Effects of Summer Rainfall on the Soil Thermal Properties and Surface Energy Balances in the Badain Jaran Desert
Effects of Summer Rainfall on the Soil Thermal Properties and Surface Energy Balances in the...
Li, Jiangang;Mamtimin, Ali;Li, Zhaoguo;Jiang, Cailian;Wang, Minzhong
2019-12-06 00:00:00
Hindawi Advances in Meteorology Volume 2019, Article ID 4960624, 13 pages https://doi.org/10.1155/2019/4960624 Research Article Effects of Summer Rainfall on the Soil Thermal Properties and Surface Energy Balances in the Badain Jaran Desert 1,2 1,2 3 4 1,2 JiangangLi , AliMamtimin , ZhaoguoLi, CailianJiang, andMinzhongWang Institute of Desert and Meteorology, CMA, Urumqi 830002, China Center of Central Asian Atmospheric Science Research, Urumqi 830002, China Key Laboratory of Land Surface Process and Climate Change in Cold and Arid Regions, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China Wujiaqu Meteorology Bureau, Wujiaqu 831300, China Correspondence should be addressed to Ali Mamtimin; ali@idm.cn Received 20 April 2019; Revised 11 October 2019; Accepted 13 November 2019; Published 6 December 2019 Academic Editor: Stefano Dietrich Copyright © 2019 Jiangang Li et al. *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. Based on observational data collected during the summer of 2009 from the southern Badain Jaran Desert, the surface sensible and latent heat fluxes and shallow soil thermal storage were obtained through corrections and quality control measures. *e soil thermal properties and characteristics of the land surface energy budget before and after rainfall episodes were systematically analyzed. Short- term precipitation had a greater influence than systematic precipitation on the soil temperature (ST) and soil volumetric water content (VWC). After rainfall, the VWC rapidly increased, showing a decreasing growth rate trend with depth and time in all layers; the soil temperature change rate (TCR) exhibited the opposite tendency. *e surface albedo, which was affected little by the solar elevation angle and short-term precipitation, fluctuated from low to high during short-term rainfall. *e soil thermal parameters, including the volumetric heat capacity, thermal conductivity, and diffusivity, all increased after rainfall. *e diurnal soil heat flux variations in each layer manifested as quasisinusoids, and the amplitude gradually decreased with depth. *e energy balance ratio (EBR) without and with soil heat storage (S) varied differently; after incorporating S, the EBR increased by approximately 5-6% regardless of rainfall but remained lower afterward. *roughout the observation period, the maximum daytime EBR appeared approximately 1-2 days before or after rainfall and gradually declined otherwise. *ese findings are fundamental for understanding the influences of cloud and precipitation disturbances on radiation budgets and energy distributions and improving the param- eterization of surface radiation budgets and energy balances for numerical models of semiarid areas. While partitioning of land surface fluxes, the soil has a 1.Introduction larger role to play on the hydrological cycle as they are tightly Global warming not only leads to an increase in air tem- connected with both land-atmosphere energy and water perature but also changes the amount, intensity, and fre- exchanges [4, 5]. Previous studies have shown that soil has a quency of precipitation [1]. Since the 20th century, the profound impact on the atmospheric surface layer, and the precipitation falling over the mid-high latitudes of the distribution and characteristic parameters of soil have Northern Hemisphere has increased by approximately 7– certain effects on land-atmosphere energy exchange, water 12%, but the spatial distribution of this precipitation is exchange, and the hydrological cycle [6–8]. *e transport of uneven and exhibits a high degree of heterogeneity, which both soil heat and water from the land surface to deeper results in both an increased degree of uncertainty regarding layers is closely related to soil structure parameters, such as the occurrence and duration of extreme precipitation and an the soil composition, volume-weight ratio, humidity, and enlargement of drought areas. *e latter phenomenon in- soil thermal parameters, including the soil thermal con- tensifies hydrologic processes in terrestrial ecosystems, ductivity, thermal capacity, thermal diffusivity, and specific particularly in arid and semiarid areas [2, 3]. heat [9]. Accordingly, some researchers have studied the 2 Advances in Meteorology thermal properties and heat fluxes of soil using a variety of area of approximately 52,000 square kilometers [32]. *is methods and products [10–15], including the NOAH Land desert is mainly influenced by westerlies, namely, the Indian Surface Model (LSM) for estimating net radiation and latent, and East Asian monsoons, and belongs to temperate arid sensible, and ground heat (GH) fluxes as well as water and extremely arid climate zones. *e average annual balance components in four land treatments [16], a hy- precipitation exhibits a decreasing trend from the southeast drological model for the simulation of soil moisture across (approximately 120 mm) to the northwest (less than 40 mm) multiple depths [17]. [33]; precipitation primarily occurs from July to August. *e *e majority of arid regions in Northwest China are northwest arid area, which is subject to a large amount of desert or Gobi and are subject to intense solar radiation; as a evaporation and abundant sunshine, is sensitive to climate result, the soil parameters are vastly different from those of change and possesses a fragile ecological environment. typical regions, and the land surface physical processes Hence, the northwest arid area is considered an ideal site to therein exhibit notable regional characteristics [18]. Since observe the water and heat exchanges in the underlying the late 1980s, comprehensive field experiments have been desert surface. carried out on land surface processes. *e Heihe River field From June to September of 2009, researchers carried out experiment (HEIFE) and the field experiment on the air- a series of field observation experiments in the hinterland of land interaction in the arid area of Northwest China (NWC- the Badain Jaran Desert. *e observation points were located ° ° ALIEX) have confirmed certain soil parameters in the soil in the southeast of the desert (39 28.122′N and 102 22.365′E surface of their research regions [19–22]. However, com- at an altitude of 1418 m). *e D1 observation site, which was paratively speaking, specific research on the soil parameters surrounded by an open, undulating yellow sand terrain, is a in arid regions is still limited. characteristic desert area. Sparse vegetation was distributed As the main water source in desert areas, precipitation approximately 500∼700 m from the observational station, has a considerable impact on the movement of dunes and the most of which was Alhagi sparsifolia, and Nitraria tangu- distribution of vegetation [23–27]. Due to limitations posed torum Bobr was also present (as shown in Figure 1). by the natural environment, only a small number of ob- *e air temperature and humidity, wind, precipitation, servation stations with an uneven spatial distribution are soil temperature (ST, hereinafter) and soil moisture (volu- situated in the arid desert area of Northwest China; as a metric water content, VWC hereinafter), land surface ra- result, the characteristics of the soil physical parameters diation, and turbulence were observed. *e IOP lasted from therein, specifically in the untraversed desert hinterlands, are June 21st to September 12th. In this paper, the local standard poorly understood. Nevertheless, local meteorologists have time (LST, hereinafter), which was 7 h ahead of Coordinated conducted a large amount of research in the Taklamakan and Universal Time (UTC), was selected for the calculation and Gurbantunggut Deserts, and their work has resulted in analysis. numerous achievements with regard to the effects of pre- *e data from August 4th to September 20th were se- cipitation on deserts and their surrounding areas [28–30]. lected for analysis to reflect the effects of rainfall on the soil *e Badain Jaran Desert is host to a variety of wavy thermal properties and energy balances in the desert hin- landforms and sand mountains, the latter of which are the terland. During this period, there were two large-scale highest in the world, and these landforms have profound precipitation events: one occurred on August 18th with effects on rainfall. Zhang et al. analyzed the rainfall distri- 29 mm of precipitation and the other occurred on September bution in this region based on data from meteorological 5–7th with 22.6 mm of total precipitation. *ese events stations located around the desert [31]. However, few studies represent rare phenomena in this extremely arid desert area. have investigated the effects of rainfall on the thermal properties of soil in deserts. In this paper, hourly rainfall data acquired during the 2.2. Methods. *e hourly precipitation distributions of the two aforementioned synoptic processes are shown in Fig- intense observation period (IOP, hereinafter) in the Badain Jaran Desert hinterland were integrated. Basic data, in- ure 2, which shows that the first weather event (August 18th) had a short precipitation duration with a high intensity; the cluding the surface sensible heat flux, latent heat flux, and − 1 shallow soil thermal storage data, were obtained, and the maximum rainfall intensity reached 7.8 mm·h . In contrast, surface albedo, soil volumetric heat capacity, thermal con- the second weather event had a longer duration, but the − 1 ductivity, thermal diffusivity, and energy balance ratio (EBR) maximum intensity was only 2.8 mm·h . *is result in- were calculated by relevant equations. *e effects of different dicates that the two precipitation processes were notably types of rainfall on these soil characteristics and on the different; the first weather event was an extremely intense surface energy balances were analyzed, the results of which rainfall episode, the sort of which is typical in the arid region of Northwest China, while the second weather event was reveal the energy and water distributions in the underlying surface layer throughout the arid region of Northwest China. characteristic of systematic rainfall. *e sampling frequency of the surface turbulence data was 10 Hz, while the radiometer and soil heat flux plate 2.Materials and Methods generated average ST and VWC values, respectively, every 2.1. Materials. *e Badain Jaran Desert, located in the Alxa 30 min. Basic data quality control measures, such as outlier ° ° elimination, time delay correction, virtual temperature cor- Banner of Inner Mongolia at approximately 39.5 –42 N and ° ° 98.5 –104 E, is the second-largest desert in China with an rection, and Webb–Pearman–Leuning (WPL) correction, Advances in Meteorology 3 Inner Gansu Mongolia 42°N Ejina Qi Ningxia Qinghai Guaizi lake 41°N Dingxin Bayinnuorigong 40°N Jinta D1 Gaotai Alxa Right Banner 39°N Zhangye 0 35 70 140 210 Km 99°E 100°E 101°E 102°E 103°E 104°E 105°E Weather station Observation station Desert region Figure 1: Observation site and surface conditions in the Badain Jaran Desert. 9.0 3.0 8.0 7.0 6.0 2.0 5.0 4.0 3.0 1.0 2.0 1.0 0.0 0.0 00:00 02:00 04:00 06:00 08:00 10:00 00:00 08:00 16:00 00:00 08:00 16:00 00:00 (Aug 18) (Sep 5) (Sep 6) (Sep 7) Time/LST Time/LST (a) (b) Figure 2: Hourly precipitation distributions of the two weather events: (a) August 18th; (b) September 5–7th. were applied. To enhance the comparability, only data that statistics of the turbulent quantities of the wind temperature had been averaged over 0.5 h intervals and controlled for and humidity, respectively. quality were used for analysis in this paper. *e water-bearing soil volumetric heat capacity C , *e surface sensible heat flux (H) and latent heat flux water-free soil volumetric heat capacity C , thermal con- sd (LE) were calculated by the eddy covariance method [34]: ductivity λ , and thermal diffusivity K were calculated si si according to the following formulas [35]: ′ ′ (1) H � ρ∗ C ∗ w θ , G − G 1 2 c � , (3) Δz∗ zT /zt ′ ′ (2) g LE � ρ∗ λ∗ w q . In formulas (1) and (2), ρ is the air density, C is the P G − G − V ∗ C ∗Δz∗ zT /zt 1 2 w w g c � , (4) specific heat at a constant pressure, and λ is the latent heat of sd Δz∗ zT /zt ′ ′ ′ ′ evaporation; the latter two are constants. w θ and w q are Precipitation (mm) Precipitation (mm) 4 Advances in Meteorology episode than before the second episode. With the infiltration λ � , (5) si of rainwater, the VWC increased rapidly, and the VWC zT /zz increase from shallow to deep layers exhibiting a declining trend, similar to the result of research in the Nebraska si Sandhills [27]. Based on the change in the VWC in each layer K � . (6) si with time, the VWC was delayed 1.5 h at depths of ap- proximately 5–20 cm and 4 h at depths of 20 and 40 cm. In formula (3), G and G are the two observed soil heat 1 2 After each rainfall episode, the VWC tended to decrease, and flux values in the upper (5 cm) and lower (20 cm) layers, the lapse rate at depths of approximately 5–20 cm was larger respectively,Δz is the thickness between the two observation than that at a depth of 40 cm and decreased with time. layers, and zT /zt represents the average ST change rate During the second rainfall episode, as the rainfall intensity between the observation depths of the soil heat flux in the was relatively small, the growth rate of the VWC was less two layers. In formula (4), V is the soil volumetric water notable than that during the first rainfall episode. *e lag content and C is the specific heat of water, which is time of the VWC change in each layer was notably pro- 4.2∗10 J/(kg· C). In formula (5), G is the heat flux of the longed with a 6 h delay at depths between 20 and 40 cm. desired soil depth and zT /zz represents the vertical ST Figure 3(b) shows the variations in the soil temperature gradient. change rate (TCR, hereafter) before and after the first rainfall Since it was difficult to directly measure the surface heat episode in various layers. Evidently, the TCR at a depth of flux, in this paper, the thermal storage in the shallow soil 5 cm before rainfall was in the range of − 3 to 4 C with a layer was calculated with the thermal diffusion equation and distinct diurnal variation cycle, while the variability in other correction (TDEC) method [36]. *at is, the surface heat layers decreased with increasing depth. *is phenomenon flux was derived by using the measured 5 cm soil layer heat indicates that the soil was dry, possessed a suitable heat flux and the soil thermal storage of the above 5 cm layer as transfer capacity, and was easily influenced by solar radia- follows: tion in the shallow layer. After rainfall, the TCR notably G � G + S, (7) sfc z increased and was negative at depths of approximately 5– 10 cm, indicating that the short-term precipitation caused a z�z ref zT rapid decrease in the ST while having little effect on the S � ρ ∗ C ∗ dz. (8) s s zt deeper soil layers. During the second rainfall episode, the z�0 TCR was similar to that during the first rainfall episode, but In formula (7), G and S represent the soil heat flux and its variation was clearly smaller with a longer duration. thermal storage of the 5 cm layer, respectively. In formula However, in the deeper layers, the TCR increased to larger 3 − 3 (8), ρ is the soil density, which is 1.6∗10 kg·m [37]; C is s s values than those during the first rainfall episode; this the soil specific heat; z is the reference depth, which is ref discrepancy was related to the slow, long-term infiltration of 0.05 m; and zT/zt represents the temperature change rate rainwater. between the surface and reference depth. To compare the diurnal variation trends of the TCR *e following calculation formulas were employed for between the soil and air, the mean diurnal air TCR and the surface net radiation R , albedo α, and EBR: corresponding soil TCR were calculated on rainy and clear R � R + R − R − R , (9) days for the entire period, as shown in Figure 4. As rainfall n SD LD SU LU fell, the air TCR changed quickly, while the soil TCR R gradually decreased and was lagged by approximately 1 h SU α � , (10) successively at depths from 5 cm to 20 cm; however, the TCR SD at a depth of 40 cm changed very little and was lagged by approximately 5 h behind that at a depth of 20 cm (H + LE) EBR � . (11) (Figure 4(a)). Figure 4(b) shows the same diurnal trends, but