncertainty at each location must be con- the 21 century. )is increase in temperature is more sidered for climate change impact studies using model data. pronounced during the winter season than during the Further study may require using data from the newly summer. Over the entire domain, the temperature is pro- developed Saudi-KAU Global Climate Model and focusing jected to increase at the rate of 0.73 (0.27), 0.59 (0.39), and 0.79 (0.20) C per decade under RCP8.5 (RCP4.5) scenarios, on the simulation of climate over the Arabian Peninsula [52–54]. for the periods 2021–2100, 2021–2050, and 2071–2100, T (°C) T (°C) max max 1965 1965 1973 1973 1981 1981 1985 1985 1989 1989 1993 1993 1997 1997 2001 2001 2005 2005 2009 2009 2013 2013 2017 2017 2021 2021 2025 2025 2029 2029 2033 2033 2037 2037 2041 2041 2045 2045 2049 2049 2053 2053 2057 2057 2061 2061 2065 2065 2069 2069 2073 2073 2077 2077 2081 2081 2085 2085 2089 2089 2097 2097 RH (%) RH (%) T (°C) T (°C) max max 1961 1961 1965 1965 1969 1969 1973 1973 1977 1977 1981 1981 1985 1985 1989 1989 1993 1993 1997 1997 2005 2005 2009 2009 2013 2013 2017 2017 2021 2021 2025 2025 2029 2029 2033 2033 2037 2037 2041 2041 2045 2045 2049 2049 2053 2053 2057 2057 2061 2061 2065 2065 2069 2069 2073 2073 2077 2077 2081 2081 2085 2085 2089 2089 2093 2093 2097 2097 RH (%) RH (%) 16 Advances in Meteorology respectively. )e rate of increase in temperature over the Supplementary Materials Arabian Peninsula subdomain is projected to be 0.72 (0.29), Sup 1: distribution of air temperature (in C) obtained from 0.60 (0.30), and 0.83 (0.25) C per decade under the RCP8.5 (a) annual CRU, (b) annual ERA-Int, (c) winter CRU, (d) (RCP4.5) scenario, for the periods 2021–2100, 2021–2050, winter ERA-Int, (e) summer CRU, and (f) summer ERA-Int and 2071–2100, respectively. )e RCP8.5-projected hot ° averaged for the common period 1980–2005. )e 11 sub- days (T ≥ 50 C) are likely to increase at the rate of 8.01 max domains are drawn following Almazroui (2016) and aver- (11.40) days per decade, while the decrease in cold nights aged over these subdomains represent the CORDEX- (T ≤ 5 C) is projected to be −2.95 (−6.14) nights per min MENA/Arab domain used for objective analysis later on. decade for the CORDEX (Arabian Peninsula) domain. All Sup 2: spatial distribution of changes in RegCM4-simulated increasing trends in temperature and in hot day numbers mean temperature under RCP4.5 for (a) annual near future, and decreasing trends in cold nights are statistically sig- (b) annual far future (top right), (c) winter season near nificant at the 95% level. )ese provide a clear indication of future, (d) winter season far future, (e) summer season near a warming climate in the future over the Arabian Penin- future, and (f) summer season far future. Data are averaged sula, even if the warming may vary from region to region. from HadGEM2- and ECHAM6-driven runs. )e change is )e projected warming rate over the Arabian Peninsula is calculated as average of near (or far far) future minus the larger than that over the entire domain. )e RegCM4-based base period value. Sup 3: changes in RegCM4 mean tem- temperature follows the pattern of surface observations at perature ( C) in the future climate under RCP8.5 with re- the station level across Saudi Arabia. )erefore, spect to the base period (1971–2000) for (a) annual near HadGEM2- and ECHAM6-driven runs are recommended future, (b) annual far future, (c) winter season near future, as input databases for environmental vulnerability as- (d) winter season far future, (e) summer season near future, sessment studies since the CanESM output was found to be and (f) summer season far future. Data are averaged from unsuitable. However, more CMIP5 models may be eval- HadGEM2- and ECHAM6-driven runs. (Supplementary uated for their utility in application-oriented tasks in Materials) further studies. Data Availability References )e data are run in the supercomputer of the King [1] Y. K. 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