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The arid endorheic basin of northwest China is characterized by rich land resources, water shortage, and a fragile ecological environment. The establishment of a credible coupling model of groundwater and surface water based on multi-source observation data is an effective means to study the change in basin water cycles and the sustainable utilization of water resources in the past and future. Based on the latest understanding of hydrogeological conditions, hydrology and water resource utilization data in the middle reaches of the Heihe River Basin (HRB), this paper constructs an up-to-date coupling model of surface water and groundwater to study the water balance change of the basin. The water resources data series under historical replay and CMIP5 climate model prediction are constructed to predict future changes in water resources. The study shows that, under the joint influence of natural conditions and human activities, the average annual recharge of groundwater in the study area from 1990 to 2020 is 17.98 × 108 m3/a, the average annual discharge is 18.62 × 108 m3/a, and the difference between recharge and discharge is −0.64 × 108 m3/a. The total groundwater storage is −19.99 × 108 m3, of which the groundwater storage from 1990 to 2001 was −17.52 × 108 m3 and from 2002 to 2020 was −2.47 × 108 m3. Abundant water from 2002 to 2020 in the basin significantly improved the loss of groundwater storage. Under the prediction of historical reappearance and the CMIP5 CNRM-CM5 model RCP4.5 and RCP8.5 pathways, the groundwater level of the Heihe River–Liyuanhe River inclined plain falls first because the HRB has just experienced a wet season and then rises according to future climate change. The groundwater level of the inclined plain east of the Heihe River and Yanchi basin decreases continuously because of the change in water cycle caused by human activities. The erosion accumulation plain is located in the groundwater discharge zone, and the water level is basically stable. Under the conditions of water resource development and utilization, the runoff of Zhengyixia hydrological station cannot meet the requirements of the "97 Water Dividing Plan" of the State Council in most years in the future, and the ecological and production water in the lower reaches of HRB cannot be effectively guaranteed. With the implementation of water-saving irrigation under the RCP4.5 and RCP8.5 scenarios, the runoff of Zhengyixia can meet the "97 Water Diversion Plan". It is suggested to further improve the level of agricultural water savings in the middle reaches of the HRB and control the reasonable scale of cultivated land in order to reduce water consumption in the middle reaches of the HRB and implement sustainable utilization of water resources in the HRB. [ABSTRACT FROM AUTHOR]

Groundwater exploitations in semi‐arid regions result in significant declines of groundwater levels and streamflow and even trigger seasonal streamflow drying up, which may bring adverse impacts on riparian ecosystems. It is critical to explore future streamflow changes caused by variable climate scenarios and groundwater exploitation intensities; however, a comprehensive assessment of the streamflow drying up frequency remains lacking. Furthermore, the thresholds of controlling factors beyond which streamflow drying up occurs have rarely been explored. Here we develop an integrated surface water‐groundwater model for the Taoer River Basin (TRB), a typical semi‐arid watershed in northeast China. We apply the model to multiple future scenarios to reveal the frequency of potential streamflow drying up and explore the thresholds of controlling factors of streamflow drying up based on a decision tree method. We find that the groundwater level in the lower region of the TRB (LTRB) is hard to recover to the riverbed elevation and the streamflow drying up frequency is still high unless the groundwater exploitation is reduced by 50%. However, this leads to a competition between the ecological and economic objectives. Our results also show that the streamflow drying up frequency in the LTRB is very sensitive to the upstream water inflow that can be regulated through the reservoir operation or inter‐basin water diversion, indicating the importance of a basin scale strategic management. The findings of this paper can help policy makers sustainably exploit water resources in semi‐arid regions. [ABSTRACT FROM AUTHOR]

Groundwater is a primary freshwater resource for human consumption and an essential source for industry and agriculture. Therefore, understanding its spatial and temporal trends and drivers is crucial for governments to take appropriate measures to manage water resources. This paper uses Gravity Recovery and Climate Experiment (GRACE) satellite data and the Global Land Data Assimilation System (GLDAS) to derive groundwater storage anomalies (GWSAs) and to analyze the spatial and temporal trends of GWSA in different regions of China (Xinjiang, Tibet, Inner Mongolia, North China Plain, South China, and Northeast China). It used groundwater-level observation data to verify the accuracy of GWSA estimates and analyzed the drivers of regional GWSA changes. The results showed that: (1) GWSA in South China increased at a rate of 4.79 mm/a from 2003 to 2016, and GWSA in other regions in China showed a decreasing trend. Among them, the decline rates of GWSA in Xinjiang, Tibet, Inner Mongolia, North China Plain, and Northeast China were −6.24 mm/a, −3.33 mm/a, −3.17 mm/a, −7.35 mm/a, and −0.75 mm/a, respectively. (2) The accuracy of the annual-scale GWSA estimates was improved after deducting gravity losses due to raw coal quality, and the correlation coefficient between GWSA and groundwater levels monitored by observation wells increased. (3) In Xinjiang, the annual water consumed by raw coal mining, industrial, and agricultural activities had a greater impact on GWSA than rainfall and temperature, so these human activities might be the main drivers of the continued GWSA decline in Xinjiang. Water consumption by raw coal mining and industry might be the main drivers of the continued decline in GWSA in Inner Mongolia and the North China Plain. The increase in groundwater storage in South China was mainly due to the recharge of rainfall. [ABSTRACT FROM AUTHOR]

Water system management is a worldwide challenge, especially in arid and semi-arid regions. Ecological water conveyance projects aim to raise the groundwater table, thereby saving natural vegetation and curbing ecological deterioration. Since 2000, these projects have been implemented in the arid zone of northwest China, with generally successful outcomes. Taking a portion of the lower reaches of the Tarim River as the study area, this paper analyzes in detail the ecohydrological effects which have occurred since the launching of artificial water conveyance 20 years ago. The results show that the groundwater table in the upper, middle and lower segments of the Tarim River's lower reaches has been raised on average 4.06, 4.83 and 5.13 m, respectively, while the area of surface water bodies connected to those sections has expanded from 49.00 km2 to 498.54 km2. At the same time, Taitema Lake, which is the terminal lake of the Tarim River, has been revived and now boasts a water area of 455.27 km2. Other findings indicate that the surface ecological response is extremely sensitive and that the area of natural vegetation has expanded to 1423 km2. Furthermore, the vegetation coverage, vegetation index (NDVI), and Net Primary Productivity (NPP) have increased by 132 km2, 0.07 and 7.6 g C m−2, respectively, and the Simpson dominance, McIntosh evenness, and Margalef richness indices have risen by 0.33, 0.35 and 0.49, respectively, in the monitored sample sites. As well, the carbon sink area has expanded from 1.54% to 7.8%. Given the increasing intensity of the occurrence of extreme hydrological events and successive dry years, similar ecological water conveyance projects should be considered elsewhere in China and in other parts of the world. The water conveyance scheme has generally proven successful and should be optimized to enhance the benefits of ecological water conveyance under water resource constraints. [ABSTRACT FROM AUTHOR]

An accurate understanding of the relationship between reservoir construction and the dynamic change of groundwater level in downstream areas is of great significance for rational development and utilization of water resources. At present, the research on the interaction between surface water (SW) and groundwater (GW) mainly focuses on the interaction between river and GW. There are few studies on the impact of the reservoir construction on GW level in downstream loess irrigation area. Rainfall, evaporation and climate temperature have a great impact on W level, but the impact of reservoir construction on the GW level should not be ignored in the utilization of water resources. In this paper, a GW flow model under a natural boundary was established by numerical simulation. Taking Heihe Jinpen Reservoir in Heihe River watershed as the research object, the influence of the construction of a mountain reservoir on the dynamic change of GW level in the downstream loess region is studied. By comparing the GW level under the natural state without reservoir construction and the measured GW level after the reservoir was built, the variation of the GW depth in the loess area of the lower reaches in the Heihe River watershed is obtained. The results show that simulation accuracy of the interaction between SW and GW was reasonable; after the Heihe Jinpen Reservoir construction, the mean GW level decrease was about 6.05 m in the downstream loess irrigation area in Guanzhong Basin. It provides a method for the simulation and prediction of SW–GW conversion laws. This study is also of great significance to explore the change law of the water cycle and improve the utilization rate of water resources. [ABSTRACT FROM AUTHOR]

In the paper, we analyze the climate-related risks of rainstorm floods, droughts and water shortages, high temperatures, and heavy hazes in the Xiongan New Area. A warming and drying trend was seen in Xiongan New Area during 1961–2018, as evidenced by the increase in the number of high-temperature days and the maximum rainfall intensity per hour, a decrease in surface water resources and groundwater levels, a reduction in wind speeds, and weakening of the self-purification capacity of the atmosphere. It is estimated that the areas at high risk of floods and heats will increase by 15.7 and 15.6% in around 2035 relative to 1986–2005, respectively. Although the runoff in the Daqing River Basin will increase, the construction of Xiongan New Area means that the imbalance between the supply and demand of water resources will remain. Climate change adaptation measures should therefore be improved in the planning and construction of Xiongan New Area. Finally, we discuss the approaches to address climate-related risks in this new area. [ABSTRACT FROM AUTHOR]

Rapid population growth is increasing pressure on the world water resources. Agriculture will require crops to be grown with less water. This is especially the case for the closed Yellow River basin, necessitating a better understanding of the fate of irrigation water in the soil. In this paper, we report on a field experiment and develop a physically based model for the shallow groundwater in the Hetao irrigation district in Inner Mongolia, in the arid middle reaches of the Yellow River. Unlike other approaches, this model recognizes that field capacity is reached when the matric potential is equal to the height above the groundwater table and not by a limiting soil conductivity. The field experiment was carried out in 2016 and 2017. Daily moisture contents at five depths in the top 90 cm and groundwater table depths were measured in two fields with a corn crop. The data collected were used for model calibration and validation. The calibration and validation results show that the model-simulated soil moisture and groundwater depth fitted well. The model can be used in areas with shallow groundwater to optimize irrigation water use and minimize tailwater losses. [ABSTRACT FROM AUTHOR]

Jinci Spring is one of the most famous karst spring in Northern China and is the main drinking and irrigation water source of Taiyuan city, Shanxi Province. It has special significance in terms of humanities and water resources. Because of the continuous over-exploitation of groundwater, the water level of groundwater has been decreased significantly. The flow of Jinci Spring has decreased year by year since the 1970s, and in 1994 it cut off completely. The flow cutoff has brought huge losses to the local economy and negatively impacted the ecological environment. From the hydrogeological conditions of Jinci Spring area to study, the dynamic change in karst groundwater level will provide a basis for the protection and rational exploitation of karst water in the spring area. The previous research on Jinci Spring area was limited to the spring flow and water level changes, lack of analysis to the overall spring area and the decay process of spring flow. This paper takes the overall spring area as research object. According to groundwater level data over 1961–2012, the period is divided into two phases of decline and recovery. Human activities in the region and corresponding groundwater evolution at various stages were systematically analyzed, and the reservoir capacity was calculated for each period of decline. The results show that the average reservoir capacity decreased from 920 (1954–1960) to 116 (1961–1977) to 31 (1978–1994) million m3. The important effect of "Water Resumption" project on groundwater in the area during the remediation period was also analyzed. In the light of observed increases in groundwater level during this stage, the project has a notably positive effect. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Fluvial-eolian systems were identified in the Late Jurassic Tianchihe Formation. • The associations of eolian dune and eolian sandsheet indicate dry eolian system. • An evolving erg system occurred in the upper part of the Tianchihe Formation. • The vertical transition from fluvial to eolian systems suggest a drying trend. • The uplift of the East China Plateau resulted in the erg development. Abstract Eolian systems were widespread in China in the Cretaceous. However, the reports of pre-Cretaceous eolian and its related systems are scarce, which prohibits studying the construction, accumulation and preservation of eolian systems as well as its allogenic and autogenic controlling factors. In this paper, we report on fluvial–eolian successions from the Late Jurassic Tianchihe Formation in the Ningwu–Jingle Basin. These successions represent the oldest reported inland fluvial–eolian systems in China. Fourteen lithofacies types are recognized in the Tianchihe Formation and have been grouped into six facies associations, including meandering fluvial channel, levee and overbank in the lower part, and eolian sandsheet, eolian dune, ephemeral fluvial channel and floodplain in the upper part. The fluvial system comprises a series of wetting upward cycles, which indicate humid climate culminating in high precipitation and shallow water table level. Eolian dune deposits composed of grainflow, grainfall, wind ripple strata and pin stripe laminations currently implies that all deposits types are internally bounded by reactivation surface and superimposition surface, suggesting compound dunes or draas. Eolian sandsheet deposits consist dominantly of subcritical climbing translatent strata and pin stripe lamination. The association of eolian dune and eolian sandsheet is development of a dry eolian system. Twelve drying upward cycles mainly composed of eolian sandsheet–eolian dune successions and four wetting upward cycles consisting of eolian sandsheet/dune–ephemeral fluvial channel/floodplain successions occur in the eolian system. These repeated cycles likely reflect an evolving erg system directly controlled by sediment supply, sediment availability and relative water table. The vertical transition from fluvial to eolian systems indicate a local climatic oscillation from relatively humid to arid conditions, which may be related with the uplift of the East China Plateau in the Late Jurassic. [ABSTRACT FROM AUTHOR]

As the largest irrigation area in northwest China, the middle and lower reaches of the Yarkant River basin are limited in economic development by the shortage of surface water resources and the increasing demand for groundwater resources from agriculture and industry, and the phenomenon of over-exploitation is becoming increasingly serious, which is not in line with the concept of sustainable development. Therefore, improving the efficiency of water resource utilization while curbing the trend of declining groundwater levels is an important issue that needs to be addressed in the middle and lower reaches of Yarkant at present, specifically, by establishing a distributed hydrological model MIKE SHE based on a soil texture dataset. The model efficiency coefficient Ens, the water balance coefficient (WB), the correlation coefficient r, and the relative error Re were selected to evaluate the model's applicability. The results were: Ens = 0.84, WB = 0.80, and r = 0.96 for the annual scale runoff simulation and Ens = 0.85, RE = 0.61, and r = 0.96 for the monthly scale runoff simulation. The relative errors between the simulated and observed values of the typical observation wells were 3.45%, 1.59%, 2.52%, and 0.35%. According to the analysis of the soil parameters on the runoff sensitivity and groundwater table sensitivity, the saturated hydraulic conductivity had the greatest effect on the peak discharge. The results show that the MIKE SHE model has some applicability in the lower and middle reaches of the Yarkant River basin. [ABSTRACT FROM AUTHOR]

The salinity of groundwater in Qinzhou Bay has been increasing since 2013. This phenomenon affects livelihoods and the local agricultural economy, specifically in the Longmengang area. In this work, we investigate the causes of water salinization to provide evidence for effectively managing the local water resources and improving water quality. We collected 110 samples of water from spatially distributed local wells, rivers, reservoirs, and the sea, and conducted a hydrochemical study complemented by numerical modeling. We found that water pumping and mariculture practices are the principal contributors to seawater intrusion into the groundwater table, which leads to increased water salinization. Plain Language Summary: Groundwater salinity in Qinzhou Bay is increasing due to excessive well water extraction and mariculture practices, which promote seawater intrusion into the local groundwater table. Based on the hydrochemical analyses, the spatially distributed trend of ions content in groundwater shows low concentrations inland and increasing concentrations seaward. However, several localities of Qinzhou Bay are out of this scenario because of artificial activities requiring specific monitoring and regulation. Key Points: Field investigations and hydrochemical analyses show salinization of groundwater in Qinzhou BayHydrogeological modeling indicates that different processes contribute to water salinizationGroundwater salinization in Longmen Island is caused by excessive groundwater use and mariculture practices [ABSTRACT FROM AUTHOR]

Enrichment mechanisms of high‐arsenic (>10 μg/L) groundwater in confined aquifers with sand‐gravel sediments were rarely documented. Both groundwater and sediment were sampled to investigate mechanisms of groundwater arsenic mobility in sand‐gravel confined aquifers from the Songnen Basin, China. The results show that, although high arsenic groundwater was present in both shallow sandy (<60 m) and deep sand‐gravel aquifers (60–100 m), relatively higher arsenic groundwater was hosted in the deep confined aquifers. The significantly higher proportion of biologically degradable organic carbon (BDOC) in deep confined groundwater than those in shallow unconfined ones (p = 0.03) suggests that higher arsenic concentrations were associated with higher DOM biodegradability. High‐arsenic groundwater was the result of Fe(III) oxide reduction facilitated by BDOC degradation. Arsenic‐rich pyrite framboids were observed in shallow aquifers, which would lower groundwater arsenic concentrations. Sand‐gravel sediments in deep aquifers had remarkably higher contents of extracted Fe(III) oxides and the bound arsenic, HCl‐extractable Fe(II) minerals, and adsorbed arsenic, but considerably lower contents of Mn oxides and Mn(II) minerals than the shallow sandy sediments. Siderite, which is not as efficient as pyrite in sequestering arsenic, was the dominant Fe(II) mineral in the deep aquifer. In the deep aquifer, Mn oxide reduction was almost completed and Fe(III) oxide reduction was predominated, which resulted in high concentrations of groundwater arsenic due to high arsenic/iron molar ratio in the Fe(III) oxides. This study proposed that geogenic high‐arsenic groundwater can occur in sand‐gravel aquifers being high in Fe(III) oxide‐bound arsenic but poor in Mn oxides under reducing conditions. Plain Language Summary: Deep aquifers being mainly composed of sand‐gravel sediments were generally believed to host "safe" drinking water resources. Recently, high arsenic groundwater has frequently been observed in those deep aquifers isolated from shallow groundwater by clay aquitard. However, mechanisms of groundwater arsenic enrichment in those deep aquifers are poorly understood. This comprehensive study shows that arsenic was in situ mobilized from microbially driven reduction of arsenic‐bearing Fe(III) oxides in the deep aquifer with higher proportion of degradable organic carbon to DOC, higher contents of Fe(III) oxide‐bound arsenic and adsorbed arsenic, and lower contents of Mn oxides in the deep aquifer relative to those in the shallow one. The Fe(III) oxide‐bound and adsorbed arsenic were the most reactive mobile phases in deep aquifer sediments with low contents of Mn oxides under reducing environments. Our findings emphasize that the contents of Fe(III) oxide‐bound arsenic and Mn oxides in aquifer sediments were key factors controlling groundwater arsenic enrichment. Key Points: Elevated groundwater arsenic (As) concentration in both shallow sandy and deep sand‐gravel aquifers were caused by Fe(III) oxide reductionPyrite precipitation lowered shallow groundwater As level, while higher As level occurred in deep aquifers with siderite precipitateHigh‐As groundwater occurred in sand‐gravel aquifers with high contents of Fe(III)‐oxide bound As and negligible Mn oxides [ABSTRACT FROM AUTHOR]

The well-known White method (A method of estimating ground-water supplies based on discharge by plants and evaporation from soil: Results of investigation in Escalante Valley, Utah. Washington D.C, US Geological Survey. Water Supply Paper 659-A United States Department of the Interior, 1932) based on diurnal water table observations has been widely applied to estimate groundwater evapotranspiration (ETG) from phreatophyte vegetation. One of the limitations of this method is its large uncertainties in quantifying the daily groundwater recovery rate (r), which is assumed to be equal to the average rate of groundwater level rise between midnight (i.e., 00:00 h) and 04:00 h. Recent studies pointed out that ETG is highly dependent on the shape and duration of the diurnal clear-sky solar radiation curve and that using the groundwater recovery rate over a short interval of nighttime hours to represent the daily r may lead to large uncertainties in ETG estimates. In this study, we analysed the dependence of the estimated daily r on the sunset and sunrise timings. Numerical experiment results showed that the estimated r is highly sensitive to the duration between sunset and sunrise, which varies seasonally. Instead of using fixed time spans (TSs), e.g., from midnight to 04:00 h, we recommend a more universal method for determining the TS, which is associated with the sunset and/or sunrise timings and used to estimate the daily r. This dynamic TS approach was tested at a Tamarix ramosissima-dominated riparian site with a hyper-arid climate (precipitation of 35 mm a−1) in northwestern China. Compared with the observed evapotranspiration (ET), our approach showed better performance and less subjectivity in estimating ETG than the traditional White approach. [ABSTRACT FROM AUTHOR]

• The mean groundwater table depth in China dropped by approximately 0.2 m (P < 0.01) during 1979–2018. • The Noah-MP land model forced with reanalysis climate data can reasonably capture terrestrial water and radiation processes across China. • Incorporating the groundwater lateral flow process enhances the seasonality of modeled terrestrial water and radiation processes on a regional scale. Faced with intensified climate change and ever-increasing water demand, the groundwater table depth is vital to sustaining terrestrial environments in a country such as China; however, on a regional scale, insufficient research has been conducted on its variability thus far. Using a land model forced with reanalysis climate data, this paper investigates groundwater table depth changes across China for the 1979–2018 period. The results show a significant overall reduction in the groundwater table depth in China during the past 40 years without explicit consideration of direct human influence. There is an approximately 0.2 m decrease on average, but it is approximately 0.5 m in southern China and 0.8 m to the north of 35°N despite a 1.2 m rise in part of this region due to an increasingly wet climate and a topographic water convergence. The findings provide a first-order pattern of historical groundwater table responses to climate change, highlighting inherent links among subsurface-surface-atmosphere water cycles and worsened terrestrial water availability in China. A model evaluation compared with in situ observations has demonstrated the model's ability to realistically portray terrestrial water and energy balances on regional scales, as well as the enhancement of their seasonality with incorporated lateral groundwater flow processes. This ability gives us reasonable confidence in the simulated trends and spatial variability. Nonetheless, the mean groundwater table still shows large biases relative to observations, and the problems of human influence, two-way interactions between groundwater and surface water, and local topographical complexity have yet to be properly addressed in the present study and deserve further research. [ABSTRACT FROM AUTHOR]

The shelterbelt forest between oases and the desert plays a vital role in preventing aeolian disasters and desertification in arid regions of northwest China. Tamarix ramosissima (T. ramosissima), a typical perennial and native xerophyte shrub in Northwest China, grows naturally and is widely used in building artificial shelterbelt forests. The balance between water consumption and the availability of water determines the survival and growth of T. ramosissima. How T. ramosissima copes with extremely low rainfall and a deep groundwater table remains unknown. To answer this, the transpiration and the water sources of T. ramosissima were investigated by the heat balance and oxygen isotopic analysis method, respectively. Our results show that the daily T. ramosissima stem sap flow (SSF) was positively correlated with air temperature (Ta), photosynthetically active radiation (PAR), and the vapor pressure deficit (VPD). We found no significant relationship between the daily SSF and soil moisture in shallow (0–40 cm) and middle (40–160 cm) soil layers. Oxygen isotope results showed that T. ramosissima mainly sources (>90%) water from deep soil moisture (160–400 cm) and groundwater (910 cm). Diurnally, T. ramosissima SSF showed a hysteresis response to variations in PAR, Ta, and VPD, which suggests that transpiration suffers increasingly from water stress with increasing PAR, Ta, and VPD. Our results indicate that PAR, Ta, and VPD are the dominant factors that control T. ramosissima SSF, not precipitation and shallow soil moisture. Deep soil water and groundwater are the primary sources for T. ramosissima in this extremely water-limited environment. These results provide information that is essential for proper water resource management during vegetation restoration and ecological reafforestation in water-limited regions. [ABSTRACT FROM AUTHOR]

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Researching the watershed-scale spatiotemporal groundwater and surface water mixing function, groundwater recharge heights and age can provide important information to watershed water sources management and water pollution controlling. In this study, 20 groundwater samples, 6 precipitation samples, and 40 surface water samples in the Yiluo River watershed in middle China were collected, and the mixing function between groundwater and surface water, recharge height, and age of groundwater was studied by using hydrochemistry (Cl, DO, EC, pH), radioactive isotopes (14C), and stable isotopes (13C, 18O, 15N). The results showed that river and shallow groundwater had frequent interaction. Evaporation function played a major role in the groundwater recharging process. Groundwater age displayed spatial and seasonal variations, and the age ranged from 660 to 2800 years (dry season) and 560 to 1800 years (wet season) in downstream and midstream, while the age range from 12,025 to 143,600 years (dry season) and 10,560 to 12,650 years (wet season) in upstream. The average recharge height of downstream and midstream both in dry and wet seasons is about 576.00 to 908.70 m. While in upstream, both, in the dry and wet seasons, ranged from 1285 to 2680 m. The mixing function between groundwater and surface water displayed spatiotemporal variety. These results of this study can provide useful information for the watershed-scale water resources management. [ABSTRACT FROM AUTHOR]

Of all economic activities in the North China Plain, agriculture accounts for the highest consumption of water resources. As water saving by using technologies to alleviate groundwater depletion has its limitations, adjusting the cultivation patterns of water-intensive crops becomes an unavoidable measure to ensure water sustainability. Different cropping patterns (including fallowing) and water supply scenarios were set up, using the DSSAT crop model and a regression model, in order to predict the effects of cropping adjustments on groundwater sustainability and food production in the piedmont region of the plain. The results indicate that: (1) irrigation water requirement needs to be limited to a maximum level of 187 mm/a to sustain groundwater at the present level. Above this level, every 100 mm of irrigation pumping leads to a decline of 0.49 m in the groundwater level; (2) under the current water supply conditions, and taking groundwater sustainability, food supply, water use efficiency and soil fertility recovery into consideration, leaving 34% of the cropland fallow or leaving it fallow every 3 years seems to be the best option; (3) If an extra amount of water of 0.2 or 0.5 billion m3 is supplied as a result of the SNWT Project, the percentage of cropland which should be left fallow can decrease to 25% or 11% respectively. The comprehensive information on the water and food nexus derived from this study can provide a reference framework for policies concerning sustainable water use and food security in the region. [ABSTRACT FROM AUTHOR]

Diversification of vegetation communities could be associated with the change of groundwater depth (GD). To get a better understanding of this relationship, a field survey assessing GD, and herbaceous plants etc. was carried in Tongliao plain (TP), northwestern China, where GD has declined significantly mainly due to pumping for agricultural irrigation. The photos data method was used to identify vegetation characteristics including coverage, biomass, height, ecological type, and name etc. Some diversity indexes were applied to identify the relationship between the groundwater table and the plant features. Growth and composition of vegetation were affected by the depth of groundwater and the degree of utilization of herbaceous vegetation on water resources. Different depth of groundwater had different influence on vegetation. The ecotype distribution of vegetation following depth based on survey data demonstrated that mesophytes, mesoxerophytes and xerophytes were found over groundwater depths between 1.38 and 3.43 m, 1.4 and 3.4 m and 2.4 and > 4.0 m respectively. This study proved that the depth of 3.4 m may be the transition range for the evolution of vegetation in TP. [ABSTRACT FROM AUTHOR]

Human activities and climate change are two key factors influencing the variation of the total amount of available surface and groundwater, hereafter termed water resources. Quantitatively separating their impacts remains a challenge. To this end, we used time-varying Budyko-type equations and a hierarchical Bayesian model in this paper to separate their impacts in 31 provincial-level divisions of China. The time-varying Budyko-type equations treat the Budyko equation parameter w as a variable, which depends on human activities (represented by per capita gross regional production) and climate change (represented by temperature and precipitation). The hierarchical model quantifies the uncertainty of parameters and the interrelation between covariates across regions in China. The results show that the time-varying Budyko-type equation can improve the fitting capability for water resources in China. The hierarchical Bayesian model, which considered spatial dependence, reduced the uncertainty of the parameters compared to spatially independent counterparts. For most regions of China, human activities reduce water resources while climate change increases them. Southeastern China is the most influenced area, and its water resources decreased approximately 50 mm because of human activities. This study can provide a basis for water resource management under climate change and human activity constraints in China. [ABSTRACT FROM AUTHOR]

Managed aquifer recharge operations are often conducted in near-bank areas to regulate water resources or reduce seawater intrusion. Yet little is known about the influence of surface water level fluctuations at different temporal scales on MAR performance. A generalized conceptual model was developed based on an investigation site in Western China as a basis to simulate the response surface water level fluctuations on the water table, artificially recharged water lens (formed by the artificially recharged water), groundwater flow paths and average travel times (which is an important control on how quickly contaminants are flushed out of aquifers), and the discharge of the artificially recharged aquifer during the surface water level fluctuation. The results showed a fluctuating groundwater table in the artificially recharged near-bank aquifer under the influence of surface water level fluctuations. The peak values of the increment of the groundwater table induced by artificial recharge decreased with the increase of the period and amplitude of surface water level fluctuation, but the trough values of the increment of water table increases with that. The penetration depth of surface water into the aquifer with a fluctuating surface water level leads to a decreasing increment of the groundwater table which follows a power law. The fluctuating surface water level leads to dynamic changes of artificially recharged water lens morphology and a thinner artificially recharged water lens. A mixing zone of recharged water and ambient water could be found in the artificially recharged near-bank area, which is expected to lead to modifications in the geochemical conditions in the artificially recharged near-bank aquifer. A longer period of surface water level fluctuation leads to a longer average travel time, but the larger penetration depth of surface water and amplitude lead to a shorter average travel time. The peak discharge of the near-bank aquifer was found to decrease with the period of surface water level fluctuation, but it increases with penetration depth and amplitude. This study is important in providing insights into the performance of near-bank managed aquifer recharge with respect to surface water level fluctuation. [ABSTRACT FROM AUTHOR]

In recent decades, strong human activities have not only brought about climate change including both global warming and shifts in the weather patterns but have also caused anomalous variations of hydrological elements in different basins all around the world. Studying the mechanisms and causes of these hydrological variations scientifically is the basis for the management of water resources and the implementation of ecological protection. Therefore, taking the Yongding River mountain area as a representative watershed in China, the changes of different observed and simulated hydro-meteorological variables and their possible causes are analyzed on an inter-annual scale based on ground based observations and remotely sensed data of hydrology, meteorology and underlying surface characteristics from 1956 to 2016. The results show that the annual natural runoff of Guanting hydrological station in the main stream of the Yongding River, Cetian hydrological station and Xiangshuibao hydrological station in the tributary of the Yongding River all have a significant decreasing trend and abrupt changes, and all the abrupt change points of the annual natural runoff series of the three hydrological stations appear in the early 1980s. On the inter-annual scale, the water balance model with double parameters is unable to effectively simulate the natural surface runoff after the abrupt change points. The annual average precipitation after the abrupt change points decreases by no more than 10%, compared with that before the abrupt change points. However, the precipitation from July to August, which is the main runoff-production period, decreases by more than 25%, besides the intra-annual temporal distribution of precipitation becoming uniform and a significant decrease in effective rainfall, which is the source of the runoff. Meanwhile, the NDVI in the basin show an increasing trend, while the groundwater level and land water storage decrease significantly. These factors do not lead only to the continuous reduction of the annual natural runoff in the Yongding River mountain area from 1956 to 2016, but also result in significant changes of the hydro-meteorological relationship in the basin. [ABSTRACT FROM AUTHOR]

Precise multi-time scales prediction of groundwater level is essential for water resources planning and management. However, credible and reliable predicting results are hard to achieve even to extensively applied artificial intelligence (AI) models considering the uncontrollable error, indefinite inputs and unneglectable uncertainty during the modelling process. The AI model ensembled with the data pretreatment technique, the input selection method, or uncertainty analysis has been successfully used to tackle this issue, whereas studies about the comprehensive deterministic and uncertainty analysis of hybrid models in groundwater level forecast are rarely reported. In this study, a novel hybrid predictive model combining the variational mode decomposition (VMD) data pretreatment technique, Boruta input selection method, bootstrap based uncertainty analysis, and the extreme learning machine (ELM) model named VBELM was developed for 1-, 2- and 3-month ahead groundwater level prediction in a typical arid oasis area of northwestern China. The historical observed monthly groundwater level, precipitation and temperature data were used as inputs to train and test the model. Specifically, the VMD was used to decompose all the input-outputs into a set of intrinsic mode functions (IMFs), the Boruta method was applied to determine input variables, and the ELM was employed to forecast the value of each IMF. In order to ascertain the efficiency of the proposed VBELM model, the performance of the coupled model (VELM) hybridizing VMD with ELM algorithm and the single ELM model were estimated in comparison. The results indicate that the VBELM performed best, while the single ELM model performed the worst among the three models. Furthermore, the VBELM model presented lower uncertainty than the VELM model with more observed groundwater level values falling inside the confidence interval. In summary, the VBELM model demonstrated an excellent performance for both certainty and uncertainty analyses, and can serve as an effective tool for multi-scale groundwater level forecasting. [ABSTRACT FROM AUTHOR]

With rapid economic development, demand for water resources is continuously increasing, which has resulted in common overexploitation of groundwater, particularly in megacities. This overexploitation of groundwater over many years has brought a series of adverse problems, including groundwater level decline, land subsidence and hydrogeological issues. To quantitatively describe these risks, we propose a risk evaluation model for groundwater exploitation and utilization. By deducing and expanding on the cusp catastrophe type, this study breaks through the limitations on the catastrophe assessment method, e.g., the number of indicators, and establishes an improved catastrophe assessment model for groundwater exploitation and utilization risk. In addition, the index system of the risk evaluation is constructed including three criterion layers: groundwater system condition (B1), groundwater exploitation and utilization (B2) and groundwater environmental problems (B3) and is tested for the conditions in Shanghai City, eastern China. The evaluation results show that the comprehensive risk values for groundwater exploitation and utilization in all districts (counties) of Shanghai are between 0.68 and 0.85, which categorizes the city as in the moderate risk zone; therefore, the improved catastrophe model is suitable for assessing groundwater exploitation risk in Shanghai City and should be applicable more broadly for the effective protection and sustainable supply of groundwater. [ABSTRACT FROM AUTHOR]