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The spatial distribution of groundwater exploitation potential is crucial to the sustainable management of groundwater resources in arid regions. In this study, an effective approach is developed using a geographical information system (GIS) associated with the Dempster-Shafer (D-S) theory to explore the groundwater exploitation potential based on eight factors (i.e., slope, topography, distance to a river, canal density, lithology, land use, soil type, and groundwater depth)based on pumping test data. Different groundwater exploitation potential zones from the output map are classified as follows: very high (0.67–0.96, 8% of the total area), high (0.45–0.67, 8%), moderate (0.27–0.45, 14%), low (0.13–0.27, 24%), and very low (0.02–0.13, 46%), in the Hotan River basin of the Kunlun Mountains, China. The groundwater exploitation potential is highest in a gravel plain in the piedmont and gradually decreases from the piedmont to the desert. The predicted spatial variability of groundwater exploitation potential can explain 71% of the measured pumping test data. The uncertainty of the groundwater exploitation potential map ranges from

With the progress of urbanization, atmospheric pollution and physical health issues caused by the increase of aerosol optical depth (AOD) become more and more prominent. Hence, population exposure risk to AOD becomes a research hotspot. The arid Central Asia (ACA) has a generally high AOD and is a major source area for dust aerosols in the world. Only few studies have discussed population exposure risk to AOD in ACA. Based on multisource remote sensing data, and used population exposure risk model, this study evaluated population exposure risk to AOD in six ecological zones (Northern steppe region of ACA (NSCA), Aral Sea desert area (ASDA), Tianshan Mountains (TSMT), Junggar Basin desert area (JBDA), Tarim Basin desert area (TBDA) and Hexi corridor desert area (HCDA)). Generally, AOD in ACA was kept increasing from 2000 to 2015, and it increased mostly in HCDA and areas near the Aral Sea (p 0.001). With respect to seasonal variations, the maximum AOD was observed in spring and autumn, and the minimum was in winter. Considering land use changes, AOD was mainly manifested by the reduction of water bodies and expansion of construction lands. This was the mostly significant in NSCA and ASDA (p 0.01). The population exposure risk to AOD in ACA was increasing continuously from 2000 to 2015, and high-value regions (9) concentrated in oases, specifically, in the Aral Sea basin and Tarim River basin.The Aral Sea basin became the major AOD source region in ACA due to the shrinking water area after unreasonable development and utilization of water resources. These further increase population exposure risk to AOD in the Aral Sea area. Hence, ecological restoration in terminal lakes of ACA will become the key to lower population exposure risk to AOD practically.

The quantitative description of relationships and propagation between different forms of drought at multiple spatiotemporal scales in various geographical locations is informative for early drought warning systems. This study intends to evaluate the historical hydrometeorological drought from 1984–2015 in the Soan River Basin, which is a critical water source for the Pothwar region of Pakistan. The reconnaissance drought index (RDI) and standardized runoff index (SRI) are used to characterize meteorological and hydrological droughts, respectively. The spatiotemporal variations of the RDI and SRI demonstrated that 2000 and 2010 were extremely dry and wet years, respectively. The results further reveal that the frequency of hydrometeorological drought events was higher in a shorter time scale (3 and 6 months), while durations featured longer timescales (9 and 12 months). The RDI and SRI time series showed a significant decreasing trend in terms of the Mann–Kendal and Sen slope estimator (SSE) results. Cross-correlation analysis for RDI and SRI with a time lag acknowledged the existence of a sequence between the RDI and SRI and a positive relationship between the two indices. The findings of this study could be helpful for better understanding drought variability and water resource management.

The ecosystem service value (ESV) of wetlands is a major concern in ecological research. However, inland lake wetland ecosystems in arid areas are easily overlooked and seldom quantitatively evaluated due to their relatively low biological production. In this study, the ESVs of the Ebinur Wetland Complex (EWC) in Xinjiang, China, were investigated for 11 land use types based on satellite data collected in 2000, 2005, 2010 and 2015. The results show that the land use/cover change (LUCC) in the EWC has been both naturally and anthropogenically affected since 2010, especially in constructed lands, shoal lands and marsh lands. The ESV of the EWC has increased overall, with a total increase of 6.34 × 108 yuan from 2000 to 2015. The ESVs were quantitatively evaluated according to the Millennium Ecosystem Assessment (MA) under different LUCCs. The ecosystem service factors (food supply (FS), wind prevention and sand fixation (WPSF), soil conservation (SC), and carbon fixation and oxygen supply (CFOS)) exhibited strong correlations (R2 > 0.75) and synergies. The FS value accounted for the largest proportion (38.78%) of the ESV in the EWC, followed by the WPSF value (31.93%) and SC value (19.33%). Among the LUCCs, the ESV arable lands accounts for the largest fraction (49.97%) of the total ESV in the EWC. However, the increase was caused by the significant improvement in provisioning services such as arable lands at the expense of regulating and supporting services such as grassland and forest land (mainly cultivated to arable lands). Therefore, integrated strategies, such as the use of plantation water-saving crops, drip irrigation, captive breeding and the establishment of a nature reserve, will lead to sustainable development of the ESV in the EWC.

Actual evapotranspiration (ETa) is an essential component of Earth's global energy balance and water cycle. The Paris Agreement aspires to limit global mean surface warming to2 °C and no1.5 °C relative to preindustrial levels. However, it is uncertain how this global level will impact the shifts in the extents of sandy areas caused by global desertification. Using Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) datasets and advection-aridity models, we investigated the spatiotemporal features of ETa in sandy areas in northern China under global warming scenarios of 1.5 °C and 2.0 °C. The four climate models indicated significant increases in ETa in arid areas across northwestern China. Over time, the ETa value under only the representative concentration pathway 2.6 (RCP2.6) emission scenario increased towards a plateau and significantly increased in the other three emission scenarios (P 0.01) under global warming of 1.5 °C and 2.0 °C. In terms of the spatial variations, ETa showed an increasing trend in all seasons except winter. The maximum ETa was 84.61 mm, and high values were mainly located in the southeast of the study area. Precipitation and the normalized difference vegetation index (NDVI) showed good correlations with ETa in the sandy areas in northern China. The sandy areas in northern China showed decreasing trends (0.45 km

Riparian plant diversity is sensitive to changes in groundwater in arid regions. However, little is known about how plant diversity responds to changes in environment along riverside-desert gradients in riparian ecosystem. Our objectives were to (i) identify riparian plant diversity along riverside-desert gradients in Tarim desert riparian forests, (ii) analyze the impact of environment variables on plant diversity, (iii) determine the optimum groundwater depth for different plant life-forms. Six transects 90 quadrats (with each size 100 m × 100 m) distributed vertically to river bed along riverside-desert gradients ~30 km in length were surveyed. At each quadrat, the morphological features of riparian plant communities were measured, and the groundwater depth, soil water, soil salinity, soil nutrient were also monitored at same sites. Three distinct vegetation communities were identified based on cover and richness in the tree, shrub and herb layers: the riparian zone, the transitional zone and the desert margin zone. Twelve species were indicators of the three vegetation communities. Riparian plant diversity was influenced by groundwater depth, distance from river, soil moisture content, soil salinity and soil nutrient by redundancy analysis. In response to groundwater depth, the optimal groundwater depths for species diversity, evenness and shrub cover were 2.8, 2.7 and 3.7 m, respectively. Therefore, maintaining high plant diversity requires managers to ensure stable groundwater depth for different plant life-forms rather than for some of them.

Accurate predictions of water vapor at large temporal and spatial scales are particularly important in global studies. In recent years, Central Asian grasslands have been subject to both intensive grazing and variability in climatic conditions. However, uncertainties about grazing on water cycling under climate change still exist. Therefore, the Biome-BGC grazing model was applied to assess the effects of grazing on evapotranspiration (ET) and water use efficiency (WUE). Three grassland types were studied during the period 1979–2011: forest meadow (FM), temperate grassland (TG) and desert grassland (DG). ET shows a gradual decreasing trend from FM (365.65 ± 36.86 mm m−2 yr−1) to DG (183.32 ± 21.15 mm m−2 yr−1), and WUE ranging from 0.62 ± 0.03 g C kg-1 H2O in FM to 1.12 ± 0.10 g C kg−1 H2O in TG, with an average of 0.83 ± 0.05 g C kg−1 H2O. Although there was a significant decrease in ET of 1.47–2.72 mm m−2 yr−1, WUE increased at a rate of 0.004 g C kg−1 H2O yr−1 in Central Asia. From 1979 to 2011, grazing lowered ET by 7.47% in Central Asia; the reduction rates for FM, TG and DG were 3.10%, 12.70% and 7.42%, respectively. In general, grazing decreased WUE by 3.60%. From non-grazed to grazed scenario, WUE increased by 6.86% for FM, but WUE decreased by 7.27% and 5.61% for TG and DG. An over-compensation of GPP under grazing might account for the higher WUE under certain grazing intensities. In order to achieve maximum utilization of water efficiency, proper grazing intensity for TG, DG and FM should be limited to 0.17, 0.39 and 0.38 head/ha, respectively.

The Upper Tarim River basin, contributing about 85% of the total inflow to the mainstream Tarim River, is heavily influenced by climate change and human interferences. This study is the first integrated assessment of agriculture and water management under climate change scenarios for this arid river basin in Central Asia. It aims to analyze changes in river discharge of the Upper Tarim under 28 climate projections for 3 representative concentration pathways (RCP) and the A1B scenario and 30 combinations of changes in land use (agricultural area) and water saving measures considered as adaptation strategies. Headwater discharge simulations of two hydrological models (SWIM-G and WASA) are used to drive a hydrological model of the lowland area (SWIM-oasis), taking account irrigation and river transmission losses. The projections show that the river discharge of the Upper Tarim River is likely to increase in a warmer climate if the agricultural area is reduced to the level as in 1998 even without any water saving measures. If the agricultural area increases to the 2010 level, strong water saving measures must be applied to ensure sufficient water inflow to the mainstream Tarim under all climate scenarios. If agricultural area continues to expand, there is a risk of decreasing river discharge at the end of this century under the RCP2.6 scenario. The uncertainty of the projections is large, especially in the far future, and it is mainly related to the climate and hydrological models.

Ecological restoration of degraded riparian Tugai forests is a key driver to combat desertification in arid regions. Previous studies have focused mainly on changes in groundwater as the underlying mechanisms of Tugai forest’s decline. We evaluated species composition and diversity of Tugai forest and their relationship to groundwater, soil salinity, and soil nutrient. Using 73 quadrats (100 m × 100 m) from 13 transects located perpendicularly to river in the upper reaches of the Tarim River. Eighteen plant species belonging to sixteen genera and eight families were recorded, and the dominant species included Populus euphratica, Phragmites communis, and Tamarix ramosissima. Three P. euphratica stand ages were detected: young stand, mature stand, and old stand. There were significant differences in species diversity, groundwater depth, groundwater salinity, distance from the quadrat to the river channel, soil moisture content, pH, electrical conductivity, total salt, Cl−, SO42−, Ca2−, Mg2+, Na+, K+, soil organic carbon, and soil organic matter across the stand ages. Seven species were identified as indicators of the three stand ages. Redundancy analysis indicated that the Tugai forest diversity indices were negatively correlated with groundwater depth, groundwater salinity, and distance from the river, and positively associated with electrical conductivity, total salt, pH, Cl−, SO42−, CO32−, soil organic matter, soil organic carbon, and soil moisture content. Plant diversity was the highest at 3–6 m groundwater depth, followed by 0–3 m and then 6–9 m, with the lowest recorded at > 9 m. The appropriate groundwater depth for herbs was about 1–4 m, whereas the depth for trees and shrubs was about 3–6 m. The groundwater depth < 6 m was deemed suitable for the growth of desert riparian forests. This results provide a scientific reference for the ecological restoration and protection for Tugai forests in arid areas.

Riparian plant diversity in arid regions is sensitive to changes in groundwater. Although it is well known that groundwater has a significant influence on plant diversity, there have been few studies on how groundwater and soil salinity impact plant community in desert riparian ecosystems. Therefore, we surveyed 77 quadrats (100 m × 100 m) to examine the relationship between groundwater depth, groundwater salinity, soil salinity and plant community in the upper reaches of the Tarim River. Data were analyzed with two-way indicator species analysis (TWINSPAN), detrended canonical correspondence analysis (DCCA) and principal component analysis (PCA). The results indicated that Populus euphratica, Tamarix ramosissima, and Phragmites australis were the dominant plants among trees, shrubs and herbs, respectively. Five plant community types were classified. There were significant differences in species diversity, soil moisture, soil salinity, groundwater depth and groundwater salinity across the community types. The composition and distribution of plant community are significantly influenced by groundwater depth, groundwater salinity, soil moisture, distances from the river to the quadrats, soil pH, electrical conductivity, total salt, CO32−, Cl−, SO42−, Ca2+, Mg2+, Na+ and K+. Shallow groundwater depth, low groundwater salinity, and high soil moisture and soil salinity were associated with higher plant diversity.

In recent years, the climate in the arid region of Northwest China has become warmer and wetter, however, glaciers in the north slope of the West Kunlun Mountains (NSWKM) show no obvious recession, and river flow is decreasing or stable. This contrasts with the prevalent response of glaciers to climate change, which is recession and initial increase in glacier discharge followed by decline as retreat continues. We comparatively analyzed multi-timescale variation in temperature&ndash, precipitation&ndash, snow cover-runoff in the Yarkant River Basin (YRK), Karakax River Basin (KRK), Yurungkax River Basin (YUK), and Keriya River Basin (KRY) in the NSWKM. The Mann&ndash, Kendall trend and the mutation&ndash, detection method were applied to data obtained from an observation station over the last 60 years (1957&ndash, 2017) and MODIS snow data (2001&ndash, 2016). NSWKM temperature and precipitation have continued to increase for nearly 60 years at a mean rate of 0.26 &deg, C/decade and 5.50 mm/decade, respectively, with the most obvious trend (R2 &gt, 0.82) attributed to the KRK and YUK. Regarding changes in the average snow-cover fraction (SCF): YUK (SCF = 44.14%) &gt, YRK (SCF = 38.73%) &gt, KRY (SCF = 33.42%) &gt, KRK (SCF = 33.40%). Between them, the YRK and YUK had decreasing SCA values (slope &lt, &minus, 15.39), while the KRK and KRY had increasing SCA values (slope &gt, 1.87). In seasonal variation, the SCF of the three of the basins reaches the maximum value in spring, with the most significant performance in YUK (SCF = 26.4%), except for YRK where SCF in spring was lower than that in winter (&minus, 2.6%). The runoff depth of all river basins presented an increasing trend, with the greatest value appearing in the YRK (5.78 mm/decade), and the least value in the YUK (1.58 mm/decade). With the runoff response to climate change, temperature was the main influencing factor of annual and monthly (summer) runoff variations in the YRK, which is consistent with the runoff-generation rule of rivers in arid areas, which mainly rely on ice and snow melt for water supply. However, this rule was not consistent for the YUK and KRK, as it was disturbed by other factors (e.g., slope and slope direction) during runoff generation, resulting in disruptions of their relationship with runoff. This research promotes the study of the response of cold and arid alpine regions to global change and thus better serve regional water resources management.

Are desert ecosystems a stable sink for atmospheric CO 2 ? Although the uptake of atmospheric CO 2 by soil during the nighttime is detected in deserts and some semi-deserts, the underlying mechanisms remain elusive. In order to determine the factors affecting the CO 2 fluxes into soil and to reveal the relationship between CO 2 fluxes and carbonate formation and recrystallization in saline and alkaline soils, four soils with contrasting salinity from two sites, Aksu and Yingbazar, along the Tarim River were analysed. Soils were incubated in 14 CO 2 labelled atmosphere for 90 days at three CO 2 concentrations: 0.04%, 0.4% and 4%. The 14 C activity was measured in soil water and air, as well as in carbonates after 2, 14 and 90 days. The 14 C incorporation in CaCO 3 increased with corresponding 14 C decrease remaining in the CO 2 . The highest 14 C incorporation into CaCO 3 (54%) was observed in the Yingbazar saline soil. The carbonate recrystallization rates increased logarithmically (r 2 > 0.97) with the CO 2 concentration. The average carbonate recrystallization rate from three sampling times was highest in the Yingbazar saline soil under 4% CO 2 (8.45 × 10 − 6 day − 1 ) and lowest in the Aksu alkaline soil under 0.04% CO 2 (0.03 × 10 − 6 day − 1 ). The average carbonate recrystallization rate increased with electric conductivity (corresponding to soil salinity) but decreased with pH ( R 2 = 0.99 for 4% CO 2 ). The alkaline soils incorporated less 14 C into CaCO 3 than the saline soils. At the highest CO 2 concentration of 4%, the full recrystallization period of the remaining primary carbonates was 10- to 100-fold shorter than at the lower CO 2 concentrations. Therefore, besides soil chemical parameters (e.g. pH, CaCO 3 content), CO 2 concentration (respiration of microorganisms and roots) is an important factor for CaCO 3 recrystallization and formation of pedogenic carbonates in desert soils. It is the most important factor for CaCO 3 recrystallization and so, for the formation of pedogenic carbonates.

The simulation results of CMIP5 (Coupled Model Inter-comparison Project phase 5) multi-model ensemble in the Indus River Basin (IRB) are compared with the CRU (Climatic Research Unit) and APHRODITE (Asian Precipitation-Highly-Resolved Observational Data Integration Towards Evaluation) datasets. The systematic bias between simulations and observations is corrected by applying the equidistant Cumulative Distribution Functions matching method (EDCDFm) and high-resolution simulations are statistically downscaled. Then precipitation and temperature are projected for the IRB for the mid-21st century (2046–2065) and late 21st century (2081–2100). The results show that the CMIP5 ensemble captures the dominant features of annual and monthly mean temperature and precipitation in the IRB. Based on the downscaling results, it is projected that the annual mean temperature will increase over the entire basin, relative to the 1986–2005 reference period, with greatest changes in the Upper Indus Basin (UIB). Heat waves are more likely to occur. An increase in summer temperature is projected, particularly for regions of higher altitudes in the UIB. The persistent increase of summer temperature might accelerate the melting of glaciers, and has negative impact on the local freshwater availability. Projections under all RCP scenarios show an increase in monsoon precipitation, which will increase the possibility of flood disaster. A decreasing trend in winter and spring precipitation in the IRB is projected except for the RCP2.6 scenario which will cause a lower contribution of winter and spring precipitation to water resources in the mid and high altitude areas of the IRB.

As a key service for regulating ecosystems, soil conservation (SC) plays a critical role in preventing regional land degradation. However, there are few studies on SC services in Central Asia, and there is a lack of quantitative assessments of long-term time series. Meanwhile, future climate change is also expected to exacerbate the uncertainty in SC assessments in Central Asia. Based on this, we modified the revised universal soil loss equation (RUSLE) model applicable to the Central Asia region through the localizing parameters. This study represents the first comprehensive assessment to investigate the SC in the four major basins (FMB) in Central Asia (Amu Darya Basin, ADB; Syr Darya Basin, SDB; Ili River Basin, IRB; and Tarim River Basin, TRB) in the current period (1996–2015) and in the future (with global warming of 1.5 °C (GW_1.5 °C) and 2.0 °C (GW_2.0 °C)). The results indicate that the current and future SC in Central Asia generally show increasing trends, but these trends slow with increasing temperature. Compared with the current value, the future SC in Central Asia is 4.7% and 7.9% lower under GW_1.5 °C and GW_2.0 °C, respectively. The future SC in the FMB decreases under global warming of 2.0 °C (GW_2.0 °C), with the decreases in the basins exhibiting the following order: TRB (-15.1%) > SDB (-8.6%) > ADB (-4.6%) > IRB (-3.3%). With increasing elevation, the SC in Central Asia increases and then decreases. Moreover, under GW_1.5 °C and GW_2.0 °C, the areas with the most concentrated SC extend from the areas at elevations of 1500–3500 m to areas at higher elevations. Temperature and precipitation had a synergistic effect on SC in Central Asia. Among the FMB, the TRB is most sensitive to climate variability. As the temperature increases by 16.9% and the precipitation increases by 30.0%, the SC in the TRB decreases by 7.0% (20.3 t km−2). The SC in the TRB should be prioritized in the FMB in Central Asia under GW_1.5 °C and GW_2.0 °C. The present study fills the gaps in the study of SC services in Central Asia and improves the simulation and risk assessment of SC in arid regions.

Desert riparian plants experience high variability in water availability due to hydrological fluctuations. How riparian plants can survive with low water availability has been well studied, however, little is known about the effects of high water availability on plant community structuring. We conducted a mesocosm experiment to test whether seedling competition under simulated high groundwater availability can explain the shift of co-dominance of Populus euphratica and Tamarix ramosissima in early communities to P. euphratica dominance in mature ones along the Tarim River in northwestern China. Seedlings of these two plant species were grown in monoculture and mixture pools with high groundwater availability. Results indicated that the above-ground biomass and relative yield of T. ramosissima were higher than those of P. euphratica. The competitive advantages of T. ramosissima included its rapid response in growth to groundwater enrichment and its water spender strategy, as evidenced by the increased leaf biomass proportion and the inert stomatal response to leaf-to-air vapor pressure deficit (VPD). In comparison, P. euphratica showed a conservative strategy in water use, with a sensitive response to leaf-to-air VPD. Result of the short-term competition was inconsistent with the long-term competition in fields, suggesting that competition exclusion is not the mechanism structuring the desert riparian plant communities. Thus, our research highlights the importance of mediation by environmental fluctuations (such as lessening competition induced by disturbance) in structuring plant communities along the Tarim riparian zones.

The ecosystem along the lower reach of Tarim River has been undergoing remarkable changes due to the ecological water conveyance activity since 2000. To improve the scientific basis of riparian restoration, the clearing understanding of the dynamic of eco-hydrological system and the feedback between hydrological and ecological components are needed. A fully distributed eco-hydrological model combines a hydrology component based on the modified MODFLOW, with a vegetation dynamic component described by Verhulst logistic equation. The validation of the eco-hydrological model using groundwater well observation, river stage observation and remote sensing data demonstrated that the good capability of the model in simulating the dynamic of the eco-hydrological system in lower reach of Tarim River. The interaction between the hydrological component and ecological component has been revealed through water balance analysis and scenario studies. Vegetation has a significant impact on groundwater evapotranspiration, groundwater storage change and groundwater depth, while groundwater depth is a critical feedback variable that determines the vegetation dynamics, which is shown by observation and simulation result. The eco-hydrological model represented in this study could help to groundwater dependent ecosystem restoration and protection, particularly for riparian ecosystem.

The analysis of the principle of salt mass balance in irrigation districts is the foundation for the rational drainage system design and its effective evaluation. The salt balance of the Weigan River irrigation district is analyzed using annual measured data. Factors affecting the ratio of drainage to irrigation (RDI) and methods for determining this ratio are discussed. The results show that RDI is related to the volume and salt content of irrigation water and drainage water. The critical RDI for the Weigan River irrigation district is 9.29%. It is necessary to achieve a certain level of percolation to maintain the hydrosalinity balance when planning irrigation schedules and managing irrigation and drainage. Moreover, urgent improvement of the current drainage system is required to ensure that the actual RDI is greater than the critical RDI in the irrigation district. From 1994, the irrigation district turned from salt accumulation to desalinization, and the ratio of drainage to irrigation tended to optimal value.

According to the soil particles data, DEM elevation, slope, distance to river, distance along river, land use, and soil type for 95 typical sampling profiles along the Tarim river mainstream, the generalized linear models (GLMs) and generalized additive models (GAMs) are used to identify the spatial variability pattern of soil particles on the watershed scale and associated driving forces. The results show that the drainage basin sand, silt and clay content along the Tarim river mainstream all present moderate variability. The spatial pattern of soil particles is mainly subjected to the influence of gravity, hydrodynamic force, soil parent material and human activities. Modeling results show that the GAMs performs better than GLMs in regard to the explanation of total deviation. The contribution degree of GAMs for total deviation is 44.19 % (sand), 38.68 % (silt) and 37.46 % (clay). This major influence factors of soil particles distribution are land use, hydrodynamic force, soil type and terrain. The study has provided a way to explore aspects of spatial heterogeneity and to discover how spatial pattern controls the distribution of the soil particles.

The ecology in the Tarim River Basin is influenced by inundation of its floodplain. To date, however, there is limited information about the infiltration properties of floodplain soils that are inundated by this river. The aim of this study was to investigate steady-infiltration rates of these soils under four different hydraulic heads (5, 10, 20, and 30 cm). Results showed that the mean infiltration rates were generally high and ranged from 3.17 to 3.50 cm h−1 when the hydraulic head was between 5 and 30 cm. The steady infiltration increased slightly as the hydraulic head increased. The relationship between the hydraulic head and the infiltration rate can be described by the equation y = 0.0122x + 3.072, (R 2 = 0.739), where y is the steady-infiltration rate and x is the hydraulic head. There was no significant difference between the infiltration rates for the four different hydraulic heads. The infiltration rate was highest for loamy sand, followed by sandy loam, and was lowest for silt soils. Infiltration was influenced by soil texture and crust, and was low (

Summary The primary goal of this work was to identify the sustainable groundwater yield which is a key reference of reasonable groundwater development, but also a complex issue in current hydrogeologic science. One major limit to identify sustainable groundwater yield is the lack of a unified evaluation criterion because there are many factors involved in hydrological systems that are difficult to quantify. To address this problem, an integrated evaluation model was constructed for a series of purposes including the maximal efficiency of water use, the integral benefit of development and utilization, the optimized environmental water demand and the minimal anthropogenic influence on groundwater system. It consists of a benefit model, a water cycling simulation model and an optimization model. The basin-wide model for water cycling simulation was a basic component to simulate scenarios with different constraints, and the best water development strategy was thereafter identified using the integral benefit model of water resources development. The Yinma River basin in a Chinese semi-humid region was selected as the case study area. Results indicated the optimized groundwater yield could be sustained by intensive reservoir supply and maintain suitable ecological water demand simultaneously. The work proposed a potential groundwater utilization strategy for economically developing countries across the world.

Groundwater is widely recognized as the most significant water resource for irrigation and drinking purposes in the extremely-arid inland river region. However, land use is a major force altering the hydrological processes over a range of temporal and spatial scales. Therefore, understanding the interaction between land use and groundwater processes will definitely contribute to formulate a regional sustainable development strategy and recognize the impact of land use on the groundwater flow regime in the Tailan River basin. A numerical simulation of groundwater level for the inland river basin and scenario analysis under land use using FEFLOW is presented. Spatial data of the regional land use were processed using GIS, and the effects of land use on groundwater level were simulated. The amount of irrigation water and pumped groundwater have the most remarkable influences on groundwater level as main source/sink factors. Their variations were simulated according to the irrigation systems with different crops. Other factors including percolation and evapotranspiration of precipitation and condensed water jointly exerted influences on groundwater level. Changes to farmlands had the greatest impact on Tailan River basin for groundwater level, and unused land and Gobi had the least impact on groundwater level. Groundwater level maintained a decreasing trend in the irrigated zone, and increasing groundwater pumping would further intensify the water shortage in Tailan river basin. This coupled effects resulted from land use and extensive groundwater pumping were considered as the major human-induced factors influencing the groundwater system in the extremely-arid inland river basins. The results can provide useful support for land use. Understanding hydrological processes at the watershed level is essential in land use and water resource planning and management, and the proposed approach can be used as a management and planning tool for evaluating the local and overall impacts of land use management on the surface and groundwater flow regimes.

Monitoring soil CO2 respiration with chamber measurements and identifying controlling factors such as the diversity of vegetation species, moisture and temperature can help guide desert scrubland management. Soil CO2 respiration and potential controlling factors at four sites in desert scrubland were examined along the Sangong River Basin (SRB) in northwestern China in 2004. Soil CO2 respiration descended along the SRB as did the diversity of vegetation species, air temperature and air humidity. The two sites of the field station (FS) and the north desert (ND) and the low reaches of the SRB among these locations were monitored to analyze the effects of pH value, soil organic carbon (SOC), total nitrogen (TN) and calcium carbonate (CaCO3) on soil CO2 respiration during the growing season in 2005. The ND site was located at the southern edge of the Gurbantunggut Desert; the FS site was in the border area of the SRB Alluvial Fan. One-way ANOVA was performed. The result showed that air humidity and CaCO3 content had a strong influence on soil CO2 respiration; SOC content was a limitation to soil CO2 respiration in the arid-desert zone. Effective management activities can attenuate soil CO2 respiration and keep carbon balance trends at a desirabe level in desert scrublands.

The numerical models for predicting two-dimensional groundwater flow in the continental river watersheds were developed based on the water budget in the watershed, and by regarding the effects of groundwater depth on vegetation change as the source/sink factors. The vegetation changes patterns were classified into several types according to climatic conditions and groundwater depths in the desert regions. The source/sink factors such as volumes of irrigation water and pumped groundwater were found to have the greatest effects on groundwater flow. The variations of source/sink volumes were calculated in detail according to the irrigation systems for different crops. The other source/sink volumes associated with vegetation changes due to the vegetation type changes are of secondary importance, and they include mainly permeation and evapotranspiration of the limited precipitation and condensed water, and their volumes are distributed in the certain periods. The spatial data of the regional vegetation change were processed using GIS, and the effects of groundwater level on the vegetation change were simulated by combining the vegetation type changes with FEFLOW software. The results indicated that the groundwater level maintained a decreasing trend in the upper part of the marginal zone of fans and a continuously increasing trend in the alluvial–diluvial plains. This combined effect resulted in deterioration of vegetation on the upper part of the watersheds and a further soil salinization in the lower alluvial–diluvial plains.

Water and energy balance models were developed at the local and basin scale by aggregating a HYDRUS Model across scales in a topographic framework. A spatially distributed approach was followed to aggregate the HYDRUS Model to basin scale. The effects of spatial variability on the estimation of evapotranspiration at basin scale are emphatically discussed. In the present work the main emphasis was focused on the estimation of the spatial variability of both evapotranspiration and the calculation of statistical parameters of soil water storage from local scale to basin scale. Our results illustrate that the changes of the local and area-averaged potential evapotranspiration (ETp), actual evapotranspiration (ET) show a strong seasonal trend where the mean and standard deviation (STD) approximately fit the two-harmonics of Fourier series. Moreover, ETp and ET are random variables which follow the normal distribution with mean and deviation changing with season. A sensitivity analysis of the results shows that to a reasonable degree, the incorporated model can be used to determine the relationship between the actual area-averaged evapotranspiration and the main controlling factors for both bare soil and vegetated surfaces.

Riparian plants in arid regions face a highly variable water environment controlled by hydrological processes. To understand whether riparian plants adapt to such environments through plastic responses, we compared the root traits, biomass allocation and growth of Populus euphratica Oliv. Seedlings grown in lysimeters filled with clay or clay/river sand sediments under inundation and varying water table conditions. We hypothesized that adaptive phenotypic plasticity is likely to develop or be advantageous in seedlings of this species to allow them to adapt desert floodplain environments. Growth was significantly reduced by inundation. However, rather than following relatively fixed trait and allocation patterns, the seedlings displayed adaptive mechanisms involving the development of adventitious roots to enhance plant stability and obtain oxygen, together with a lower proportion of root biomass. At the whole-plant level, at deeper water table depths, seedlings allocated more biomass to the roots, and total root length increased with decreasing water table depths, regardless of the sediment, consistent with optimal partitioning theory. The sediment type had a significant effect on seedling root traits. P. euphratica displayed very different root traits in different sediment types under the same hydrological conditions, showing a greater first-order root number in clay sediment under shallower water table conditions, whereas rooting depth was greater in clay/river sand sediment under deep water table conditions. In clay sediment, seedlings responded to lower water availability via greater root elongation, while the root surface area was increased through increasing the total root length in clay/river sand sediment, suggesting that seedlings facing deeper water tables are not always likely to increase their root surface area to obtain more water. Our results indicate that P. euphratica seedlings are able to adapt to a range of water table conditions through plastic responses in root traits and biomass allocation.