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[Display omitted] • The changes in nineteen secondary LU types and their ESVs were predicted under the BAU and EDP scenarios by 2030 and 2050. • The LU pattern under EDP scenario is more conducive to the increase of ESV, with the increment by 2050 is 13.6 times that under BAU scenario. • Under the EDP scenario, the growth of ESV mainly comes from the positive contributions of the expansion of Forest (55.4%), Water (48.6%), and Grassland (19.1%). • Under the EDP scenario, the negative contributions of the decreases in Farmland and Unused land to the increment of ESV are −16.2% and −10.8%, respectively. The effects of land use/cover change (LUCC) on the spatial distribution and change of ecosystem service value (ESV) are still ambiguous, and cannot effectively guide the formulation of land use (LU) management policies based on the concept of harmonious development. Therefore, based on LUCC data from 1980 to 2020, this study adopted the MCE-CA-Markov model to simulate and predict the LUCC under the Business As Usual (BAU) and Ecological Development Priority (EDP) scenarios in 2030 and 2050. The historical and future ESVs as well as the effects of LUCC on ESV change were calculated in Gansu province, Northwest China. The results showed that the LU and ESV of Gansu province changed greatly between 1980 and 2020, with an increase in Forest (568.62 km2), medium- and high-coverage grassland (1517.58 km2), and Construction land (2264.58 km2), and a decrease in Farmland (-730.17 km2) and Unused land (-2858.58 km2), resulting in an increase of 8.162 billion CNY in total ESV. From 2020 to 2050, the LUCC under the EDP scenario will be more conducive to the increase in ESV, with the increment (52.765 billion CNY) being much higher than that under the BAU scenario (3.885 billion CNY). The growth of ESV will mainly result from the expansion of Forest, Water, and Grassland, accounting for 55.4%, 48.6%, and 19.1% of the total ESV increment, respectively, while the decrease in ESV will be attributed to the changes in Farmland and Unused land, accounting for −16.2% and −10.8% of the total ESV increment, respectively. The results have a certain reference for the future LU structure optimization and ecological benefit growth in northwest China. [ABSTRACT FROM AUTHOR]

• The hydrology changes is sensitive to energy in high-altitude. • The hydrology changes is controlled by water limitation in low-altitude area. • The water-energy coupling relation highly relies on altitudinal gradient. • Climate change dominate the hydrological shifts in alpine region. Hydrology heterogeneity refers to the different water regimes or hydrological processes in response to heterogeneous in topography, landscapes, land cover, soil properties, geology and meteorology reflecting as the spatial variation of precipitation, evapotranspiration and water yield along with landscape, elevation, terrain and climate variation. However, the hydrology heterogeneity in the alpine region of inland river basin has remained unclear to date, which limits the understanding of the hydrology and landscape interaction mechanism and affects the rational utilization of regional water resources. In this study, we combined the soil and water assessment tool (SWAT) and water-energy coupling framework to detect the hydrology heterogeneity in the arid alpine region of Heihe River Basin (HRB). We applied SWAT model to present the hydrological processes and regimes at different landscapes and elevation bands by using field measured parameters, and investigate the hydrology heterogeneity as well as the response to the changes in recent climate and land surface in the perspective of water-energy coupling framework. The results indicate that SWAT is indeed a robust tool in representing the streamflow process in alpine region with accurate performance. The distribution of landscapes reflect the comprehensive effect of regional water-energy coupling, which highly rely on the altitudinal gradient. The hydrology heterogeneity in high-altitude area is sensitive to energy and in low-altitude area is sensitive to water limitation (drought stress). Climate change is the dominate factor that driving the hydrology heterogeneity shifts in alpine region of HRB, while, the effect of land surface change is gradually strengthening over the past 50 years, reflecting with the contribution of land surface change on hydrology shifts is gradually increasing. [ABSTRACT FROM AUTHOR]

China's rapid population growth has inevitably led to a need for cropland expansion to meet food security challenges. In arid regions such an expansion is restricted by limited water resources, and an increase in productivity per cropland area must be achieved while still limiting water use. However, the response of agroecosystem Water Use Efficiency (WUE a. e.) to alterations in cropland use in Northwest China's Hexi Corridor has not been documented in any great detail. This has limited our understanding of the region's water-carbon interactions and, in particular, how effective cropland management and efficient water utilization protocols might be applied there. The response of the region's WUE a. e. to different potential shifts in cropland was evaluated by drawing on growing season (2003–2020), Gross Primary Productivity (GPP) and actual evapotranspiration (ET c act) data. Over this period net cropland area increased, with 12.3 % of total cropland transferred in, but only 2.5 % of cropland transferred out. The trend in growing season WUE a. e. was greatest in cropland regions transferred in (p < 0.05), and lowest in the cropland transferred out, indicating irrigation and field management in cropland could ensure that WUE a. e. could be maintained at a higher level. Among the different cropland transformation types, the impact of cropland change on WUE a. e. was essentially determined by shifting correlations between GPP and ET c act. This correlation was weakened when the water supply increased, heightening the negative impact of ET c act on WUE a. e. , while weakening the positive impact of GPP on WUE a. e.. There was a tradeoff point for the level of irrigation between improving WUE a. e. and crop yield. Suitable water-saving irrigation is crucial to maintaining a relatively high level of WUE a. e. , yet not decreasing crop yield. Water-saving irrigation in the Shiyang River basin was deemed to have limited potential, whereas in the Shule River and Heihe River basins there remains some potential for such irrigation. The present study's results can potentially inform agricultural water and land management in the region, and provide the basis for efficient water resources utilization. • Agroecosystem Water Use Efficiency (WUE a. e.) was evaluated considering cropland transformations. • The cropland transferred in (∆ CL ←) and out (∆ CL →) in Hexi Corridor was investigated. • The trend in WUE a. e. was the highest in the ∆ CL ← area, and lowest in ∆ CL → area. • The response of WUE a. e. to cropland change was regulated by the correlation of GPP and ET c act. • The correlation of GPP and ET c act is weakened along with an increase of water supply. [ABSTRACT FROM AUTHOR]

The nitrate pollution of groundwater in arid areas subject to human activity, and especially agricultural activity, is of immense environmental concern. Groundwater is the main water source in arid areas, once an aquifer is polluted, the impact upon the security of the water supply becomes all the more serious. The process of nitrate transformation is also different from that of humid areas, therefore, it is very important to identify and quantify the nitrate sources in aquifers. Using the hydrochemical, stable isotope tracers of 194 groundwater samples, and combining these with the MixSIAR model, the spatial distribution of groundwater nitrates in the Shiyang River Basin (SRB), China, was mapped. The relative contributions made by nitrate sources to different aquifers, and their key transformation processes, were identified. It was found that, shallow groundwater is seriously polluted, with NO 3 − concentrations ranging from 1.1 to 438.7 mg L−1. In the SRB, NO 3 − concentrations of 23% and 73% in shallow groundwater samples exceed the NO 3 − concentration limits found in natural sources (13.3 mg L−1), and the World Health Organization (WHO) nitrate limits for drinking water (50 mg L−1). Furthermore, the nitrates found in confined aquifers indicate that these are also affected by anthropogenic sources, with concentrations ranging from 1.6 to 44.7 mg L−1. Soil organic nitrogen (51.9%) and NH 4 + fertilizer (20.8%), wastewater and manure (20.5%) are the main sources of groundwater nitrates; NO 3 − fertilizer (4.4%) and precipitation (2.3%) have a relatively insignificant effect on groundwater nitrates. The process of nitrification is the main factor affecting changes in nitrate concentrations in aquifers. Other than the denitrification observed in the shallow aquifers of the Minqin Basin (MQB), there was no significant denitrification in the other sub-basins of the SRB. Anthropogenic sources, especially agricultural sources, are now major contributors to the increases in groundwater nitrate concentrations observed in the SRB. This study provides data that can be used to help prevent groundwater pollution and enhance water resources management in arid areas. [Display omitted] • Except Jinchang sub-basin, nitrate pollution in groundwater is obvious in other sub-basins of SRB. • Nitrate concentrations in confined aquifer have also been affected by anthropogenic sources. • The process of nitrification is the main factor affecting changes in nitrate concentrations in aquifers. • A denitrification process that would alleviate the nitrate pollution of groundwater bodies is relatively lacking in SRB. [ABSTRACT FROM AUTHOR]

The glacier is an important and stable water supply in Central Asia. Monitoring the change of glacier and understanding the impacts of glacier change on river discharge are critical to predict the downstream water availability change in future. Glacier changes were discussed and their impacts on river discharge were evaluated by hydrological modeling with a distributed hydrological model SWAT under two land use and land cover scenarios (1970 and 2007) in Tekes watershed, the most important source of water discharge to the Ili River. Compared to the glacier area of 1511 km 2 in 1970s it decreased by 332 km 2 in 2007, which resulted in the contribution the discharge from precipitation in the glacier area to the average annual discharge of the watershed changing from 9.8% in the period 1966–1975 to 7.8% in the period 2000–2008. In the month scale, with the decrease of glacier area, the distribution of the contribution of monthly discharge from precipitation in the glacier area to the total of the watershed changed from bimodal pattern to unimodal pattern. By linking a hydrological model to remote sensing image analysis and Chinese glacier inventories to determine glacier area change our approach in quantifying the impacts of glacier changes on hydrology at different scales, will provide quantitative information for stakeholders in making decisions for water resource management. [ABSTRACT FROM AUTHOR]

Model calibration is important for streamflow simulations using distributed hydrological models, especially in highland and cold areas of northwest China with scarce data. Quantitative analysis of water balance based on the accurate simulation is also essential for reasonably planning and managing water resources in these river basins facing a severe water shortage. In this study, a comprehensive method was proposed to calibrate the Soil and Water Assessment Tool (SWAT) model in the Yingluoxia watershed, upstream area of the Heihe River basin; it was based on multi-temporal, multi-variable and multi-site integrated drainage characteristics. Meanwhile a fresh approach of the parameter transferability and model validation was used by applying the set of calibrated parameters in its tributary to other area of the watershed. The results indicated that the method was effective and feasible; the values of Nash–Sutcliffe Efficiency ( NSE ) and Coefficient of Determination ( r 2 ) were greater than 0.81 and as high as 0.94 and the absolute values of the Percent Bias ( PBIAS ) were less than 2. Based the output of model the water balance in the Yingluoxia watershed was analyzed, that the mean annual precipitation, evapotranspiration, and discharge of the watershed from 1990 to 2000 were 491.8 mm, 334 mm, and 157.8 mm, respectively. The comprehensive calibration method based on multi-temporal, multi-variable and multi-site integrated drainage characteristics can better portray the hydrological processes of watershed and improve the model simulation; and the output of the model then provide a reliable reference for assessing and managing water resource of the watershed. [ABSTRACT FROM AUTHOR]

Terrestrial evapotranspiration (ET a) reflects the complex interactions of climate, vegetation, soil and terrain and is a critical component in water and energy cycles. However, the manner in which climate change and vegetation greening influence ET a remains poorly understood, especially in alpine regions. Drawing on the Global Land Evaporation Amsterdam Model (GLEAM) ET a data, the interannual variability of ET a and its ties to precipitation (P), potential evaporation (ET p) and vegetation (NDVI) were analysed. The Budyko framework was implemented over the period of 1982 to 2015 to quantify the response of ET a to climate change's direct (P and ET p) and indirect (NDVI) impacts. The ET a , P, ET p and NDVI all showed significant increasing trends from 1981 to 2015 with rates of 1.52 mm yr−1, 3.18 mm yr−1, 0.89 mm yr−1 and 4.0 × 10−4 yr−1, respectively. At the regional level, the positive contribution of increases in P and NDVI offset the negative contribution of ET p to the change in ET a (∆ET a). The positive ∆ET a between 1982 and 2001 was strongly linked with the concomitant increase in NDVI. Increases in vegetation contributing to a positive ∆ET a differed among landscape types: for shrub, meadow and steppe they occurred during both periods, for alpine vegetation between 1982 and 2001, and for desert between 2002 and 2015. Climate change directly contributed to a rise in ET a, with P as the dominant factor affecting forested lands during both periods, and alpine vegetation between 2002 and 2015. Moreover, ET p was a dominant factor for the desert between 1982 and 2001, where the variation of P was not significant. The contributions of factors having an impact on ∆ET a are modulated by both the sensitivity of impact factors acting on ET a as well as the magnitudes of factor changes. The greening of vegetation can influence ET a by increasing vegetation transpiration and rainfall interception in forest, brush and meadow landscapes. These findings can help in developing a better understanding of the interaction of ecosystems and hydrology in alpine regions. Unlabelled Image • ET a , P, ET p and NDVI showed significant increasing trends from 1981 to 2015 in QLM. • The positive contribution of increases in P and NDVI offset the negative contribution of ET p to the ∆ET a • Climate change contributed to a rise in ET a , with P as a dominant factor for forested lands. • Increase in vegetation dominated the positive ETa trends for shrub, meadow and steppe. • ET a was controlled by the sensitivity of factors to ET a as well as their change magnitudes. [ABSTRACT FROM AUTHOR]

One of the major components of the hydrological cycle, reference evapotranspiration (ET 0) represents the maximum amount of water transferred from the land surface to the atmosphere. Vital to quantifying crop water needs, accurate predictions of ET 0 are particularly critical in arid regions, where they allow for informed water resources management adjustments through changes to agricultural irrigation rates and scheduling. Drawing upon 84 meteorological stations in northwest China, spatiotemporal variations in present-day ET 0 were investigated. Support vector regression (SVR), Extreme learning machine (ELM), and Multivariate adaptive regression spline (MARS) — three machine learning (ML) techniques — served to establish relationships between historical ET 0 and the Coordinated Regional Climate Downscaling Experiment – East Asia (CORDEX-EA), drawn from the output data sets of each of three regional climate models (RCM): Weather Research and Forecasting (WRF), Regional Climate Model version 4.0 (RegCM4) and the Mesoscale Model version 5 (MM5). The ML-RCM combinations were calibrated and validated with separate batches (66:34, respectively) of historical ET 0 data, and their respective performance and level of uncertainty were assessed statistically. In the historical period (1960–2017) ET 0 declined by −0.15, −0.75, and − 0.42 mm y−1 in north Xinjiang, south Xinjiang, and Qinghai region, respectively, and increased in the Hexi Corridor by 0.5 mm y−1. For all four regions, the MARS-WRF and MARS-MM5 combinations performed well and showed greater predictive accuracy than either ELM-WRF or ELM-MM5 combinations. Performances in predicting future (2035–2050) ET 0 from CORDEX-EA outputs based on regional climate predictions RCP 4.5 and RCP 8.5 scenarios, depended to a greater extent on the RCM outputs that were selected, rather than the modeling methods. Future ET 0 predicted from RCMs generally exhibit increasing trends, and more significantly under the RCP 8.5 scenario. The representation and characterization ability of RCMs to future climate change is crucial for future ET 0 projection. Uncertainty analysis, achieved by employing multiple RCMs to predict future ET 0 , is highly recommended. Knowledge of trends in future ET 0 can help guide the management of agricultural irrigation in oases and support decision-makers engaged in water resources management in the future. • Historical ET 0 declined in Xinjiang, and Qinghai, and increased in Hexi Corridor, China. • The combination of MARS-WRF had the best predictive accuracy. • Prediction of ET 0 depends more on the RCM chosen rather than modeling methods. • Future ET 0 had an increasing trend, especially under RCP 8.5. [ABSTRACT FROM AUTHOR]

The relationship between climate and human society has frequently been investigated to ascertain whether climate variability can trigger social crises (e.g., migration and armed conflicts). In the current study, statistical methods (e.g., correlation analysis and Granger Causality Analysis) are used in a systematic analysis of the potential causality of climate variability on migration and armed conflicts. Specifically, the statistical methods are applied to determine the relationships between long-term fine-grained temperature and precipitation data and contemporary social conditions, gleaned from historical documents covering the last two millennia in China's Hexi Corridor. Results found the region's reconstructed temperature to be strongly coupled with precipitation dynamics, i.e., a warming climate was associated with a greater supply of moisture, whereas a cooling period was associated with more frequent drought. A prolonged cold period tended to coincide with societal instability, such as a shift from unification towards fragmentation. In contrast, a prolonged warm period coincided with rapid development, i.e., a shift from separation to unification. The statistical significance of the causality linkages between climate variability, bio-productivity, grain yield, migration and conflict suggests that climate variability is not the direct causative agent of these phenomena, but that climate reduced food production which gradually lead to migration and conflicts. A conceptual causal model developed through this study describes the causative pathway of climate variability impacts on migration and conflicts in the Hexi Corridor. Applied to current conditions, the model suggests that steady and proactive promotion of the nation's economic buffering capacity might best address the uncertainty brought on by a range of potential future climate scenarios and their potential impacts. Unlabelled Image • Cold periods coincided with social instability and the downfall of dynasties. • Causality linkages of climate-food-conflict were quantitatively justified. • Model for the pathway of climate change impacts on social systems was described. • Potential human integrated coping strategies with climate change are proposed. [ABSTRACT FROM AUTHOR]