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Numerical Simulation of the Effects of Grassland Degradation on the Surface Climate in Overgrazing Area of Northwest China

Numerical Simulation of the Effects of Grassland Degradation on the Surface Climate in... Hindawi Publishing Corporation Advances in Meteorology Volume 2013, Article ID 270192, 9 pages http://dx.doi.org/10.1155/2013/270192 Research Article Numerical Simulation of the Effects of Grassland Degradation on the Surface Climate in Overgrazing Area of Northwest China 1 1 2,3,4 1 3,4 Yanfei Li, Zhaohua Li, Zhihui Li, Xiaoli Geng, and Xiangzheng Deng FacultyofResources andEnvironmental Science, HubeiUniversity, Wuhan, Hubei430062, China University of Chinese Academy of Sciences, Beijing 100049, China Institute of Geographic Science and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China Center for Chinese Agricultural Policy, Chinese Academy of Sciences, Beijing 100101, China Correspondence should be addressed to Xiangzheng Deng; dengxz.ccap@gmail.com Received 17 July 2013; Accepted 26 September 2013 Academic Editor: Burak Guneral ¨ p Copyright © 2013 Yanfei Li et al. 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. The climatic effects of LUCC have been a focus of current researches on global climate change. eTh objective of this study is to investigate climatic eeff cts of grassland degradation in Northwest China. Based on the stimulation of the conversion from grassland to other land use types during the next 30 years, the potential effects of grassland degradation on regional climate in the overgrazing area of NorthwestChinafrom2010to2040havebeenexploredwithWeather Research andForecasting model(WRF).Theanalysis results show that grassland will mainly convert into barren land, croplands, and urban land, which accounts for 42%, 48%, and 10% of the total converted grassland area, respectively. eTh simulation results indicate that the WRF model is appropriate for the simulation of the impact of grassland degradation on climate change. eTh grassland degradation during the next 30 years will result in the decrease of latent heat ux, fl which will further lead to the increase of temperature in summer, with an increment of 0.4–1.2 C, and the decrease of temperature in winter, with a decrement of 0.2 C. In addition, grassland degradation will cause the decrease of precipitation in both summer and winter, with a decrement of 4–20 mm. 1. Introduction and so forth, [7, 8]. eTh refore, it is of great signicfi ance to study the eeff cts of LUCC on regional climate for adapting The influence of human activities on the climate system to climate change. has become the focus of the academic community at home Grasslandasone of themostwidespreadlanduse type andabroadinthe context of global warmingsince the20th covers about 40% of the total land area of China [9, 10]. century [1]. The fourth assessment report of Intergovern- eTh grasslands provide various ecosystem services such as mental Panel on Climate Change (IPCC AR4) indicated that the provision of the forage, milk, and meat. Besides, the the human activities are an important influencing factor of grasslands also providesomeimportant ecosystemservices climate change, accounting for 90% of global warming [2, that regulate the regional climate, for example, the mitigation 3]. Some previous researches have showed that the human- of greenhouse gas (GHG) emissions through soil organic induced land use/land cover change (LUCC) was one of carbon (C) and nitrogen (N) sequestration [11, 12]. eTh refore, the major factors, which inu fl ence the regional climate [ 4]. the grassland change would be the import factor influencing The LUCC influences the climate change mainly through theclimatechange.TheovergrazingareasinNorthwestChina changing the underlying surface properties such as the are the most significant hinterlands. The grassland degra- surface reflectivity, roughness, soil moisture, leaf area, and dation and desertification in overgrazing area of Northwest vegetation coverage [5, 6]. eTh eeff cts of LUCC on the bio- China has greatly intensified due to the irrational exploitation geophysical processes vary from region to region, which are of the natural resources, rapid population growth, and the closely related with the land-atmosphere interaction, regional expansion of road network in recent years [13, 14]. The mean surface climate, environmental background and vegetation, rate of grassland degradation has accelerated overall in the 2 Advances in Meteorology ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 70 E 80 E 90 E 100 E 110 E 120 E 130 E 140 E 105 E 108 E 111 E 114 E Heilongjiang Jilin Inner Mongolia Xinjiang Liaoning Gansu Beijing Tianjin Hebei Shanxi Ningxia Shandong Qinghai Shaanxi Henan Jiangsu Tibet AnhuiShanghai Hubei Sichuan Chongqing Zhejiang Hunan Jiangxi Guizhou Fujian Taiwan Yunnan Guangxi Guangdong (km) Hainan 0 1,050 2,100 ∘ ∘ ∘ 105 E 108 E 111 E Cultivated land Water area ∘ ∘ ∘ ∘ Built-up area Forestry area 90 E 100 E 110 E 120 E Grassland Unused aera Figure 1: Location of the study area and the distribution of land use type in the overgrazing areas of Northwest China. past 50 years and only decelerated in recent years. Moreover, advances of RCMs and is specifically designed for high the grassland degradation has led to the decline of grassland resolution applications and provides an ideal tool for assess- productivity and increased the frequency of extreme climate ing the value of high resolution regional climate modeling, events such as droughts and er fi ce freeze-up, which have and some researchers have identified the WRF model to seriously inu fl enced the sustainable development of animal be superior to other RCMs such as RegCM2, RegCM3, husbandry [14]. eTh refore, it is of great importance to study RAMS, RIEMS, RegCM-NCC, and IPCR-RegCM [1, 25, theinufl enceofgrassland degradation on theclimate in the 26]. overgrazing area of Northwest China. Some studies with the WRF model have shown that eTh re have been many researches focusing on the grassland degradation in overgrazing areas of Northwest impacts of the grassland degradation in overgrazing areas China has obvious eeff ct on the regional climate [ 19, 24]. in Northwest China on climate change. Most of those However, those previous researches about the effects of researches detected the interaction between the grassland grassland degradation on the climate change have generally degradation and the climate change by the selection of focusedonthe eeff cts of land change during thehistorical regional climate model (RCMs) or global climate models period with the numerical simulation models, while there (GCMs) and experiment designs [15]. Xue and Fu et al. were few researches on the impacts of predicted future land identified that grassland degradation over the Mongolian usechangeonthe climate. eTh refore,thisstudy aims to and the Inner Mongolian grassland could bring signicfi ant estimate the potential impacts of grassland degradation on influence on surface climate [ 16, 17]. Zhang et al., found climate change in overgrazing area of Northwest China from that the grassland degradation could lead to the decrease 2010 to 2040 with the WRF model. of precipitation and the increase of surface temperature in Northwest China [18]. Liu et al. found that the grass- land desertification can lead to grand temperature increase 2. Data and Methodology in thedaytime anddecreaseatnight,and thesensitive 2.1. Study Area. The overgrazing area of Northwest China heat u fl x increase and the latent heat ux fl decrease in the ∘ 󸀠 ∘ 󸀠 ∘ 󸀠 ∘ 󸀠 is located in 104 04∼114 02 E, 32 40∼41 20 Nwithatotal Source Regions of Three Rivers [ 19]. All of these previous land area of 811856 km covering five provinces which include researches with GCMs and RCMs have contributed to the Ningxia Province, the south east part of Gansu Province, comprehensive understanding of the impacts of grassland Shaanxi Province, the west part of Shanxi Province, and the change on the climate change at the regional and global middle and south west part of Inner Mongolia Autonomous scales. However, because of the coarse resolution, there Region (Figure 1). It is one of the largest grazing areas of are some bias and uncertainties in the simulation of the regional climatechangewithGCMs[20–24]. The weather China, which is the major production base of the animal Research and Forecasting (WRF) model represents the recent husbandry industry in China. ∘ ∘ ∘ ∘ ∘ 10 N 20 N 30 N 40 N 50 N ∘ ∘ ∘ ∘ 20 N 30 N 40 N 50 N ∘ ∘ ∘ 33 N 36 N 39 N ∘ ∘ ∘ 33 N 36 N 39 N Advances in Meteorology 3 This region stretches across the eastern monsoon region Table 1: Parameterization scheme of physical processes in the WRF model. and northwest arid region and is close to the Qinghai- Tibet alpine region, approximately located in the transition Classification of schemes Scheme option zone of the three major natural zones of China. It is the Physics parameterization scheme WSM3-class simple ice continental semiarid climate in this region, with an annual Cumulus parameterization scheme Grell-Devenyi ensemble average temperature of 5–10 C and the annual precipitation Boundary layer process scheme YSU of 200–800 mm. There is very limited water resource, the Radiation scheme CAM 3 radiation spatiotemporal distribution of which is very imbalanced, and Land surface process scheme Noah land surface model there are frequently meteorological disasters. The grassland and cultivated land are the dominant land use types in this region, accounting for 36.19% and 29% of the total area, respectively. The irrational utilization of 2.3. Description of the WRF Model. The WRF model is grassland resources is very common due to overgrazing and a next-generation forecast model developed by the scien- overreclamation under the inu fl ence of pursuit of economic ticfi research center, atmospheric administration (NOAA), benefit since the 1980s. It has led to the continual degradation research institutions and universities in the United States. of the grassland. eTh proportion of grassland accounting Two motive power cores were included in the WRF model, forthe totalareaofNorthwest Chinahas decreasedfrom that is, ARW (Advanced Research WRF) developed by NCAR about36% in 1995 to 31%in2008, andmostofgrassland and used in scienticfi research and nonhydrostatic Mesoscale degradedintobarrenlandand croplands. eTh intensive Model (MMM) developed by NCEP and widely used in the grassland degradation has resulted in more and more acute business system. This study has mainly used the ARW model contradiction between the human and nature, economic [28]. development and eco-environmental conservation in region. The parameterization scheme of physical processes in Therefore, the exploration of the degree and mechanism of the WRF model in this study is as follows (Table 1). It grassland degradation’s influence on regional climate and mainly includes the WSM3-Class simple ice physical scheme, environment is of great significance to the policy making of ensemble cumulus convection schemes of Grell-Devenyi the regional sustainable land use and management. ensemble, YSU, CAM3 radiation schemes, and consolidated NOAH land surface parameterization scheme [29, 30]. 2.2. Data Resource. In this study, the 1 km resolution land 2.4. Test Design. In this study, two numerical simulation cover data of United States Geological Survey (USGS) clas- tests, including the control test and sensitivity test, were sification in 2010 were extracted from the MODIS dataset. designed and performed with the same horizontal resolu- The land conversion data with 1 km resolution used to tion and parameterization scheme in order to analyze the forecast the information of land use change (land conversion effects of grassland degradation on the regional climate more among different land cover types) during 2010–2040 were accurately, unlike other previous experiment studies in which simulated based on Representative Concentration Pathways the entire grassland was replaced by other land covers. eTh 6.0 (RCP6.0) using the Asia-Pacific Integrated Model (AIM) control test as a reference case used the land cover data of developed by the National Institute of Environmental Stud- 2010, while the sensitivity test used the land cover data from ies (NIES) in Japan. According to the requirement of the 2010 to 2040, in which part of grassland converted into bare WRF model, it is necessary to convert the 1 km resolu- land, croplands, and urban land. The climate forcing data tion land cover data of United States Geological Survey in both the control test and sensitivity test were all from (USGS) classification in 2010 into the 30 km resolution 2010 to 2040. eTh center of the simulated area is located data. ∘ 󸀠 ∘ 󸀠 ∘ at 37 53 N, 109 1 E with two standard parallels of 39 Nand The meteorological data used in this study, including 35 N, including 27 grid points in the east-west direction and the near-surface temperature and precipitation, were all 48 grid points in the north-south direction. The simulation from 84 meteorological stations in Ningxia Province, Inner period is 30 years from January 1st, 2010, to December 31th, Mongolia Autonomous Region, Gansu Province, Shanxi Province, and Shaanxi Province. In order to analyze the simulation accuracy of the WRF model, the original data of annual average temperature, monthly average temperature 3. Result and annual precipitation in year 2010 were interpolated into 1 km resolution grid data with the Kriging interpo- 3.1. Forecast of Future Grassland Degradation in Overgrazing lation method and then compared with the simulation Areas of Northwest China during 2010–2040. The grassland results. in the study mainly concentrates in the south and middle The atmospheric forcing data such as air temperature, part of Inner Mongolia and Ningxia Province, the northeast specific humidity, sea level pressure, eastward wind, north- of Gansu Province, and south part of Shaanxi Province, ward wind, and geopotential height from 2010 to 2040 accounting forabout 35%ofthe totalareaofovergrazing used in this study were from a state-of-the-art multimodel areas in Northwest China. This study stimulates the grassland dataset produced by the h phase of the Coupled Model change of overgrazing areas in Northwest China from 2010 Intercomparison Project (CMIP5) [27]. to 2040. eTh stimulation result indicated that with the fift 4 Advances in Meteorology ∘ ∘ ∘ ∘ ∘ change in the overgrazing areas of Northwest China since the 106 E 108 E 110 E 112 E 114 E performance of the WRF model in different regions may vary greatly. In this study, the simulation ability of WRF model was 40 N tested through comparing the stimulated temperature and 40 N precipitation with the observation data. eTh result indicates that the WRF model can simulate the temporal change of temperature very well (Figures 3(a) 38 N and 4(a)). According to the monthly temperature change in 38 N theentirestudy area,the simulatedtemperature is roughly consistent with the observed value in the spring and winter, ∘ ∘ and the difference between them ranges from 0 Cto0.5 C 36 N ∘ (Figure 3(a)). However, the temperature is obviously lower 36 N than the observed value in both the summer and autumn, with the dieff rence between them ranging from 0.5 Cto 2.5 C. As canbeseenfromFigure 4(a),the stimulated annual 34 N average temperature is lower than the observed value, and 34 N ∘ ∘ the difference between them ranges from 0.2 Cto1.4 C, indicating that there is only slight difference between the stimulated and observed annual average temperature. ∘ ∘ ∘ ∘ 106 E 108 E 110 E 112 E As canbeseenfromFigure 3(b), the stimulated precip- itationinthe spring andautumnof2010islower than the Barren or sparsely vegetated land observed value, and the difference between them ranges from Urban and built-up land 5mmto40mminmostmonthsexceptJune. Figure 4(b) Dryland cropland and pasture reveals that the annual precipitation of 2010 in overgrazing Grassland Others areas in Northwest China, especially the southeast part of Grassland converts to barren or sparsely vegetated land Gansu Province and northwest of Shaanxi Province, is lower Grassland converts to dryland cropland and pasture than the observed value, and the dieff rence between them Grassland converts to urban and built-up land generally ranges from 5 mm to 30 mm. In summary, the difference between the simulated and observed monthly and Figure 2: Conversion from grassland to other land use types annual change of precipitation is not very obvious. eTh refore, between 2010 and 2040 of the overgrazing areas in Northwest China. the WRF model can well simulate the monthly and annual change of precipitation very well. increasing population and unreasonable use of the grassland, 3.3. Eeff cts of Grassland Degradation on Latent Heat Flux. The the grassland degradation is still severe, in the future 30 years; land cover change can influence the energy balance of the the conclusion will be coherent with that of previous study earth-gas system through changing the underlying surface [31]. There will be mainly the conversion between grassland parameters such as the land surface albedo, roughness, and and croplands, bare land, and urban land. soil water content [26]. Latent heat u fl x is the indispens- This study also statistically analyzed the number of grid able element of energy exchange between land surface and cells converting from grassland into other land types between atmosphere [32]. The grassland degradation could decrease 2010 and 2040. The result indicates that there will be 55 the roughness, which would lead to the decrease of latent grids converting from grassland into other land types from heat exchange in the earth-gas system. As can be seen from 2010 to 2040 in the study area (Figure 2). About 48% of Figure 5, the grassland degradation would result in the the converted grassland will convert into croplands, which obvious decrease of the average monthly latent heat u fl x from mainly distributed in the southeast part of Inner Mongolia March to July, and the maximum decrement reaches about Autonomous Region, northwest part of Shaanxi Province, 10 W/m . and northeast part of Gansu Province. eTh obvious con- version from grassland into barren land will mainly occur in south and central part of Inner Mongolia and Shanxi 3.4. Effects of Grassland Degradation on the Land Surface Tem- Province, south part of Ningxia Province, and southeast part perature. The land use/cover change influences the regional of Gansu Province, accounting for 42% of the total number surface temperature through altering the land roughness, and of converted grids. er Th e will be 9 grids converting from soil hydrological and thermal features, which lead to further grassland into urban land, accounting for about 10% of the change of the land surface energy balance, long wave radia- total number of converted grids. In summary, the grassland tion, ux fl es of momentum, sensible heat and latent heat, and in overgrazing areas in Northwest China will mainly convert so forth [33]. While the impacts of grassland degradation on into barren land and croplands. the temperature in overgrazing areas of Northwest China can be analyzed through calculating the dieff rence in the annual 3.2. Result of the Control Test. It is necessary to investigate average near-surface temperature (air temperatures at two whether the WRF model can well simulate the climate meters above the ground) between the results of the control Advances in Meteorology 5 30 2.5 1400 50 25 45 1.5 0.5 123456789 10 11 12 −5 −10 −0.5 0 0 123456789 10 11 12 Observed Observed Simulated Simulated Observed-simulated Observed-simulated (a) (b) Figure 3: Difference between the observed and simulated monthly temperature ((a), unit: C) and precipitation ((b), unit: mm) of 2010 in the overgrazing areas of Northwest China. ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 106 E 108 E 110 E 112 E 106 E 108 E 110 E 112 E Inner Mongolia Inner Mongolia Shanxi Shanxi Ningxia Ningxia Shaanxi Shaanxi Gansu Gansu Henan Henan Hubei Hubei Sichuan Sichuan ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 106 E 108 E 110 E 112 E 106 E 108 E 110 E 112 E <− 30 −20–15 < − 1.4 −1.0–0.6 −1.4–1.0 > − 0.2 −30–25 −15–10 −25–20 >− 5 (a) (b) Figure 4: Difference between the simulated and observed annual average temperature ((a), unit: C) and annual precipitation ((b), unit: mm) in the overgrazing areas of Northwest China in 2010. test and sensitivity test on the basis of the simulation in the winter in the middle part of Inner Mongolia Autonomous control test and sensitivity test, the simulation result indicates Region, southwest of Ningxia Province, and northwest of that there will be different climate effects of the grassland Shanxi Province due to the conversion from grassland to degradation in different areas and seasons from 2010 to 2040 barren land and urban land with the decrement reaching in the overgrazing areas of Northwest China (Figure 6). 0.2 C(Figure 6(a)). Although the near-surface temperature Besides, the results of the two tests showed that the grassland of the winter increased in the middle part of Shaanxi Province degradation wouldincreasethe land surfacealbedo, which and north part of Shanxi Province due to the decrease of could lead to the decrease of near-surface temperature in the land surfacealbedocausedbyconversionfromgrassland to Observed/stimulated value ( C) ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N ∘ ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N Observed-stimulated value ( C) ∘ ∘ ∘ ∘ Observed/stimulated value (mm) 34 N 36 N 38 N 40 N ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N Observed-stimulated value (mm) 6 Advances in Meteorology 123456789 10 11 12 Control experiment Sensitive experiment Figure 5: Average monthly change of latent heat flux (unit: W/m ) in the overgrazing area of Northwest China from 2010 to 2040. ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 106 E 108 E 110 E 112 E 106 E 108 E 110 E 112 E Inner Mongolia Inner Mongolia Shanxi Shanxi Ningxia Ningxia Shaanxi Shaanxi Gansu Gansu Henan Henan Hubei Hubei Sichuan Sichuan ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 106 E 108 E 110 E 112 E 106 E 108 E 110 E 112 E < − 0.2 < − 0.4 0.8–1.2 0.4–0.6 −0.2–0 0–0.4 >1.2 >0.6 0.2–0.4 0.4–0.8 (a) (b) Figure 6: Difference in the annual average temperature (unit: C) in the winter (a) and summer (b) from 2010 to 2040 in the overgrazing areas in Northwest China between the sensitivity test and the control test. croplands, the grassland degradation can mainly result in and middle part of Shaanxi, which are in the overgrazing the decrease of the near-surface temperature of winter in the areas of Northwest China, with the increment of about study area. 1.2 C. The impacts of grassland degradation on the near- Although surface temperature of summer decrease in the surface temperature are more complicated and widespread southpartofInner Mongolia,the southpartofShaanxi in the summer than that in the winter. eTh grassland Province, and south east of Gansu Province with the drop degradation candecreasethe surfacealbedo, whichwill scale of about 0.4 C(Figure 6(b)), which would be caused result in the increase of the near-surface temperature in by the conversion from grassland to croplands since there is the overgrazing areas of Northwest China, with an incre- obvious difference between the surface albedo of croplands ∘ ∘ ment of about 0.4 C–1.2 C(Figure 6(b)). The temperature and grassland and the higher evapotranspiration of the crop- rise most obviously in the southwest of Inner Mongolia lands, the grassland degradation would mainly lead to the ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N Latent heat flux (W/m ) ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N Advances in Meteorology 7 ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 106 E 108 E 110 E 112 E 106 E 108 E 110 E 112 E Inner Mongolia Inner Mongolia Shanxi Shanxi Ningxia Ningxia Shaanxi Shaanxi Gansu Gansu Henan Henan Hubei Hubei Sichuan Sichuan ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 106 E 108 E 110 E 112 E 106 E 108 E 110 E 112 E <− 12 4–8 <− 20 −12–8 >8 >− 4 0–4 −20–16 −16–12 (a) (b) Figure 7: Difference in the annual precipitation (unit: mm) in the winter (a) and summer (b) from 2010 to 2040 in overgrazing areas of Northwest China between the sensitivity test and control test. increase of surface temperature of summer in the overgrazing China will make the climate change show a dry-warm trend areas of Northwest China. according to the results of both the control test and sensitivity test. eTh results are consistent with theoretical analysis results that the vegetation degradation will cause the increase of 3.5. eTh Eeff ctofGrassland DegradationonPrecipitation. The surfacealbedo, surfacesensibleheat, andthe decrease of land cover change can influence the precipitation through latent heat and thereby lead to the decrease of precipitation modifying both the energy balance and water balance [26, and increase of temperature [34]. 33]. There are very complex impacts of grassland degradation on the precipitation. Due to the complicated interactions between land surface and atmosphere, such as the inter- 4. Conclusion and Discussion actions between land surface albedo, soil moisture, sand temperature, the grassland degradation will increase surface Basedonthe analysis of grasslandchangeinthe future,this albedo, reduce roughness, and weaken the regulation func- study analyzed the impacts of grassland degradation on the tion of vegetation cover in the water cycle [26]. regional climate in the overgrazing areas of Northwest China The simulation result indicates that the grassland degra- through implementing the numerical simulation with the dation can cause the decrease of precipitation in the winter WRF model. eTh conclusions of this study are as follows. in most part of the overgrazing areas of Northwest China, eTh resultindicatesthattheWRFmodelcanwellsimulate with a decrement from about 0 mm to 12 mm (Figure 7(a)). the spatial pattern and change of temperature and precipi- Particularly, the annual precipitation in the northwest part tation, although the simulated value is a bit lower than the of Shanxi Province and south part of Inner Mongolia observed value. Besides, the grassland of Northwest China Autonomous Region will decline most obviously due to would mainly degrade into croplands, bare land, and urban the serious grassland desertification, with a decrement of land over the next 30 years. The most obvious grassland about 12 mm. Besides, in the summer, the conversion from change will occur in the central part of Inner Mongolia grassland to barren land can result in the obvious decrease Autonomous Region and northwest part of Shaanxi Province. of precipitation in north and central part of Shanxi Province, The simulation result indicates that the grassland degra- north part of Inner Mongolia, and Ningxia Province, with the dation will make the climate change in the overgrazing areas decrement ranging from about 4 mm to 20 mm (Figure 7(b)). of Northwest China show a dry-warm trend in the future The abovementioned numerical simulation of tempera- 30 years. The grassland degradation will lead to the decrease ture and precipitation in the next 30 years shows that the of latent heat flux through influencing the phase change of grassland degradation in the overgrazing areas of Northwest water in the atmosphere and the surface-airheatexchange. ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N 8 Advances in Meteorology The impacts of grassland degradation on the climate will [8] J.Jin andL.Wen,“Evaluation of snowmelt simulation in the weather research and forecasting model,” Journal of Geophysical vary in dieff rent seasons. In the summer, the grassland Research,vol.117,2012. degradation will lead to the increase of surface temperature [9] T. Akiyama and K. Kawamura, “Grassland degradation in and decrease of precipitation. 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Numerical Simulation of the Effects of Grassland Degradation on the Surface Climate in Overgrazing Area of Northwest China

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Copyright © 2013 Yanfei Li et al. 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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Hindawi Publishing Corporation Advances in Meteorology Volume 2013, Article ID 270192, 9 pages http://dx.doi.org/10.1155/2013/270192 Research Article Numerical Simulation of the Effects of Grassland Degradation on the Surface Climate in Overgrazing Area of Northwest China 1 1 2,3,4 1 3,4 Yanfei Li, Zhaohua Li, Zhihui Li, Xiaoli Geng, and Xiangzheng Deng FacultyofResources andEnvironmental Science, HubeiUniversity, Wuhan, Hubei430062, China University of Chinese Academy of Sciences, Beijing 100049, China Institute of Geographic Science and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China Center for Chinese Agricultural Policy, Chinese Academy of Sciences, Beijing 100101, China Correspondence should be addressed to Xiangzheng Deng; dengxz.ccap@gmail.com Received 17 July 2013; Accepted 26 September 2013 Academic Editor: Burak Guneral ¨ p Copyright © 2013 Yanfei Li et al. 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. The climatic effects of LUCC have been a focus of current researches on global climate change. eTh objective of this study is to investigate climatic eeff cts of grassland degradation in Northwest China. Based on the stimulation of the conversion from grassland to other land use types during the next 30 years, the potential effects of grassland degradation on regional climate in the overgrazing area of NorthwestChinafrom2010to2040havebeenexploredwithWeather Research andForecasting model(WRF).Theanalysis results show that grassland will mainly convert into barren land, croplands, and urban land, which accounts for 42%, 48%, and 10% of the total converted grassland area, respectively. eTh simulation results indicate that the WRF model is appropriate for the simulation of the impact of grassland degradation on climate change. eTh grassland degradation during the next 30 years will result in the decrease of latent heat ux, fl which will further lead to the increase of temperature in summer, with an increment of 0.4–1.2 C, and the decrease of temperature in winter, with a decrement of 0.2 C. In addition, grassland degradation will cause the decrease of precipitation in both summer and winter, with a decrement of 4–20 mm. 1. Introduction and so forth, [7, 8]. eTh refore, it is of great signicfi ance to study the eeff cts of LUCC on regional climate for adapting The influence of human activities on the climate system to climate change. has become the focus of the academic community at home Grasslandasone of themostwidespreadlanduse type andabroadinthe context of global warmingsince the20th covers about 40% of the total land area of China [9, 10]. century [1]. The fourth assessment report of Intergovern- eTh grasslands provide various ecosystem services such as mental Panel on Climate Change (IPCC AR4) indicated that the provision of the forage, milk, and meat. Besides, the the human activities are an important influencing factor of grasslands also providesomeimportant ecosystemservices climate change, accounting for 90% of global warming [2, that regulate the regional climate, for example, the mitigation 3]. Some previous researches have showed that the human- of greenhouse gas (GHG) emissions through soil organic induced land use/land cover change (LUCC) was one of carbon (C) and nitrogen (N) sequestration [11, 12]. eTh refore, the major factors, which inu fl ence the regional climate [ 4]. the grassland change would be the import factor influencing The LUCC influences the climate change mainly through theclimatechange.TheovergrazingareasinNorthwestChina changing the underlying surface properties such as the are the most significant hinterlands. The grassland degra- surface reflectivity, roughness, soil moisture, leaf area, and dation and desertification in overgrazing area of Northwest vegetation coverage [5, 6]. eTh eeff cts of LUCC on the bio- China has greatly intensified due to the irrational exploitation geophysical processes vary from region to region, which are of the natural resources, rapid population growth, and the closely related with the land-atmosphere interaction, regional expansion of road network in recent years [13, 14]. The mean surface climate, environmental background and vegetation, rate of grassland degradation has accelerated overall in the 2 Advances in Meteorology ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 70 E 80 E 90 E 100 E 110 E 120 E 130 E 140 E 105 E 108 E 111 E 114 E Heilongjiang Jilin Inner Mongolia Xinjiang Liaoning Gansu Beijing Tianjin Hebei Shanxi Ningxia Shandong Qinghai Shaanxi Henan Jiangsu Tibet AnhuiShanghai Hubei Sichuan Chongqing Zhejiang Hunan Jiangxi Guizhou Fujian Taiwan Yunnan Guangxi Guangdong (km) Hainan 0 1,050 2,100 ∘ ∘ ∘ 105 E 108 E 111 E Cultivated land Water area ∘ ∘ ∘ ∘ Built-up area Forestry area 90 E 100 E 110 E 120 E Grassland Unused aera Figure 1: Location of the study area and the distribution of land use type in the overgrazing areas of Northwest China. past 50 years and only decelerated in recent years. Moreover, advances of RCMs and is specifically designed for high the grassland degradation has led to the decline of grassland resolution applications and provides an ideal tool for assess- productivity and increased the frequency of extreme climate ing the value of high resolution regional climate modeling, events such as droughts and er fi ce freeze-up, which have and some researchers have identified the WRF model to seriously inu fl enced the sustainable development of animal be superior to other RCMs such as RegCM2, RegCM3, husbandry [14]. eTh refore, it is of great importance to study RAMS, RIEMS, RegCM-NCC, and IPCR-RegCM [1, 25, theinufl enceofgrassland degradation on theclimate in the 26]. overgrazing area of Northwest China. Some studies with the WRF model have shown that eTh re have been many researches focusing on the grassland degradation in overgrazing areas of Northwest impacts of the grassland degradation in overgrazing areas China has obvious eeff ct on the regional climate [ 19, 24]. in Northwest China on climate change. Most of those However, those previous researches about the effects of researches detected the interaction between the grassland grassland degradation on the climate change have generally degradation and the climate change by the selection of focusedonthe eeff cts of land change during thehistorical regional climate model (RCMs) or global climate models period with the numerical simulation models, while there (GCMs) and experiment designs [15]. Xue and Fu et al. were few researches on the impacts of predicted future land identified that grassland degradation over the Mongolian usechangeonthe climate. eTh refore,thisstudy aims to and the Inner Mongolian grassland could bring signicfi ant estimate the potential impacts of grassland degradation on influence on surface climate [ 16, 17]. Zhang et al., found climate change in overgrazing area of Northwest China from that the grassland degradation could lead to the decrease 2010 to 2040 with the WRF model. of precipitation and the increase of surface temperature in Northwest China [18]. Liu et al. found that the grass- land desertification can lead to grand temperature increase 2. Data and Methodology in thedaytime anddecreaseatnight,and thesensitive 2.1. Study Area. The overgrazing area of Northwest China heat u fl x increase and the latent heat ux fl decrease in the ∘ 󸀠 ∘ 󸀠 ∘ 󸀠 ∘ 󸀠 is located in 104 04∼114 02 E, 32 40∼41 20 Nwithatotal Source Regions of Three Rivers [ 19]. All of these previous land area of 811856 km covering five provinces which include researches with GCMs and RCMs have contributed to the Ningxia Province, the south east part of Gansu Province, comprehensive understanding of the impacts of grassland Shaanxi Province, the west part of Shanxi Province, and the change on the climate change at the regional and global middle and south west part of Inner Mongolia Autonomous scales. However, because of the coarse resolution, there Region (Figure 1). It is one of the largest grazing areas of are some bias and uncertainties in the simulation of the regional climatechangewithGCMs[20–24]. The weather China, which is the major production base of the animal Research and Forecasting (WRF) model represents the recent husbandry industry in China. ∘ ∘ ∘ ∘ ∘ 10 N 20 N 30 N 40 N 50 N ∘ ∘ ∘ ∘ 20 N 30 N 40 N 50 N ∘ ∘ ∘ 33 N 36 N 39 N ∘ ∘ ∘ 33 N 36 N 39 N Advances in Meteorology 3 This region stretches across the eastern monsoon region Table 1: Parameterization scheme of physical processes in the WRF model. and northwest arid region and is close to the Qinghai- Tibet alpine region, approximately located in the transition Classification of schemes Scheme option zone of the three major natural zones of China. It is the Physics parameterization scheme WSM3-class simple ice continental semiarid climate in this region, with an annual Cumulus parameterization scheme Grell-Devenyi ensemble average temperature of 5–10 C and the annual precipitation Boundary layer process scheme YSU of 200–800 mm. There is very limited water resource, the Radiation scheme CAM 3 radiation spatiotemporal distribution of which is very imbalanced, and Land surface process scheme Noah land surface model there are frequently meteorological disasters. The grassland and cultivated land are the dominant land use types in this region, accounting for 36.19% and 29% of the total area, respectively. The irrational utilization of 2.3. Description of the WRF Model. The WRF model is grassland resources is very common due to overgrazing and a next-generation forecast model developed by the scien- overreclamation under the inu fl ence of pursuit of economic ticfi research center, atmospheric administration (NOAA), benefit since the 1980s. It has led to the continual degradation research institutions and universities in the United States. of the grassland. eTh proportion of grassland accounting Two motive power cores were included in the WRF model, forthe totalareaofNorthwest Chinahas decreasedfrom that is, ARW (Advanced Research WRF) developed by NCAR about36% in 1995 to 31%in2008, andmostofgrassland and used in scienticfi research and nonhydrostatic Mesoscale degradedintobarrenlandand croplands. eTh intensive Model (MMM) developed by NCEP and widely used in the grassland degradation has resulted in more and more acute business system. This study has mainly used the ARW model contradiction between the human and nature, economic [28]. development and eco-environmental conservation in region. The parameterization scheme of physical processes in Therefore, the exploration of the degree and mechanism of the WRF model in this study is as follows (Table 1). It grassland degradation’s influence on regional climate and mainly includes the WSM3-Class simple ice physical scheme, environment is of great significance to the policy making of ensemble cumulus convection schemes of Grell-Devenyi the regional sustainable land use and management. ensemble, YSU, CAM3 radiation schemes, and consolidated NOAH land surface parameterization scheme [29, 30]. 2.2. Data Resource. In this study, the 1 km resolution land 2.4. Test Design. In this study, two numerical simulation cover data of United States Geological Survey (USGS) clas- tests, including the control test and sensitivity test, were sification in 2010 were extracted from the MODIS dataset. designed and performed with the same horizontal resolu- The land conversion data with 1 km resolution used to tion and parameterization scheme in order to analyze the forecast the information of land use change (land conversion effects of grassland degradation on the regional climate more among different land cover types) during 2010–2040 were accurately, unlike other previous experiment studies in which simulated based on Representative Concentration Pathways the entire grassland was replaced by other land covers. eTh 6.0 (RCP6.0) using the Asia-Pacific Integrated Model (AIM) control test as a reference case used the land cover data of developed by the National Institute of Environmental Stud- 2010, while the sensitivity test used the land cover data from ies (NIES) in Japan. According to the requirement of the 2010 to 2040, in which part of grassland converted into bare WRF model, it is necessary to convert the 1 km resolu- land, croplands, and urban land. The climate forcing data tion land cover data of United States Geological Survey in both the control test and sensitivity test were all from (USGS) classification in 2010 into the 30 km resolution 2010 to 2040. eTh center of the simulated area is located data. ∘ 󸀠 ∘ 󸀠 ∘ at 37 53 N, 109 1 E with two standard parallels of 39 Nand The meteorological data used in this study, including 35 N, including 27 grid points in the east-west direction and the near-surface temperature and precipitation, were all 48 grid points in the north-south direction. The simulation from 84 meteorological stations in Ningxia Province, Inner period is 30 years from January 1st, 2010, to December 31th, Mongolia Autonomous Region, Gansu Province, Shanxi Province, and Shaanxi Province. In order to analyze the simulation accuracy of the WRF model, the original data of annual average temperature, monthly average temperature 3. Result and annual precipitation in year 2010 were interpolated into 1 km resolution grid data with the Kriging interpo- 3.1. Forecast of Future Grassland Degradation in Overgrazing lation method and then compared with the simulation Areas of Northwest China during 2010–2040. The grassland results. in the study mainly concentrates in the south and middle The atmospheric forcing data such as air temperature, part of Inner Mongolia and Ningxia Province, the northeast specific humidity, sea level pressure, eastward wind, north- of Gansu Province, and south part of Shaanxi Province, ward wind, and geopotential height from 2010 to 2040 accounting forabout 35%ofthe totalareaofovergrazing used in this study were from a state-of-the-art multimodel areas in Northwest China. This study stimulates the grassland dataset produced by the h phase of the Coupled Model change of overgrazing areas in Northwest China from 2010 Intercomparison Project (CMIP5) [27]. to 2040. eTh stimulation result indicated that with the fift 4 Advances in Meteorology ∘ ∘ ∘ ∘ ∘ change in the overgrazing areas of Northwest China since the 106 E 108 E 110 E 112 E 114 E performance of the WRF model in different regions may vary greatly. In this study, the simulation ability of WRF model was 40 N tested through comparing the stimulated temperature and 40 N precipitation with the observation data. eTh result indicates that the WRF model can simulate the temporal change of temperature very well (Figures 3(a) 38 N and 4(a)). According to the monthly temperature change in 38 N theentirestudy area,the simulatedtemperature is roughly consistent with the observed value in the spring and winter, ∘ ∘ and the difference between them ranges from 0 Cto0.5 C 36 N ∘ (Figure 3(a)). However, the temperature is obviously lower 36 N than the observed value in both the summer and autumn, with the dieff rence between them ranging from 0.5 Cto 2.5 C. As canbeseenfromFigure 4(a),the stimulated annual 34 N average temperature is lower than the observed value, and 34 N ∘ ∘ the difference between them ranges from 0.2 Cto1.4 C, indicating that there is only slight difference between the stimulated and observed annual average temperature. ∘ ∘ ∘ ∘ 106 E 108 E 110 E 112 E As canbeseenfromFigure 3(b), the stimulated precip- itationinthe spring andautumnof2010islower than the Barren or sparsely vegetated land observed value, and the difference between them ranges from Urban and built-up land 5mmto40mminmostmonthsexceptJune. Figure 4(b) Dryland cropland and pasture reveals that the annual precipitation of 2010 in overgrazing Grassland Others areas in Northwest China, especially the southeast part of Grassland converts to barren or sparsely vegetated land Gansu Province and northwest of Shaanxi Province, is lower Grassland converts to dryland cropland and pasture than the observed value, and the dieff rence between them Grassland converts to urban and built-up land generally ranges from 5 mm to 30 mm. In summary, the difference between the simulated and observed monthly and Figure 2: Conversion from grassland to other land use types annual change of precipitation is not very obvious. eTh refore, between 2010 and 2040 of the overgrazing areas in Northwest China. the WRF model can well simulate the monthly and annual change of precipitation very well. increasing population and unreasonable use of the grassland, 3.3. Eeff cts of Grassland Degradation on Latent Heat Flux. The the grassland degradation is still severe, in the future 30 years; land cover change can influence the energy balance of the the conclusion will be coherent with that of previous study earth-gas system through changing the underlying surface [31]. There will be mainly the conversion between grassland parameters such as the land surface albedo, roughness, and and croplands, bare land, and urban land. soil water content [26]. Latent heat u fl x is the indispens- This study also statistically analyzed the number of grid able element of energy exchange between land surface and cells converting from grassland into other land types between atmosphere [32]. The grassland degradation could decrease 2010 and 2040. The result indicates that there will be 55 the roughness, which would lead to the decrease of latent grids converting from grassland into other land types from heat exchange in the earth-gas system. As can be seen from 2010 to 2040 in the study area (Figure 2). About 48% of Figure 5, the grassland degradation would result in the the converted grassland will convert into croplands, which obvious decrease of the average monthly latent heat u fl x from mainly distributed in the southeast part of Inner Mongolia March to July, and the maximum decrement reaches about Autonomous Region, northwest part of Shaanxi Province, 10 W/m . and northeast part of Gansu Province. eTh obvious con- version from grassland into barren land will mainly occur in south and central part of Inner Mongolia and Shanxi 3.4. Effects of Grassland Degradation on the Land Surface Tem- Province, south part of Ningxia Province, and southeast part perature. The land use/cover change influences the regional of Gansu Province, accounting for 42% of the total number surface temperature through altering the land roughness, and of converted grids. er Th e will be 9 grids converting from soil hydrological and thermal features, which lead to further grassland into urban land, accounting for about 10% of the change of the land surface energy balance, long wave radia- total number of converted grids. In summary, the grassland tion, ux fl es of momentum, sensible heat and latent heat, and in overgrazing areas in Northwest China will mainly convert so forth [33]. While the impacts of grassland degradation on into barren land and croplands. the temperature in overgrazing areas of Northwest China can be analyzed through calculating the dieff rence in the annual 3.2. Result of the Control Test. It is necessary to investigate average near-surface temperature (air temperatures at two whether the WRF model can well simulate the climate meters above the ground) between the results of the control Advances in Meteorology 5 30 2.5 1400 50 25 45 1.5 0.5 123456789 10 11 12 −5 −10 −0.5 0 0 123456789 10 11 12 Observed Observed Simulated Simulated Observed-simulated Observed-simulated (a) (b) Figure 3: Difference between the observed and simulated monthly temperature ((a), unit: C) and precipitation ((b), unit: mm) of 2010 in the overgrazing areas of Northwest China. ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 106 E 108 E 110 E 112 E 106 E 108 E 110 E 112 E Inner Mongolia Inner Mongolia Shanxi Shanxi Ningxia Ningxia Shaanxi Shaanxi Gansu Gansu Henan Henan Hubei Hubei Sichuan Sichuan ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 106 E 108 E 110 E 112 E 106 E 108 E 110 E 112 E <− 30 −20–15 < − 1.4 −1.0–0.6 −1.4–1.0 > − 0.2 −30–25 −15–10 −25–20 >− 5 (a) (b) Figure 4: Difference between the simulated and observed annual average temperature ((a), unit: C) and annual precipitation ((b), unit: mm) in the overgrazing areas of Northwest China in 2010. test and sensitivity test on the basis of the simulation in the winter in the middle part of Inner Mongolia Autonomous control test and sensitivity test, the simulation result indicates Region, southwest of Ningxia Province, and northwest of that there will be different climate effects of the grassland Shanxi Province due to the conversion from grassland to degradation in different areas and seasons from 2010 to 2040 barren land and urban land with the decrement reaching in the overgrazing areas of Northwest China (Figure 6). 0.2 C(Figure 6(a)). Although the near-surface temperature Besides, the results of the two tests showed that the grassland of the winter increased in the middle part of Shaanxi Province degradation wouldincreasethe land surfacealbedo, which and north part of Shanxi Province due to the decrease of could lead to the decrease of near-surface temperature in the land surfacealbedocausedbyconversionfromgrassland to Observed/stimulated value ( C) ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N ∘ ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N Observed-stimulated value ( C) ∘ ∘ ∘ ∘ Observed/stimulated value (mm) 34 N 36 N 38 N 40 N ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N Observed-stimulated value (mm) 6 Advances in Meteorology 123456789 10 11 12 Control experiment Sensitive experiment Figure 5: Average monthly change of latent heat flux (unit: W/m ) in the overgrazing area of Northwest China from 2010 to 2040. ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 106 E 108 E 110 E 112 E 106 E 108 E 110 E 112 E Inner Mongolia Inner Mongolia Shanxi Shanxi Ningxia Ningxia Shaanxi Shaanxi Gansu Gansu Henan Henan Hubei Hubei Sichuan Sichuan ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 106 E 108 E 110 E 112 E 106 E 108 E 110 E 112 E < − 0.2 < − 0.4 0.8–1.2 0.4–0.6 −0.2–0 0–0.4 >1.2 >0.6 0.2–0.4 0.4–0.8 (a) (b) Figure 6: Difference in the annual average temperature (unit: C) in the winter (a) and summer (b) from 2010 to 2040 in the overgrazing areas in Northwest China between the sensitivity test and the control test. croplands, the grassland degradation can mainly result in and middle part of Shaanxi, which are in the overgrazing the decrease of the near-surface temperature of winter in the areas of Northwest China, with the increment of about study area. 1.2 C. The impacts of grassland degradation on the near- Although surface temperature of summer decrease in the surface temperature are more complicated and widespread southpartofInner Mongolia,the southpartofShaanxi in the summer than that in the winter. eTh grassland Province, and south east of Gansu Province with the drop degradation candecreasethe surfacealbedo, whichwill scale of about 0.4 C(Figure 6(b)), which would be caused result in the increase of the near-surface temperature in by the conversion from grassland to croplands since there is the overgrazing areas of Northwest China, with an incre- obvious difference between the surface albedo of croplands ∘ ∘ ment of about 0.4 C–1.2 C(Figure 6(b)). The temperature and grassland and the higher evapotranspiration of the crop- rise most obviously in the southwest of Inner Mongolia lands, the grassland degradation would mainly lead to the ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N Latent heat flux (W/m ) ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N Advances in Meteorology 7 ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 106 E 108 E 110 E 112 E 106 E 108 E 110 E 112 E Inner Mongolia Inner Mongolia Shanxi Shanxi Ningxia Ningxia Shaanxi Shaanxi Gansu Gansu Henan Henan Hubei Hubei Sichuan Sichuan ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 106 E 108 E 110 E 112 E 106 E 108 E 110 E 112 E <− 12 4–8 <− 20 −12–8 >8 >− 4 0–4 −20–16 −16–12 (a) (b) Figure 7: Difference in the annual precipitation (unit: mm) in the winter (a) and summer (b) from 2010 to 2040 in overgrazing areas of Northwest China between the sensitivity test and control test. increase of surface temperature of summer in the overgrazing China will make the climate change show a dry-warm trend areas of Northwest China. according to the results of both the control test and sensitivity test. eTh results are consistent with theoretical analysis results that the vegetation degradation will cause the increase of 3.5. eTh Eeff ctofGrassland DegradationonPrecipitation. The surfacealbedo, surfacesensibleheat, andthe decrease of land cover change can influence the precipitation through latent heat and thereby lead to the decrease of precipitation modifying both the energy balance and water balance [26, and increase of temperature [34]. 33]. There are very complex impacts of grassland degradation on the precipitation. Due to the complicated interactions between land surface and atmosphere, such as the inter- 4. Conclusion and Discussion actions between land surface albedo, soil moisture, sand temperature, the grassland degradation will increase surface Basedonthe analysis of grasslandchangeinthe future,this albedo, reduce roughness, and weaken the regulation func- study analyzed the impacts of grassland degradation on the tion of vegetation cover in the water cycle [26]. regional climate in the overgrazing areas of Northwest China The simulation result indicates that the grassland degra- through implementing the numerical simulation with the dation can cause the decrease of precipitation in the winter WRF model. eTh conclusions of this study are as follows. in most part of the overgrazing areas of Northwest China, eTh resultindicatesthattheWRFmodelcanwellsimulate with a decrement from about 0 mm to 12 mm (Figure 7(a)). the spatial pattern and change of temperature and precipi- Particularly, the annual precipitation in the northwest part tation, although the simulated value is a bit lower than the of Shanxi Province and south part of Inner Mongolia observed value. Besides, the grassland of Northwest China Autonomous Region will decline most obviously due to would mainly degrade into croplands, bare land, and urban the serious grassland desertification, with a decrement of land over the next 30 years. The most obvious grassland about 12 mm. Besides, in the summer, the conversion from change will occur in the central part of Inner Mongolia grassland to barren land can result in the obvious decrease Autonomous Region and northwest part of Shaanxi Province. of precipitation in north and central part of Shanxi Province, The simulation result indicates that the grassland degra- north part of Inner Mongolia, and Ningxia Province, with the dation will make the climate change in the overgrazing areas decrement ranging from about 4 mm to 20 mm (Figure 7(b)). of Northwest China show a dry-warm trend in the future The abovementioned numerical simulation of tempera- 30 years. The grassland degradation will lead to the decrease ture and precipitation in the next 30 years shows that the of latent heat flux through influencing the phase change of grassland degradation in the overgrazing areas of Northwest water in the atmosphere and the surface-airheatexchange. ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N ∘ ∘ ∘ ∘ 34 N 36 N 38 N 40 N 8 Advances in Meteorology The impacts of grassland degradation on the climate will [8] J.Jin andL.Wen,“Evaluation of snowmelt simulation in the weather research and forecasting model,” Journal of Geophysical vary in dieff rent seasons. In the summer, the grassland Research,vol.117,2012. degradation will lead to the increase of surface temperature [9] T. Akiyama and K. Kawamura, “Grassland degradation in and decrease of precipitation. 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In addition, there are various factors that grasslands of China based on field measurements of above- and influence the regional climate, but in this paper, only the below-ground biomass,” Climatic Change,vol.86, no.3-4,pp. land cover change is used to analyze the impacts of grassland 375–396, 2008. degradation on the regional climate, which leads to some [12] F. Barthold,M.Wiesmeier,L.Breuer, H. Frede, J. Wua, andF. uncertainties of the results. eTh refore, more efforts should be Blank, “Land use and climate control the spatial distribution of made in the future research on the sensitivity test to reduce soil types in the grasslands of Inner Mongolia,” Journal of Arid the uncertainties of the results. Environments, vol. 88, pp. 194–205, 2012. [13] G. Xu, M. Kang, and Y. 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