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• This paper constructed a framework for green water assessment in the Loess Plateau gully region using MIKE SHE model. • A new concept and extraction method for green water components was defined based on existing research. • A new concept of the potential of green water was defined in relation to the dried soil layers' classification indicators. • We assessed the dependence on green water components and potential for environmental changes. Exponentially increasing water demand and increasingly uncertain hydrological conditions due to climate change (CC) and land use/cover change (LUCC) undoubtedly pose significant challenges to the sustainability of water systems in arid and semi-arid regions worldwide, and even more so in the rain-fed agricultural area of the Loess Plateau (LP) in China, where green water supports all ecological landscapes and most agriculture. Therefore, an accurate assessment of green water resources is crucial for regional development. This paper constructed a comprehensive framework for assessing green water resources based on the MIKE SHE model, defined a new concept of green water components (GWCs) that can be extracted based on existing studies, proposes the potential of green water (GW P), and present a research methodology. To validate this research framework, we applied it to a typical basin in the LP gully area of the Nanxiaohegou (NXHG) basin. The model was calibrated using runoff data from basin outlet stations to extract four GWCs: high-efficiency green water (GW H), low-efficiency green water (GW L), unused green water (GW U), ineffective green water (GW I). We then assessed the GW P of the basin and analyzed its trends, consistency, and dependence on changing environments. The assessment framework is simple and easy to use, providing valuable information for regional revegetation and basin water management, and is highly recommended for replication in other regions. [ABSTRACT FROM AUTHOR]

• A framework for analyzing urban resilience through the life circle lens was developed. • The spatial match between urban pressures and resilience was examined. • Strategies for a multi-center, cluster-type urban resilience typology were outlined. • A people-oriented resilient planning was advocated. This paper presents an original framework for assessing and enhancing urban resilience from the perspective of the life circle that emphasizes the daily activity spaces of residents, using Urumqi, a major city in northwest China's arid oasis region, as a case study. Based on multi-source urban geographic big data, we introduce Gini coefficient and Lorenz curve to analyze the spatial matching relationship between urban spatial pressure and urban spatial resilience, and divided the priority of planning intervention by priority index. Our findings for the case study Urumqi reveal a strong "center-periphery" structure of urban resilience and spatial pressures. Based on the findings, we proposed targeted planning interventions prioritized by a resilience index that considers the life circle to address disparities and improve urban resilience. Our study advocates for urban planning to focus on the life circle, aiming to develop a multi-center and cluster-type resilient urban spatial structure to foster a "people-oriented" resilient city. [ABSTRACT FROM AUTHOR]

Abstract In arid and semiarid regions of northwest China, there are abundant shallow coal reserves throughout the region, yet during the mining process, the shallow water resources available are typically depleted due to the formation of fractures in the shallow subsurface. Water-preserved mining is the only option for coal mining in arid regions of northwest China. Based on the geological and hydrogeological conditions of the study area, this paper investigates the basic conditions and mechanisms of goaf water storage. A time series model for goaf water storage is proposed, along with a method for estimating the quantity of goaf water storage. Finally, hydrochemical characteristics of mine water and water quality characteristics after purification in the study area were analyzed. As indicated by the analysis results, after simple purification, the goaf water can meet industrial, ecological and agricultural water consumption standards. In the end, combined with current monitoring results of goaf water pressure and the status of goaf water utilization in the study area, this paper describes the quantity and the effect of utilizing goaf water storage. Goaf water storage can effectively alleviate the scarcity of local production and domestic water, and provides the most effective approach of large-scale water-preserved mining of shallow coal seams in the arid regions of northwest China. [ABSTRACT FROM AUTHOR]

• Quantitatively describes the groundwater recharge process for lakes. • Constructed a model for the groundwater table-lake area relationship in groundwater-dependent lakes in arid regions. • Suggested a groundwater depth of 1.73 m to maintain stable lake area within the Hetao Irrigation District. • Constructed model can serve as an effective reference tool for groundwater management and the protection of lake ecosystems. The groundwater table constitutes a significant factor in sustaining the ecosystems of lakes in arid regions. To elucidate the mechanism by which variations in groundwater tables affect lake areas, this paper presents a case study of a typical groundwater-fed lake in China's Hetao Irrigation District. An analytical model correlating groundwater tables with lake areas was developed to simulate and predict the impact of changes in groundwater tables on lake areas. The findings indicate that the analytical model adeptly simulates the lake area dynamics of the groundwater-fed lake cluster (Taerhu lake cluster) from 1998 to 2018, achieving a Nash-Sutcliffe efficiency (NSE) value exceeding 0.6 and a root mean square error (RMSE) value below 0.1 square kilometers. Maintaining a groundwater depth at 1.73 m ensures the stability of the lake area; a decrease in groundwater depth to 1.93 m would result in a 79.5 % reduction in lake area. The model constructed in this study offers a crucial tool for the ecological protection of lakes and groundwater management in arid regions. [ABSTRACT FROM AUTHOR]

Oasification is a complex oasis expansion and ecological processes caused by climate changes and human activities under available water supply in arid and semiarid regions. The process can effectively improve soil productivity, vegetation cover, and biomass production in fighting against land degradation, such as desertification and soil erosion. However, the significance of oasification has not yet reached the general cognition compared to desertification, which is regarded as one of the most severe global eco-environmental issues. This paper identifies desertification and oasification processes and their perspectives in cognition. The implication of oasification in combating desertification and controlling land degradation is emphasized by the justification between desertification and oasification processes. As opposite process of desertification, the oasification is an unable evasive process that can provide positive environmental effects in the control of desertification, ecological restoration, and land rehabilitation. According to the interaction of climatic variations and human activities, the oasification processes is classified into six main forms: natural oasis evolution process, engineering forest construction, conversion of natural landforms into farmlands, urban encroachment, constructed environments, and coupled ecosystems. These processes gradually modify the productive capacity of soils, increase vegetation cover for restoring degraded lands, and improve the living environment for human settlement and sustainability of an oasis ecosystem. Moreover, an overview of oasification research is detailed, and Northwest China as an example is used to illustrate the progress of the oasification research in recent decades. Currently, the oasification process and its mechanistic research still remain less concern in the arid and semiarid regions. A new science framework of the oasification research is proposed to effectively deal with ecological and environmental issues in the arid and semiarid regions. • Desertification and oasification and their perspectives are identified. • Implication of oasification is emphasized in comparison with desertification. • Oasification processes are classified into six main forms. • Overview of oasification research is detailed and illustrated in Northwest China. • A new science framework of the oasification research is proposed. [ABSTRACT FROM AUTHOR]

Understanding the origins of groundwater and its movement from mountain to plain during different high intensity rainfall events is critical for conserving water supplies, determining water-use policies and controlling pollution. These factors are also the keys for understanding the dominant processes in hydrological models. In this study, groundwater resources and recharge processes during heavy precipitation were explored by using stable isotope tracers in the hilly area of Taihang Mountain. It was found that the δ2H and δ18O values of precipitation exhibited obvious precipitation amount effect during different precipitation intensity events. The stable isotopic values in groundwater and river water showed significantly varied during the single extreme heavy precipitation and the continuous heavy precipitation events. In the rainy season, precipitation amounts greater than 40 mm/d could effectively recharge the shallow groundwater in the study area. By comparing the spatial isotopic distribution of groundwater, soil water, and river water with precipitation, we showed distinct groundwater recharge patterns in terms of their water resources, timing, and the degree of river water and groundwater interaction during the single extreme heavy precipitation and the continuous heavy precipitation. After the single extreme heavy precipitation, the δ2H and δ18O values of groundwater, soil water, and river water showed stable over time and had the same similar variations, suggested that the groundwater recharge was mainly dominated by precipitation with preferential flow or bypass flow. While after the continuous heavy precipitation, the variation of δ2H and δ18O in all water is consistent with the previous precipitation, which shown a mixing effect of previous enrich precipitation and depleted heavy precipitation, suggested that groundwater source was dominated by a continuous recharge of previous heavier precipitation with translatory flow. The groundwater main recharge mechanism is not constant, but changes with rainfall intensity. The rainfall intensity play an important role in groundwater recharge change affecting runoff process. Overall, this paper presents a new insight to understand the effect of rainfall intensity on hydrological process, which could be used to provide vital information in the semi-humid and semi-arid regions where water resources are critical in climate change adaptation strategies. [Display omitted] • We identified the controls on groundwater recharge during different precipitation intensity events. • Precipitation greater than 40 mm/d could effectively recharge shallow groundwater. • Bypass flow after extreme precipitation produced stream water and groundwater recharge. • Groundwater recharge was by a continuous recharge with translatory flow after the continuous heavy precipitation. [ABSTRACT FROM AUTHOR]

The arid regions of northwestern China are dominated by extensive areas of mobile sand dunes. These features cause environmental problems and exert global climatic impacts; however, due to the lack of systematically-applied indicators of aeolian activity, direct evidence of past changes in aeolian activity is unreliable, especially for aeolian sand source regions. In this paper, we analyze the end-member (EM) distributions of various types of surface soil across the Tengger Desert in northwestern China, and devise a sensitive proxy for aeolian activity using a spatio-temporal substitution approach. This proxy is then used to evaluate a Quaternary aeolian succession and to understand the response of aeolian activity to regional climate change. Our results suggest that gradual increases in the coarse-grained EM components 3–5 reflect enhanced dune mobility and reduced vegetation coverage, which are a direct function of the intensity of regional aeolian activity. In the aeolian section, coarse- and medium-grained sand layers resemble modern semi-mobile and mobile dunes, whereas fine-grained sand layers are analogous to vegetated fixed/semi-fixed or semi-mobile dunes. Combining this record with independent multi-proxy evidence from the same section leads us to conclude that strong aeolian activity coincided with a dry climate, sparse vegetation cover, and strong surface winds during the Last Glacial Maximum, and that these conditions gradually attenuated at the beginning of the Last Deglacial. These inferences are in accord with independent paleoclimate records from this region, confirming that the intensity of aeolian activity in the southeastern Tengger Desert is closely associated with large-scale climate change. Our findings show that our EM proxy can be used to infer the intensity of aeolian activity and to reliably reconstruct the evolution of deserts in northwestern China. [Display omitted] • Coarse grain-size End-members (EM) 3–5 are a proxy of the strength of aeolian activity. • This proxy is applied to a palaeo-aeolian sequence to reconstruct the history of desert evolution. • Aeolian activity was closely associated with large-scale climate change. [ABSTRACT FROM AUTHOR]

Ecosystems in arid regions with sandy substrates are vulnerable to various environmental challenges. Understanding the vegetation evolution of such regions over a long timescale and the possible drivers of change is important for optimizing ecological restoration. In this paper, we present multi-proxy data to understand Holocene vegetation dynamics and their drivers in the Horqin Sandy Land in northern China. Phytoliths are used to reconstruct vegetation; grain size and magnetic susceptibility are used to reconstruct the climate; and sedimentary charcoal contents and the numbers of regional archaeological sites are used to reconstruct the fire activity and human activity intensity, respectively. Results indicate that the Horqin Sandy Land was covered mainly by grassland vegetation during the Holocene, and that the trajectory of vegetation evolution was as follows: sparse and species-poor Leymus chinensis grassland from 9300 to 6150 cal yr BP, relatively sparse and species-rich mesophytic herb grassland from 6150 to 2300 cal yr BP, and dense and species-rich L. chinensis grassland from 2300 to 250 cal yr BP. Climate change was the main driver of vegetation evolution, but fire and human activities also influenced the vegetation to varying degrees. Fire made the greatest contribution to the vegetation change during the 6150–2300 cal yr BP interval, and human activities contributed throughout the 8200–2300 cal yr BP interval. The evolution of plant species richness and the number of C 3 plants show a significant ∼1000-yr periodicity during 9300–4500 cal yr BP, which we speculate was caused by the effect of solar activity on East Asian monsoon intensity, which likely controlled the vegetation change on a millennial timescale. • The Holocene vegetation in Horqin Sandy Land is qualitatively reconstructed. • Climate dominated the vegetation evolution, while fire and human activity were additional influences. • The vegetation change shows a ∼ 1000-yr periodicity during 9300–4500 cal yr BP. • The vegetation change on a millennium cycle was likely driven by the solar activity. [ABSTRACT FROM AUTHOR]

The Soil and Water Assessment Tool (SWAT) model is diffusely applied to areas with uniform precipitation distribution and gentle slopes. However, the SWAT has apparent defects in the process of ecohydrological simulation in mid-high latitudes and arid regions. This model can merely be used in agricultural catchments with gentle slopes and uniform rainfall, and the simulation is not suitable for high-altitude alpine catchment. To this point, this paper makes appropriate improvements to the runoff module, and specifically corrects the key sensitive parameters. The global sensitivity and performance assessment of the model's parameters were carried out before and after the improvement using the monthly data of runoff and evaporation from 1990 to 2018 in the Kaidu River basin in northwestern China. It is indicated that the Modified SWAT simulates the performance of monthly runoff and evapotranspiration better than the original SWAT, which overestimates the runoff volume throughout hydrological changes in different periods. Compared with the monthly water production under different land use/cover conditions, the highest water production was found in forest and grassland. By modifying the SWAT algorithm, the structural non-determinacy of the Modified SWAT is significantly reduced, and the adaptability of the model is improved. Thus, the Modified SWAT shows a better simulation performance in arid areas with considerable terrain variation and scarce rainfall data. [Display omitted] [ABSTRACT FROM AUTHOR]

Understanding spatiotemporal urbanization is one of the key questions related to sustainable urbanization in the drylands of northern China (DNC). However, urban expansion in the DNC has not been quantified and assessed effectively due to a lack of reliable data and methods. In this paper, we investigate urban expansion in the DNC at multiple scales, ranging from the whole region to four dryland subtypes, and six urban agglomerations in the DNC from 1992 to 2015. We also simulate urban expansion in the DNC from 2015 to 2050 by coupling the scenario framework of the Shared Socioeconomic Pathways (SSPs) with the Land Use Scenario Dynamics-urban (LUSD-urban) model. Despite of the uncertainty in the research, our findings provide useful insight into the past and the future urban expansion in the DNC. The results indicate that the urban land in the DNC expanded rapidly from 4110 km 2 in 1992 to 20,969 km 2 in 2015. Furthermore, the urban land in the DNC will continue to expand from 20,969 km 2 to 22,987–36,622 km 2 by 2040, with an annual growth of 80.72–403.48 km 2 under all SSPs. Thus, it is suggested that effective measures are urgently needed to facilitate sustainable urban development in the DNC. [ABSTRACT FROM AUTHOR]

In recent years, climate extreme events have caused increasing direct economic and social losses in the arid region of northwestern China. Based on daily temperature and precipitation data from 1960 to 2010, this paper discussed the linear trend and abrupt changes of climate indices. The general evolution was obtained by the empirical orthogonal function (EOF), the Mann-Kendall test, and the distribution-free cumulative sum chart (CUSUM) test. The results are as follows: (1) climate showed a warming trend at annual and seasonal scale, with all temperature indices exhibiting statistically significant changes. The warm indices have increased, with 1.37%days/decade of warm days (TX90p), 0.17 °C/decade of warmest days (TXx) and 1.97 days/decade of warm spell duration indicator (WSDI), respectively. The cold indices have decreased, with − 1.89%days/decade, 0.65 °C/decade and − 0.66 days/decade for cold nights (TN10p), coldest nights (TNn) and cold spell duration indicator (CSDI), respectively. The precipitation indices have also increased significantly, coupled with the changes of magnitude (max 1-day precipitation amount (RX1day)), frequency (rain day (R0.1)), and duration (consecutive dry days (CDD)). (2) Abrupt changes of the annual regional precipitation indices and the minimum temperature indices were observed around 1986, and that of the maximum temperature indices were observed in 1996. (3) The EOF1 indicated the overall coherent distribution for the whole study area, and its principal component (PC1) was also observed, showing a significant linear trend with an abrupt change, which were in accordance with the regional observation results. EOF2 and EOF3 show contrasts between the southern and northern study areas, and between the eastern and western study areas, respectively, whereas no significant tendency was observed for their PCs. Hence, the climate indices have changed significantly, with linear trends and abrupt changes noted for all climate indices, which will have serious impacts on water resources and ecological environment in the arid region of China. [ABSTRACT FROM AUTHOR]

• Optical images are easily affected by clouds and cloud shadows. • Fmask is introduced into the GEE platform and modified for Sentinel-2 images. • The improved SNOWL algorithm considers unstable snow cover areas. • Snow cover extraction accuracy in flat surface and shady slope is the highest. • Snow cover in mountainous is reconstructed by combing the Fmask, Sen2Cor and the improved SNOWL algorithms. Snow is an important type of surface cover and an important freshwater resource in the arid regions of northwest China, and optical satellites are an important means for monitoring variation in snow cover. However, the radiation values measured by satellite sensors are affected by cloud cover and cloud shadows; thus, the reconstruction of snow cover under clouds and cloud shadows becomes a bottleneck problem especially in mountains areas. Based on the digital elevation model (DEM), in this paper, an integrated method of snow cover reconstruction on Sentinel-2 images is created by combining the improved SNOWL (snow line) algorithm considering unstable snow cover areas, Fmask cloud detection algorithms, and the Sen2Cor clear sky snow cover detection tool with a geospatial processing platform, GEE (Google Earth Engine). Considering the Babao River Basin as the study area, 474 Sentinel-2 scenes (10 m) were selected to obtain the snow cover spatiotemporal variations of 158 days from November 2016 to March 2021. Compared with the high-resolution GF-2 satellite images, the integrated method can extract snow under clouds and cloud shadows well, and the improved SNOWL algorithm improves the overall accuracy from 66.05 % to 84.26 %. The experimental results show that approximately half of the Babao River Basin is unstable snow cover, and areas above 3977 m are covered with snow for at least half a year. [ABSTRACT FROM AUTHOR]

Accurate estimation of reference crop evapotranspiration (ET 0 ) is important due to its crucial role in determining crop water requirement in irrigated agriculture. Though a great number of models have been developed, their rigorous evaluation with measurements is still lacking, leading to confusion and arbitrariness in model selection. In this paper daily estimates of 16 ET 0 models, including five combination-, six radiation and five temperature-based ones, were compared with weighing lysimeter measurements during crop growing season (April through October) in 2012 at a semiarid site in China. Daily ET 0 was measured by two weighing lysimeters (area 1.3 m × 1.3 m, depth 2.3 m) located in a fescue grass ( Festuca arundinacea Schreb) plot (100 m × 100 m) surrounded by a 167 ha crop, winter wheat rotated with summer maize. We found the models were ranked decreasingly as: FAO-ppp-17 Penman > 1963 Penman > FAO-24 Blaney-Criddle (BC) > 1996 Kimberly Penman > FAO-24 radiation > FAO-56 Penman-Monteith (PM) > FAO-24 Penman > Turc > DeBruin-Keijman > Jensen-Haise > Priestley-Taylor > Hargreaves > Makkink > Hamon > Blaney- Criddle > Mcloud on basis of RMSE (root mean square error). Overall, the combination models performed best with RMSE ranging from 0.93 to 1.32 mm d −1 , followed by the radiation models with RMSE from 1.28 to 1.79 mm d −1 , and the temperature models with RMSE from 1.09 to 2.48 mm d −1 . The best combination model (FAO-ppp-17 Penman) was respectively 29% and 17% more accurate than the best radiation (FAO-24 radiation) and temperature (FAO-24 BC) models. Better performance of the combination and radiation models resulted because they explicitly contain the dominant factors influencing ET 0 . All models tended to overestimate under low evaporative demand while underestimating the measured values under high demand, but on average the combination and radiation methods underestimated by 0.46 mm d −1 and 0.60 mm d −1 , respectively, whereas the temperature method overestimated by 0.21 mm d −1 . All combination and radiation models, and the Hargreaves and FAO-24 BC in temperature method showed robust structure. To improve them future efforts should be on local calibration, but for temperature models showing structure failure focus should be on its optimization. The coefficients of commonly used models were calibrated and related to meteorological variables. Particularly, those of the Priestley-Taylor, Makkink, Turc and the Hamon were enhanced, while those of the Hargreaves and BC were decreased. In climate similar to the current site in China we suggest continued use of the older Penman equations for combination method and the FAO-24 radiation or Turc for radiation method. Meanwhile, two questions need to be addressed in future studies: i) adoption of the FAO-56 PM equation as the sole standard for computing ET 0 and the proper value for surface resistance; and ii) the effectiveness of the later modifications to the original wind function in the Penman equation. [ABSTRACT FROM AUTHOR]

All activities are inherently risky, including seemingly beneficial activities such as ecological restoration. However, small risks are easy to ignore, even if they may accumulate to create a large cumulative risk. Therefore, the long-term ecological benefits and risks of any ecological restoration project must both be considered. However, quantitative evaluation of the risk of afforestation in arid and semi-arid regions has been insufficiently studied. Here, we present a method for evaluating the risk associated with ecological restoration, using water shortages in artificial woodlands in China’s arid and semi-arid regions as an example of cumulative risk. We found an annual risk that amounted to 5174 RMB ha −1 in 2014, which was 17% of the ecological service value of the forests. However, this cost depends on changes in the price, availability, and use of water in these regions. If ecological degradation occurs, it will trigger a series of serious consequences, and its cost may far exceed the expected benefits. Our inability to predict natural disasters such as drought and the problem of imperfect communication among stakeholders must be considered to achieve ecological restoration. The method described in this paper will provide theoretical support for future risk evaluations and guidance for the allocation of natural resources such as water, thereby increasing the likelihood of successful environmental management. [ABSTRACT FROM AUTHOR]

It is difficult – though important – to assess the necessary allocation of increasingly scarce water resources and yield estimation, by determining the exact amount of evapotranspiration ( ET ) and the partitioning of ET into transpiration ( T ) through the stomata of plants and evaporation ( E ) from the soil. An accurate and effective method for ET partitioning and estimation is, therefore, desirable. This paper aims to evaluate the performance of two main models for ET partitioning and estimation in terms of feasibility and accuracy: the AquaCrop (Version 4.0) model, and the SIMDualKc model. Field experiments were carried out between 2011 and 2015 in an arid region of Northwest China on two sites using full and deficit irrigation under plastic film-mulch, with the ET of maize for seed production and its partitioning components ( T and E ) being strictly measured by using the eddy covariance (EC) system or the sap flow system and micro-lysimeter cylinders. Subsequently, part of the measured data was used to calibrate the two models, so that the calibrated models could then be used to assess whether the agreement between simulation and measurement had proved successful, thus validating the models, or not. The results showed that the two models performed well with regard to their simulation of ET and T under full irrigation conditions. Under deficit irrigation conditions, the ET and T values simulated by the AquaCrop model were much closer to the actual measurement when compared with the results simulated by the SIMDualKc model. This was particularly the case when the soil was re-watered after a period of long-term water stress. For the simulated E , however, both models generated data that were distant from the actual measurements taken under full or deficit irrigation conditions using plastic film-mulch, although when the SIMDualKc model simulated E data, it came closer to the measurement than did the AquaCrop model. The comparison of two models in terms of their accuracy and feasibility based on the data analysis is discussed. [ABSTRACT FROM AUTHOR]

In recent years, ecological degradation caused by irrational groundwater exploitation has been of growing concern in arid and semiarid regions. To address the groundwater-ecological issues, this paper proposes a groundwater-resource exploitation mode to evaluate the tradeoff between groundwater development and ecological environment in the northern Tianshan Mountains, northwest China’s Xinjiang Uygur Autonomous Region. Field surveys and remote sensing studies were conducted to analyze the relation between the distribution of hydrological conditions and the occurrence of ecological types. The results show that there is a good correlation between groundwater depth and the supergene ecological type. Numerical simulations and ecological assessment models were applied to develop an ecology-oriented exploitation mode of groundwater resources. The mode allows the groundwater levels in different zones to be regulated by optimizing groundwater exploitation modes. The prediction results show that the supergene ecological quality will be better in 2020 and even more groundwater can be exploited in this mode. This study provides guidance for regional groundwater management, especially in regions with an obvious water scarcity. [ABSTRACT FROM AUTHOR]

The water resources in the arid region of northwestern China, which are impacted by climate change, tend to be more unstable, and the environment and ecosystems will suffer from severe water shortage. In this paper, potential future climate trends were predicted based on CMIP5 simulations in this region. The water availability and agricultural water demand under future climate change scenarios were estimated. Impacted by increases in temperature, the irrigation water demand will increase by 4.27–6.15 billion m 3 in this region over the next 60 years, compared to the demand of 32.75 billion m 3 during 1971–2000. However, the annual runoff will only increase by 4.8–8.5 billion m 3 , which is equivalent to or even less than the increased irrigation water demand. In fact, the increased demand for industrial, domestic and ecological water were not considered here. Thus, the water supply/demand contradiction will result in more severe water shortages in the future. According to a comparison with simulated irrigation water demand under three adaptation strategy scenarios, we should take effective measures such as improving the efficiency of irrigation water utilization, reducing crop planting areas and adjusting crop planting structures to alleviate the impacts of future climate changes and human activities on the water supply and water use in this region. [ABSTRACT FROM AUTHOR]

[Display omitted] • The proportion of vegetation improvement area in QLMs reached 65.06% in the past 21 years, while 52% of the area will be continuously improved in the future. • The distribution of the NDVI in the QLMs maintained a high spatial agglomeration. • Annual sunshine duration is the main meteorological factor affecting vegetation change in Qilian Mountains. • The interaction between different driving factors can improve the explanatory power of vegetation changes compared with a single driving factor. Vegetation is an important indicator reflecting ecological environment stability, and monitoring vegetation change and understanding its potential driving force have important guiding significance for the adjustment and implementation of ecological restoration measures. As an ecological security barrier in northwest China, the Qilian Mountains (QLMs) play an important role in promoting the green development of social and economic development. Currently, the comprehensive driving effects of natural and anthropogenic factors on vegetation change in the QLMs are not clear. Based on the normalized difference vegetation index (NDVI), the spatiotemporal characteristics and trend changes in vegetation in the QLMs were systematically analyzed from 2000 to 2020 in this paper. The effects of natural and anthropogenic driving factors on vegetation change were explored using a geographic detector (GeoDetector). The results showed that the vegetation has improved continuously in the past 21 years, but the overall vegetation coverage was still low. The vegetation distribution was highly clustered, with a decreasing trend from east to west. Annual sunshine duration (q statistic = 0.3347) and distance to the rivers (q statistic = 0.2649) had the greatest explanatory power for vegetation change, while slope, aspect, and landform type had the least explanatory power. The interaction between elevation and sunshine duration, temperature and precipitation, temperature and sunshine duration, elevation and precipitation had the most explanatory power for vegetation change. Finally, we determined the ranges or categories of driving factors that were most suitable for vegetation growth by using a risk detector. The results of this study can help us further understand the potential driving mechanism of vegetation coverage variation in the QLMs and provide theoretical guidance for relevant managers to formulate ecological restoration measures and land management policies in the next step. It is of great significance to maintain the stability of the fragile ecological environment and prevent land degradation in arid and semiarid areas of Northwest China. [ABSTRACT FROM AUTHOR]

• Spatiotemporal variation in vegetation on the Loess Plateau was investigated. • Precipitation was the greatest driving factor. • There was a bivariate or nonlinear enhancement between all factors. • Key factors' adaptation range or type suitable for vegetation cover was identified. Vegetation, being a core component of ecosystems, is known to be influenced by natural and anthropogenic factors. Studying vegetation cover dynamics variation and its drivers is critical to understanding the interactions between vegetation and ecosystems. The Loess Plateau (LP) is located in a semi-arid and semi-humid region with severe soil erosion and fragile ecology. This paper used the annual maximum Normalized Difference Vegetation Index (NDVI ymax) and growing season mean NDVI (NDVI gsmean) as the vegetation cover indicator. The vegetation cover variation of LP from 2000 to 2020 was analyzed using Sen's slope and Mann-Kendall test. Then the influence of natural and anthropogenic factors on the driving mechanisms of spatial vegetation differentiation was explored by the Geodetector model. The results revealed that the growth trends of NDVI ymax and NDVI gsmean were 0.075/10 years and 0.038/10 years, respectively, and the areas with improved vegetation cover accounted for 92.67 % and 88.58 % of the total area. The vegetation cover of the southeastern and northern parts of the LP decreased significantly; however, the central, southwestern, and northeastern parts exhibited a remarkable improvement. Precipitation, vegetation type, soil type, temperature, and land use type were the key driving forces, ranked differently on NDVI ymax and NDVI gsmean. However, precipitation was the most critical factor both on NDVI ymax and NDVI gsmean. The interaction detection showed non-linear and mutual enhancement, with no independent factor. The findings of our study can assist in identifying the vegetation cover status of the LP, as well as the driving forces, which can provide theoretical support for the formulation of environmental conservation policies. [ABSTRACT FROM AUTHOR]

• Both GPP and GPP max in Chinese grasslands showed increases at different space–time scales. • Trend analysis and breakpoint tests were used for the first time to monitor GPP change simultaneously in Chinese grasslands. • GPP max × CUP is a robust indicator to explain annual-scale variation in GPP. At the ecosystem level, Gross Primary Productivity (GPP) was defined as the organic compounds formed by plants that absorb atmospheric CO 2 through photosynthesis and sequester carbon in plant bodies. How to accurately assess the spatiotemporal evolution of ecosystem carbon indicators has become a critical issue to be addressed. Chinese grasslands are located in a typical arid and semi-arid climate zone and are sensitive to global changes, which will inevitably have serious impacts on the function and structure of Chinese grasslands. Based on this, our paper takes Chinese grassland ecosystems as the research area, and used multi-source GPP dataset from terrestrial ecosystem model simulations and remote sensing satellite observations to quantitatively analyze the spatiotemporal evolution patterns of GPP in Chinese grasslands over the past 40 years. We combined trend analysis and breakpoint test, and then to analyze the mechanism components of GPP space–time variability. The main results are as follows: (1) The model and remote sensing estimated GPP results showed that more than 80% of Chinese grasslands show a significant increasing trend over the past 40 years, with growth rates ranging from 0.68 to 3.13 g C/m−2 year−1. (2) GPP max also shows that more than 80% of Chinese grasslands are growing rapidly, with an overall growth rate of more than 0.1 g C/m−2 year−1 in each region. The overall long-term trends and interannual variability of multi-source GPP and GPP max are generally consistent, yet vegetation dynamics in local areas are still uncertain. (3) The breakpoint test showed that 'monotonically increasing' was the largest breakpoint type of GPP in Chinese grasslands (33.09%), and the direction of change of GPP in Chinese grasslands before and after the breakpoint was also increasing. (4) GPP max × CUP explained 91% of the temporal variability of annual-scale GPP in Chinese grasslands from a mechanistic view, and we found that the peak photosynthetic growth and the length of the phenological period synergistically controlled the interannual variability of GPP in Chinese grasslands. Under the scenario of rapid global change, our study accurately assessed the long-term dynamics of GPP and its mechanism-driven of grassland ecosystems in China, which is helpful for estimating and predicting the carbon budget of grassland ecosystems in China, and has important guiding significance for policy formulation to mitigate climate change. [ABSTRACT FROM AUTHOR]

In their thoughtful paper entitled "An equable subtropical climate throughout China in the Miocene based on palaeofloral evidence", Qing Wang, Yan Li, David K. Ferguson, Wen-Bo Mo, and Nan Yang (2021) imply that China exhibited negligible latitudinal mean annual precipitation (MAP) gradients and lacked arid regions during the Miocene. They also speculate that there was no abrupt change in elevation of the Tibetan Plateau, nor that the plateau attained its present altitude or orography during that period. These conclusions were derived mainly by using a co-existence approach (CA) and 'incomplete data'. Here, we use CA with training data and also integrate a coexistence likelihood estimation, a pollen-MAP boundary, a desert-MAP boundary, and other newly published MAP data to show that Northwest China consistently exhibited drier conditions than South China and East China during the entire Miocene, with our new values being 300–500 mm lower than those of Wang et al. (2021). This implies that there were large spatial gradients of MAP in China during the Miocene, which may be directly linked with the growth of the Tibetan Plateau, the global cooling, as well as other factors. We recommend the comprehensive consideration of multiple methods and proxies for reconstructing past climate conditions as opposed to a single proxy. [ABSTRACT FROM AUTHOR]

Desertification and salinization are both threats to the ecosystem services in inland river oases of arid regions. Previous studies focus on either desertification or salinization, and there is a lack of joint studies on the two issues. The essential cause of desertification in a transition zone is usually concentrated irrigation water use, which leads to shrink of the subsurface flow field of groundwater, decline of the groundwater level, and loss of groundwater supply to the vegetation. The salinization problem in an oasis area is mainly caused by the local excess groundwater in the oasis, referring to secondary salinization, which leads to salt migration with the groundwater level rise to form salt crystallization at the land surface. Thus, the processes of desertification and secondary salinization are connected, and the solutions to the two problems can be complementary, i.e., by transporting the excess groundwater in the local secondary salinization area to the transition zone area where water is scarce. This paper, taking Luocheng Irrigation District in the Heihe River Basin of northwestern China as an example, estimates 1.76–4.70 million m3 of excess groundwater that can be extracted in the salinized area. Using this amount of water through engineering regulation, it is estimated that the transition zone nearby the irrigation district, which is under desertification threat, can be restored with an area of 23–212 km2. An engineering system is designed for coordinated groundwater regulation and the implementation with an experimental farm in the irrigation district is demonstrated. • Providing a new method to mitigate salinization and desertification in arid areas through groundwater regulation. • Estimating the amount of drainage from salinized oasis area in an irrigation district and the transition zone area to be recovered from desert. • Designing an engineering system for coordinated groundwater regulation. [ABSTRACT FROM AUTHOR]

The role of vapor flow in unsaturated freezing soils is unclear, and usually ignored when analyzing water migration. Indeed, vapor flow is seldom considered in geotechnical design. On the other hand, frost heave damages were recently observed in a cold and arid region in China, where the groundwater table is about 20 m deep, and cannot be explained using the classical frost heave theory which focuses on the coupled flow of heat and liquid water. This paper presents a new approach for modeling moisture and heat movement in unsaturated freezing soils, in which the phase change of evaporation, condensation of vapor flow are taken into account. The method enables numerically stable solutions with energy and mass conservation. The performance of the proposed model was evaluated by a series of laboratory freezing experiments, which involve a 60 cm long soil column subjected to different initial conditions and boundary temperatures. It is shown that the proposed model is capable of effectively simulating the freezing process of an unsaturated soil. The vapor flux is shown to be significant, especially at the end stage where the freezing process is stabilized. Parametric analysis was carried out to clarify the role of vapor in moisture migration. The results show that vapor flow apparently contributes to ice formation and generally accounts for more than 10% of total water flux. The percentage of vapor flux in total flux (vapor flux ratio) positively relates to temperature gradient and freezing depth, but negatively relates to initial water content. Relations between vapor flux ratio and hydraulic parameters are less clear. [ABSTRACT FROM AUTHOR]

The Heihe River Basin (HRB) is the second largest inland river basin in the arid region of northwestern China. An agricultural oasis is a typical landscape in arid regions providing precious fertile soil, living space and ecological services. The agricultural oasis change has been one of the key issues in sustainable development in recent decades. In this paper, we examined the changes in the agricultural oasis in HRB and analyzed the socio-economic and climatic driving forces behind them. It was found that the agricultural oasis in HRB expanded by 25.11% and 14.82% during the periods of 1986–2000 and 2000–2011, respectively. Most of the newly added agricultural oases in HRB were converted from grassland (40.94%) and unused land (40.22%). The expansion in the agricultural oasis mainly occurred in the middle reaches of HRB, particularly in the counties of Shandan, Minle, Jinta and Jiuquan city. Changes in the rural labor force, annual temperature and precipitation have significant positive effects on agricultural oasis changes, while the ratio of irrigated agricultural oases has significant negative effects on agricultural oasis changes. The agricultural oasis expansion in HRB is the combined effect of human activity and climate change. [ABSTRACT FROM AUTHOR]

[Display omitted] • SIF data that characterizes the growth of sandy vegetation is more sensitive. • SIF can well capture the changes in surface moisture and groundwater. • Vegetation growth has a strong correspondence with SM and a relatively weak correlation with TWS. • Vegetation growth in the late period of the mutation year is generally better than that in the early period. • Similarities and differences of vegetation-moisture relationship in four sandy lands. Hulunbuir, Otindag, Horqin and Mu Us are the four greater sandy lands in China. They are typical ecologically fragile areas with limited ability to resist interference and are susceptible to changes in the external environment. With climate change in recent decades, these areas have experienced severe land desertification and decreased groundwater levels. The ecological environment is at risk of further deterioration, and continuous vegetation restoration and management should be adapted to the local climate and maintain the water balance with natural precipitation. This paper combines multi-source satellite observations to explore the relationship between vegetation growth and water supply. The results show four main points. (1) Although the vegetation growth in Otindag and Horqin had degraded before 2010, it improved after 2010. The vegetation growth and soil moisture (SM) of the four sandy lands both generally increased from 2003 to 2016. The SM of the Horqin increased significantly (84% anomaly > 1.4 × 10−2 cm3/cm3). Other than the Hulunbuir, the other sandy lands show a downward trend in terrestrial water storage (TWS), especially the Mu Us declined the most (97% anomaly < −40 mm). (2) Solar-induced chlorophyll fluorescence (SIF) has specific advantages in characterizing the sandy vegetation productivity and water composition changes compared to vegetation index (EVI) or gross primary productivity (GPP). (3) The regional pattern of the vegetation-moisture relationship is mainly affected by the precipitation-driven SM and depends on the types of underlying vegetation functions. (4) Both SM and TWS have approximately one-month persistence in the four sandy lands, especially the Mu Us has the longest persistence (0.94 months and 1.1 months). The persistence in the early period is generally longer than that in the late period, implying that the resilience of water components after the mutation year is stronger than before it. This study provides a scientific basis for the management and restoration of sandy lands. It is recommended that different vegetation restoration and protection strategies should be developed for specific sandy land moisture conditions in arid/semi-arid regions of northern China, which includes the improvement of water use efficiency to maintain soil moisture and the reduction of excessive groundwater uses. [ABSTRACT FROM AUTHOR]

The determination of spatiotemporal variation in ecosystem service value and its drivers is fundamental to ecosystem service management and decision-making. This paper selects a typical oasis irrigation district in the arid regions of northwest China as the research object. Using the benefit transfer method to evaluate the ecosystem service value variation caused by land use and land cover change and characteristics of its spatial distribution based on multi-temporal land use and land cover data sets (1977, 1987, 1997, 2007, 2017). Meanwhile, the contributions of factors driving ecosystem service value and their interactions were explored using geographical detector. The results showed the following: 1) The land use and land cover structure was stable from 1977 to 2017, and the overall ecosystem service value increased slightly. The services provided by the oasis ecosystem dominated the fluctuations in ecosystem service value throughout the study region. 2) Ecosystem service value exhibited a strong positive spatial autocorrelation. The high values were concentrated in the oasis area in the north of the study area, while the low values mainly appeared in the desert ecosystem. 3) The land use degree and human activity intensity index of human factors are the main factors leading to the differentiation of ecosystem service value. Synergized interactions among human activities, changes in landscape patterns, and natural factors produced the spatial differentiation in ecosystem service value of the study region. The results suggest that in future decision-making for ecosystem management, the direction of human activities within the ecological environment should be controlled. Improve the diversity of patches, reduce the degree of landscape fragmentation, improve the ecosystem service function of LULC, optimize the allocation of ecological landscape resources. [ABSTRACT FROM AUTHOR]

[Display omitted] • Grassland degradation is the main reason for the decline in carbon storage. • The carbon storage of farmland has increased significantly. • The risk of carbon storage reduction in the future is still high. The carbon storage of terrestrial ecosystems is closely related to global climate change. Therefore, assessing the impact of land-use changes on carbon storage is instructive to reduce global carbon emissions. Taking an arid region in northwest China as an example, this paper analyzed the land-use changes in arid region from 1980 to 2015. It used the CA-Markov model to predict the land-use pattern from 2020 to 2050, the carbon storage and sequestration module in Integrated Valuation of Ecosystem Services and Tradeoffs (Invest) mode to assess and predict ecosystem carbon storage over the past 35 years and in the next 30 years and discusses the impact of land-use changes on the carbon storage of terrestrial ecosystems. The results showed that: (1) The high-value areas of carbon storage in arid region were primarily concentrated in grassland, forests and farmland, and the low-value areas of carbon storage were mainly in desert areas. (2) The carbon storage in arid region showed a downward trend. From 1980 to 2015, the carbon reserves of terrestrial ecosystems in arid region decreased by 90.95 Tg, and the net loss of carbon reserves from 2020 to 2050 was 14.72 Tg. Grassland degradation was the main reason for the reduction of carbon storage in arid region. (3) The carbon storage of farmland had increased significantly, but the expansion of farmland dominated by high carbon density grassland, wetland and forest, had reduced the overall carbon storage of the arid region. [ABSTRACT FROM AUTHOR]

As the rapid development of economy, hydropower, as a kind of cleaner energy, is bringing in huge economic benefits, leading to the appearance of a great many of hydropower plants. Decades after the hydropower plants operation, series of quite serious ecological problems were brought in due to the changes in the natural flow. To restore the river ecosystem, this paper is making efforts on seeking series of operation schemes to balance the socio-economic and ecology benefits. Therefore, a simulation (Model-I) and an optimization (Model-II) operation model are established to provide a feasibility and a reasonable scheme for the multi-objective long-term and mid-term hydropower plant operation. To resolve the complex model, large-system coordinated decomposition method and an idea that efficiently narrows down the search space are used. The Irtysh River basin in China is selected as the study area to apply the model and make a trade-off to balance the water supply for socio-economics and ecology. The results show that the average annual power generation of hydropower plant group in Model-I is 2.5% more than that in Model-Ⅱ, both more than that of practical operation. In Model-I the water supply in dry year is far less than the minimum need (50%), but the Model-II provided a reasonable solution that the water supply in dry year is close to the median need (80%). Besides, the water supply for ecology in Model-II is obviously increased compared with Model-I, and the ratio increases from 56% to 86%, at the same time, the ratios to socio-economics are from 92% to 98%. Specially, the ratio of agricultural irrigation increases from 84% to 94%. In a word, the scheme meets the water requirements for socio-economics and ecology under considering the hydropower plants benefits, providing a scientific theoretical basis for water resource management. [ABSTRACT FROM AUTHOR]

In Shanxi Province, China, groundwater is a major problem and exploration of groundwater potential zones (GWPZs) is a great necessity. This paper contributed to integrate RS-GIS to delineate GWPZ and applied Fuzzy-AHP method in a single platform. The main objective includes delineation GWPZs with RS and geo-environmental factors using Fuzzy-AHP method. Fuzzy-AHP method was employed to calculate weight of factors. RS-GIS was used to create maps and discover groundwater availability. GWPZs were classified in five separate classes. Results indicated that 13.26%, 27.02%, 26.35%, 23.64%, and 9.71% area classified as very good, good, moderate, poor, and very poor GWPZs. The validated analytical results revealed 82.5%, 12.3%, 3.5%, and 1.7% existing water wells exhibited in very good, good, moderate, and poor/very poor GWPZs. This indicates Fuzzy-AHP model generated findings were in very good agreement with ground-truth data. This RS-GIS based Fuzzy-AHP method is proficient and efficient in identification and delineation of GWPZs. Image 1 • Groundwater potential zones (GWPZs) in semi-arid area delineated with RS-GIS. • Seven geo-environmental factors are used for GWPZ. • RS-GIS for GWPZ and Fuzzy-AHP model are used in a single platform. • Fuzzy-AHP method was employed to calculate the weight of the factors. • GWPZs are classified as very good, good, moderate, poor, and very poor GWPZ. [ABSTRACT FROM AUTHOR]

• Water deficit and low N reduced grain yield and flag leaf photosynthesis. • WUE, grain protein significantly improved and NUE, PFPN significantly decreased with N under water-deficit. • Newer genotypes showed higher NUE and WUE under water deficit combined with low nitrogen. • PCA showed that newer genotypes are more sensitive to low nitrogen and water stress. • As per PCA older cultivars are more sensitive to the combined effect of water and N. Although soil water and nutrients are two of the most important factors affecting growth and production of winter wheat, genetic improvement for wheat responses to water and nitrogen (N) levels has been rarely studied. In this paper, five dryland winter wheat cultivars representative of widely cultivated varieties released from the 1940s to the 2010s in Shaanxi Province, China, were grown in an open rainout shelter (which could be closed when rain threatened) under four contrasting water/N treatment combinations. Yield-related parameters, biomass accumulation, crop water productivity (WUE), and nitrogen use efficiency (NUE) were determined. The results indicated that water deficit and low N treatment caused a significant reduction in grain yield and flag leaf photosynthesis in the five wheat cultivars studied. However, NUE, grain protein content, and partial factor nitrogen productivity were significantly improved by N application under water deficit. Our results confirm the genetic improvement for plant growth, N accumulation, and grain yield in wheat cultivars released from the 1940s to the 2010s; newergenotypes showed the highest NUE under water deficit combined with N limited conditions. Additionally, based on principal component analysis, we found that the newer genotypes, i.e. those from the 2000s and the 2010s, are more sensitive to low nitrogen and water stress compared with the older genotypes from the 1980s, which are more sensitive to the combined effect of water and N limitations. Our findings provide a theoretical support for further improvement of the wheat yield potential, selection, and breeding of high-efficiency varieties in arid and semi-arid areas. [ABSTRACT FROM AUTHOR]

Dust storm originates from arid and semiarid areas and could cause worldwide lasting effects along varying trajectories. As an extreme weather hazard, dust storm is usually induced by strong winds. In this paper, an aerodynamic parameter, defined as the ratio between dust storm frequency (DSF) and strong wind frequency (SWF), was calculated for quantifying dust storm susceptibility (DSS). The characteristic value and temporal change of DSS in five typical land surface areas, including cultivated land, grassland, sand desert, Gobi desert, and salt crust, were analyzed with dust storm and strong wind records at 15 weather stations. The spatial distribution of DSS in the arid and semiarid regions of northern China was described using dust storm and strong wind records at 102 meteorological stations. There are positive correlations between SWF and DSF for any identical land surface type. Land surface conditions have a great influence on dust storm susceptibility. According to DSS value, the five land surface types can be divided into two categories: (1) Cultivated land and sand desert, with DSS between 0.64 and 0.53, about 2.6–10 times higher than that of the other three land surfaces, are prone to forming dust storm under strong wind conditions; (2) Gobi desert, grassland and salt crust, with average DSS from 0.06 to 0.2, exhibit lower probability of dust storm occurrence under strong wind conditions. The DSF in the surrounding areas of the arid Taklimakan desert in Xinjiang are much larger than SWF, and dust storms take place readily even at normal erosive wind conditions. The areas with high DSF are not spatially consistent with SWF distribution but more coincide with high DSS areas where sand deserts and farmland are concentrated. In the nearly four past decades, the DSS showed an overall increasing trend on different ground surfaces which may be related to local human activities and climatic warming. • There is positive correlation between strong wind and dust storm frequency • Dust storm susceptibility is the ratio between dust storm and strong wind frequency • Land surface conditions have great influences on dust storm susceptibility • Farmland, sand desert have higher dust storm susceptibility than other land surface • Dust storm frequency is spatially consistent with dust storm susceptibility [ABSTRACT FROM AUTHOR]

• Provides a timely overview on theoretical and methodological advances in loess study. • Encloses evolution and surface processes of loess landform and deposition environment. • Investigates impacts of fault activities and geohazards in loess areas of China. Loess is a type of Quaternary sediments of the wind origin in arid and semi-arid regions. This type of sediment is widely and thickly distributed in China, forming the Loess Plateau, which is the largest bulk accumulation of loess on the Earth. The Loess Plateau of China has received great attention from scientific communities, including geologists, geophysicists and engineers worldwide. Accordingly, a wealth of investigations has been undertaken on various problems arising in this area. However, some scientific questions remain relevant and unresolved. These questions mainly present in the areas of evolution and surface processes of loess landform, depositional environments of loess sediments, impacts due to Neotectonics and fault activities in loess areas, and natural and man-made geohazards. In recent years, extensive innovative studies have been carried out to further understand the above-mentioned topics. Substantial new data, theories and insights have become available. This special issue provides a timely overview on the recent case histories, theoretical advances, laboratory and field testing and state-of-art methods in the theme of loess geology and surface processes. The papers gathered in this special issue are introduced in this article. [ABSTRACT FROM AUTHOR]

• A method of estimating the long-term irrigation water consumption of irrigated cropland at the regional scale was proposed. • The spatial pattern and trend of irrigation water consumption in China from 1982 to 2015 was quantified. • Highly expanded irrigated farmland dominates the significant increase in total annual irrigation water consumption of irrigated cropland in China (67.2%±5.6%, 64.9%±4.7%). • The increased amplitude of annual total blue water consumption in the arid zone was higher than that in the humid area. Quantifying and mapping regional and global irrigation water consumption have attracted considerable attention from researchers. The existing models cannot accurately estimate the long-term sequence of irrigation water consumption at the regional scale. Despite being among the countries with the largest irrigated areas, China has not been specifically evaluated in terms of high-resolution long-term irrigation water consumption. In this paper, an irrigated cropland water model incorporating irrigated cropland mapping, the soil water balance equation, irrigated crop phenology, and partitioning evapotranspiration products was developed to fill the knowledge gap. We found that (1) the mean annual total irrigation water consumption of irrigated cropland in China during 1982–2015 was approximately 179.43 ± 24.60 km3. (2) The continued expansion of irrigated farmland dominated (67.2% ± 5.6%) the significant increase in annual total irrigation water consumption (slope=2.03 km3 yr−1, p <0.01), followed by changes in crop management practices (16.7% ± 6.1%), and the impacts of interannual climatic variability (represented by precipitation and potential evapotranspiration in this research) were weak. (3) The annual total irrigation water consumption in the arid zone increased quicker than that in wet regions. [ABSTRACT FROM AUTHOR]

This paper presents an updated Taxa-PFTs-Biome scheme, based on 18 biomes, 30 Plant Functional Types (PFTs) and 590 pollen taxa from 1630 surface pollen sites in China. The biomization results reveal a total of 16 biome types comprising eight new biomes. By comparing the simulated biome types with modern potential vegetation, 80% of the sampling sites were correctly assigned, which is considerably more accurate than studies which have used previous Chinese biomization schemes. The biome reconstruction for the mid-Holocene (6 ± 0.5 14C kyr B.P.) shows that: (1) In eastern China, tropical, subtropical, warm-temperate and cool-temperate forests did not significantly expand northward, whilst cold-temperate forests were absent from northeastern China; and (2) in central China, the western boundary of steppe vegetation was shifted westwards due to a ~150–300 km extension of the forest and forest-steppe biomes, which is close to the present-day 200–300 mm isohyet. The northwestward shift of the forest and forest-steppe in central China during the mid-Holocene indicates that moisture levels were enhanced compared to the present day. The climatic mechanism responsible was likely a strengthened East Asian summer monsoon, which resulted in increased moisture transport from the ocean to the semiarid regions in northern China, promoting the development of forest and forest-steppe vegetation. • An updated taxa-PFTs-Biome scheme, based on 1630 surface pollen sites in China, was established. • The average accuracy of the updated scheme is more than 80%, which higher than previous Chinese schemes. • The boundary of the forest-steppe zone during mid-Holocene generally advanced northwestwards by about 200-300 km. [ABSTRACT FROM AUTHOR]

Little is known about the climate and environmental changes that have occurred in the extremely arid regions of China since MIS (Marine Isotope Stage) 3 (59–29 cal kyr BP), when most regions in northwestern China and the Tibetan Plateau featured warm and humid conditions. In this paper, we present a record of the climate changes in the Qaidam Basin in arid northwestern China over the past 40 kyr based on the mineralogy of a 35-m-long sediment core recovered from Qarhan Salt Lake. Our results show that the lake was a saline or hyper-saline lake saturated with respect to gypsum between 40 and 33 cal kyr BP. Beginning at 33 cal kyr BP, evaporite formation was dominated by halite precipitation, indicating that the lake salinity had increased extensively and that the climate became drier during 33–24.5 cal kyr BP. The lake salinity then increased continuously, resulting in the appearance of bischofite between 24.5 and 14.6 cal kyr BP. The disappearance of bischofite and the increase in gypsum indicate that the salinity of the water decreased slightly between 14.6 and 8.3cal kyr BP. However, during the last 8300 years, the lake has dried up and is now a playa. Generally, the climate was wet in late MIS 3, arid in MIS 2 (29–11.7 cal kyr BP), and hyperarid in the Holocene. The relatively humid conditions may have resulted from weak evaporation caused by the relatively low insolation and intense ice-albedo feedback in late MIS 3. The decreased insolation and dramatically increased Eurasian ice volume in MIS 2 may have led to limited precipitation, which resulted in persistent dry climate conditions in the Qaidam Basin. In the Holocene, the reduction in ice volume reduced the albedo, and this change, in conjunction with increased insolation, may have led to evaporation exceeding local precipitation, resulting in hyperarid climate conditions in the Qaidam Basin. • Climate change since late MIS 3 was studied in an extremely arid region of China. • The climate was wet in late MIS 3 but hyper-arid in the Holocene. • Northern Hemisphere insolation and Eurasian ice volume were the forcing mechanisms. [ABSTRACT FROM AUTHOR]

Since the Industrial Revolution, greenhouse gas emissions have caused global temperatures to rise gradually. The Paris Agreement aims to limit the global mean surface temperature increase to less than 2.0 °C relative to pre-industrial levels. China's land area accounts for ∼7% of the global land (65Ñ59S) area, and the arid area of China accounts for 12.41% of the total global arid area. Therefore, the degree of aridification/humidification in China is of great significance to climate change in China and the world. This paper evaluates the regional changes of drylands and humid lands in China based on the 1.5 °C and 2.0 °C increase targets for global mean surface warming(GMSW). We find a suitable warming target for China's climate from the perspective of aridification. The results show the following: 1) If the global mean surface temperature rises by 1.5 °C and 2.0 °C above pre-industrial levels, the mean surface temperature in China will increase by 2.0 °C and 2.8 °C, respectively. 2) Under the two GMSW targets, the degree of drought in some extremely arid areas in China was projected to decrease, which means that these areas may gradually be suitable for human habitation. 3) Regardless of which global surface temperature target is maintained, the humid lands in China will bear greater risks from warming than the drylands. Under these circumstances, the 1.5 °Ctargetwill lead to better outcomes for China than the 2.0 °C target. • The degree of drought in some extremely arid areas in China has decreased under global warming targets. • Humid lands in China will bear greater warming risks than the dry lands. • Global warming limited within 1.5 °C target for will lead to better outcomes for China than the 2.0 °C. [ABSTRACT FROM AUTHOR]

• Replenishment activities significantly impact lake evolution. • We highlight the contributions of groundwater and chemical reactions in lake salinity reduction. • Virtual sample is introduced in NETPATH hydrogeochemical model for lake. • High quality and large volume replenishment water will help rehabilitate lake ecosystem. • Results could be useful to promote sustainable lake water management in arid areas. Lakes in arid regions are ecologically valuable yet highly fragile due to intense evaporation. To provide an extra water supply for maintaining water balance in lakes, the Ecological Replenishment Water Program (ERWP) in northwest China has significantly changed the hydrological and hydrochemical conditions for these lakes. Descriptive statistics and water and mass balances, together with hydrogeochemical modeling were used in this study to gain an understanding of the impacts of water replenishment (irrigation and drainage water) on evolution for Shahu Lake. A virtual sample was introduced in NETPATH hydrogeochemical modeling to compute the net chemical reactions in the lake water. Variations in TDS indicated that the lake evolved to be saline during 2004–2012 (stage I) and then tended to be fresh during 2013–2014 (stage II). Results highlighted that groundwater outflow and chemical reactions were the overriding factors controlling chemical evolution in the lake system, which greatly depend on the replenishment activities. The salinity reduction from the virtual samples to the final samples were attributed to the precipitation of calcite and dolomite, dissolution of gypsum, Na-K and Na-Ca exchange, and the CO 2 degassing in the lake system at an annual scale of 0.11 g/L in stage I and 0.15 g/L in stage II. The quality of replenishment water was as important as quantity for rehabilitating lakes, as it significantly determines the occurrence of chemical reactions in lake water. Findings from this paper can provide insight into the evolution of arid lakes in response to replenishment activities and can help contribute to better management of a valuable and fragile resource. [ABSTRACT FROM AUTHOR]

Optimization of the urban landscape composition and configuration through initiative planning is important to sustainable development of the drylands of northern China (DNC). Taking the agro-pastoral transitional zone of northern China (APTZNC) as an example, this paper developed an approach of sustainable urban landscape planning (SULP) under the stress of climate change in the DNC. First, we quantify the amount of water resources under the future climate change impacts (CCI). Then, we adjust the urban land area based on water resources carrying capacity constraints. Finally, we use the LUSD-urban (Land Use Scenario Dynamics-urban) model to adjust the configuration of the urban landscape to avoid occupying important natural habitats and corridors, prime croplands, and floodplains. We find that the SULP can effectively mitigate the comprehensive effects of regional urban landscape dynamics on water resources, food security, ecological security, and flood risks. By performing the SULP, prime croplands, floodplains, and important natural habitats and corridors occupied by urban land will decrease by 2,187 km2, 750 km2, and 130 km2, respectively, during the period of 2015–2050 in the APTZNC. We also find that the proposed approach can effectively manage the impacts of climate change on water resource capacity and reduce water stress of the entire APTZNC and its sub-regions. Thus, the proposed SULP approach and the experiences from the case study in the APTZNC are helpful for guiding urban landscape planning to achieve sustainable development of cities in the DNC and even in the drylands around the world. • Sustainable urban landscape planning under the stress of climate change was performed. • Urban land area was adjusted based on water resources carrying capacity constraints. • Urban landscape configuration was adjusted to avoid occupying important areas. • The planning can mitigate the comprehensive effects of urban landscape dynamics. • Addressing the climate change impacts should be incorporated into urban landscape planning. [ABSTRACT FROM AUTHOR]

• Present a watershed pollution load model (HIMS–PL model) for semiarid and semihumid areas. • Analyze the sensitivity of HIMS–PL model. • Check the suitability of HIMS–PL model for simulations of streamflow, sediment and pollution load in semiarid and semihumid catchments. Modeling pollutant processes in soil and water is helpful to better understand a pollutant's potential adverse impacts on an environmental system. There are many watershed pollution load models; however, their effectivity is generally poor in semiarid and semihumid areas because of the complexity of hydrological processes and pollutant transport processes. In this paper, a pollution load module was combined with the well-established HIMS (Hydro-Informatic Modelling System) model for the purpose of simulating the processes of pollution generation and transport and quantifying the pollution load in semiarid and semihumid areas. The model has the advantages of a simple structure and low data requirement, and can simulate dissolved and solid-phase nitrogen and phosphorus. As a demonstration, the HIMS-pollution load (HIMS-PL) model was respectively tested for three semiarid and semihumid basins in China—the Liuhe and the Yixunhe River basins, two sub-basins of the Luanhe River basin, and the Chaohe River basin. Model simulations of streamflow and pollution loads at monthly time step accurately matched the observed streamflow (with NSEs 0.77–0.95 and REs 0.53–11.24%) and pollution load (with NSEs 0.54–0.83 and REs 2.45–12.72% for total nitrogen loads and with NSEs 0.51–0.79 and REs 2.22–19.70% for total phosphorus loads). In comparison with HSPF and GWLF models, the HIMS-PL model performed better than the GWLF model in all of the above-mentioned basins and better than the HSPF model in some of the basins. Overall, the proposed model is generally suitable for simulating streamflow and pollution load in semiarid and semihumid regions. [ABSTRACT FROM AUTHOR]