Uncertainty in global groundwater storage estimates in a Total Groundwater Stress framework

Improving water efficiency is more effective in mitigating water stress than water transfer in Chinese cities

The interactions between human and natural systems and their effects have unforeseen results, particularly in the management of water resources. Using water stress mitigation as an example, a water resources management effect index (WRMEI) was created to quantitatively evaluate the trends of water management effects. This revealed that the WRMEI was decreasing due to the impact of the water resources management process. The findings demonstrate that water resources management has unintended effects: there was a gap between the expectation of water stress to be mitigated and the actual results of water stress increasing. That is caused by human activities in water utilization: (1) increasing available water resources from water transfer was not utilized sparingly in the receiving cities-increased water transfers from external sources increase domestic water consumption per capita; (2) improving water efficiency has a positive effect on mitigating water stress, but the population growth decreased the efficiency. It was concluded that much greater attention needs to be paid to water conservation in residential and living use to counter these unintended water management effects.

The catastrophic effects of groundwater intensive exploitation and Megadrought on aquifers in Central Chile: Global change impact projections in water resources based on groundwater balance modeling

Central Chile is undergoing its most severe drought since 2010, affecting ecosystems, water supply, agriculture, and industrial uses. The government's short-term measures, such as increasing groundwater extraction (by 383 % from 1997 to 2022), are exacerbating the situation, leading to long-term hydrological deterioration. The objective of this research is to establish the main processes driving the water table depth evolution within Central Chile over the period 1979-2023. This is done by conducting groundwater balances on five major hydrological basins of Central Chile. For the Megadrought (MD) period (2010-2022), the groundwater level depths reflect not only the recharge variability but, especially, the forcing trend of groundwater withdrawals: they represent 35 % and 65 %, respectively, of the total phreatic level drawdown. This result underlines the dominant role played by groundwater withdrawals in the current delicate state of Central Chile's groundwater resources, while revealing that drought is a new complex phenomenon to deal with, in the midterm, to revert the current water resource trend in Central Chile. Our study moreover presents the impact of climate change in the basin in the framework of six different groundwater withdrawal scenarios. In the worst case (i.e., RCP8.5), the aquifer recharge decreases 18 % with respect to 1979-1997, which is the period assumed to be unaffected by the impact of MD and withdrawals. Such a reduction may be irrelevant in the dynamics of the aquifer system if the current extraction rate does not change. The estimated recovery time needed to reach aquifer conditions equal to those of the unaffected period is approximately 50 years.

Hydrogeochemical properties of groundwater and associated human health hazards in coastal multiaquifers of India

Due to the scarcity of water supplies, coastal groundwater quality most importantly influences sustainable development in the coastal region. Rising groundwater pollution through heavy metal contamination is an intense health hazard and environmental concern worldwide. This study shows that 27%, 32%, and 10% of the total area come under the categories very high, high, and very low human health hazard index (HHHI) accordingly. This area's water quality is also much polluted; the study shows approximately 1% has very good water quality. High concentrations of Fe, As, TDS, Mg2+, Na, and Cl- are relatively noticed in the portion of the western part of this district. The concentration of heavy metals in coastal aquifers influences the groundwater pollution of that region. The average heavy metal concentration in this region is 0.20 mg/l (As) and 1.160 mg/l (TDS). The groundwater quality and hydrogeochemical properties are determined through the Piper diagram. The study stated that TDS, Cl- (mg/l), and Na+ (mg/l) are the most regulatory issues of vulnerability. In the present study region, a huge number of alkaline substances are present resulting in the water being unfit for drinking purposes. Lastly, it is clear from the study's findings that multiple risks exist there like As, TDS, Cl-, and other hydrochemical parameters in the groundwater. The proposed approach applied in this research work may be a pivotal tool for predicting groundwater vulnerability in other regions.

Change in groundwater table depth caused by natural change and human activities during the past 40 years in the Shiyang River Basin, northwest China

Groundwater is the primary water source for agriculture, social economy, and ecosystem in the Shiyang River Basin (SRB), northwest China. Research on its variation and attribution is of great importance for the sustainable development of local economy, water resources, and the environment. In this study, the changes in the groundwater table depth (GTD) during 1980-2017 in different sub-basins and different periods were analyzed using the linear trend and moving t-test methods. The contribution of natural and human activity to GTD in the before and after periods of the Comprehensive Treatment Program of the SRB (CTSRB) were quantified using a multiple general linear model. The results showed that (1) the GTD in SRB showed a significant increasing trend during 1980-2017, and it could be divided into three stages: slow increase (1980-1987), rapid increase (1987-2008), and spatially different trends (2009-2017). In sub-basins, the increasing rates in the three stages in Wuwei were 1.05 m/10a, 2.86 m/10a, and 4.50 m/10a, respectively, while those in Minqin were 3.89 m/10a, 6.24 m/10a, and 0.85 m/10a, respectively. (2) The contribution of human irrigation activity to GTD in Minqin decreased from 77.3 % during the pre-CTSRB period to 38.0 % during the post-CTSRB period, while that in Wuwei increased from 67.3 % to 83.8 %. This was due to the CTSRB focusing on the groundwater and ecological restoration in the lower reaches of SRB. (3) The dominant attributing factor to the increase in GTD was groundwater exploitation driven by expanded irrigated-farmland during the pre-CTSRB period. However, the implementation of CTSRB has achieved remarkable results, and the groundwater level in Minqin virtually reached a stable state, especially in the Lake irrigation district. This study provides a reference and basis for sustainable utilization and management of groundwater resources in similar arid and semi-arid regions.

The alarming state of Central Chile's groundwater resources: A paradigmatic case of a lasting overexploitation

Ensuring water supply under climate change scenarios is a global concern, and groundwater resources play a crucial role. Aquifer depletion is a worldwide trend, and Chile is no exception. Through a statistical approach with strong hydrogeological criteria, the groundwater overexploitation phenomenon is studied in Central Chile, the most populated region in this mountainous country. With this purpose, we assess the evolution of groundwater levels and pumping between 1970 and 2020 by analysing 26,065 groundwater rights and 222 observation wells. Withdrawals increased from 498 hm3 in 1970 to 8883 hm3 in 2020. We recognised two general trends in groundwater levels: a quasi-steady state hydrodynamic regime pre-1988 and sustained decline post-1988, exacerbated since 2010 with the start of the Megadrought. Although groundwater recharge is expected to decrease during this severe drought, the declining trend strongly correlates with pumping but not with precipitation changes. Climate forcing is usually invoked to warrant the dramatic depletion of groundwater resources, but we demonstrated that all analysed aquifers have been overexploited since much earlier than 2010. Finally, the Chilean aquifers' overexploitation is a clear example of the consequences of prioritising the water offer over the water demand regulation, which hinders the United Nations' sustainable development goals accomplishment.

Identifying hotspots of water table depth change by coupling trend with time stability analysis in the North China Plain

Many groundwater construction projects such as South-to-North Water Diversion Project (SNWDP) were conducted for controlling groundwater overexploitation in the North China Plain (NCP). However, more insight is required into the magnitude and distribution of water table depth (WTD) in time and space over the NCP. This study evaluated the variability and the hotspots of WTD based on 83 unconfined monitoring wells and took trend, breakpoint, and time stability into consideration. We found the average WTD of unconfined aquifer for the Southern Hebei Plain generally increased continuously from 1998 to 2020 in spite of the operation of the SNWDP since 2014. However, the rise rate of WTD slows down in recent years and the WTD has decreased in certain subregions. We further divided these groundwater wells into five groups: climb accelerating (Group 1), increase decelerating (Group 2), first rise then descend (Group 3), first descend then rise (Group 4), decrease decelerating (Group 5), and reduce accelerating (Group 6). Moreover, we found that the number of wells that divided into Group1 to Group 5 account for 15 %, 41 %, 25 %, 18 %, and 1 % of the total number of observation wells. The breakpoints of all the wells are from 2001 to 2017 and most of the breakpoints were found before 2014, which demonstrates that other groundwater management strategies implemented in the Southern Hebei Plain prior to the operation of the SNWDP plays a crucial part. The hotspots area for group 1 is mainly distributed in the north region of Shijiazhuang City, group 2 is in southern region of piedmont plain, group 3 is in northern region of Baoding and south-west region of Xingtai City, and group 4 is in Cangzhou City and eastern region of Xingtai City. The method and framework of this study can be applied in other regions suffering from groundwater depletion.

Controlled-Release Materials for Remediation of Trichloroethylene Contamination in Groundwater

Groundwater contamination by trichloroethylene (TCE) presents a pressing environmental challenge with far-reaching consequences. Traditional remediation methods have shown limitations in effectively addressing TCE contamination. This study reviews the limitations of conventional remediation techniques and investigates the application of oxidant-based controlled-release materials, including encapsulated, loaded, and gel-based potassium permanganate since the year 2000. Additionally, it examines reductant controlled-release materials and electron donor-release materials such as tetrabutyl orthosilicate (TBOS) and polyhydroxybutyrate (PHB). The findings suggest that controlled-release materials offer a promising avenue for enhancing TCE degradation and promoting groundwater restoration. This study concludes by highlighting the future research directions and the potential of controlled-release materials in addressing TCE contamination challenges.

Sources and transformation of nitrogen in shallow aquifers with progressive water table recovery using geochemical and isotopic approaches

Groundwater level recovery has a significant effect on the sources and transformation of nitrogen in groundwater, but there are still few studies on the influences of the water table on the sources and transformation of nitrogen in groundwater using field data. In this study, the changes in groundwater level, geochemical composition, and isotopic signatures of NO3- and NH4+ during a period of groundwater level recovery at a pilot site were analyzed in detail. The water table underwent progressive recovery of almost 1.6 m in 16 months. At a depth of 5.5 m below the surface, both low NH4+ and high NO3- appeared in the groundwater, whereas below that depth, both high NH4+ and low NO3- simultaneously appeared in the groundwater. The main sources of NO3- were manure and septic waste, and NH4+ fertilizers. The main sources of NH4+ were mineral fertilizers. The main transformation process were nitrification and denitrification at a depth of 5.5 m below the surface; below that depth, the main transformation processes were denitrification and dissimilatory nitrate reduction to ammonium (DNRA). This study provides a theoretical understanding of the relationship between the changing water table and nitrogen in groundwater level recovery areas.

Satellites reveal hotspots of global river extent change

Rivers are among the most diverse, dynamic, and productive ecosystems on Earth. River flow regimes are constantly changing, but characterizing and understanding such changes have been challenging from a long-term and global perspective. By analyzing water extent variations observed from four-decade Landsat imagery, we here provide a global attribution of the recent changes in river regime to morphological dynamics (e.g., channel shifting and anabranching), expansion induced by new dams, and hydrological signals of widening and narrowing. Morphological dynamics prevailed in ~20% of the global river area. Booming reservoir constructions, mostly skewed in Asia and South America, contributed to ~32% of the river widening. The remaining hydrological signals were characterized by contrasting hotspots, including prominent river widening in alpine and pan-Arctic regions and narrowing in the arid/semi-arid continental interiors, driven by varying trends in climate forcing, cryospheric response to warming, and human water management. Our findings suggest that the recent river extent dynamics diverge based on hydroclimate and socio-economic conditions, and besides reflecting ongoing morphodynamical processes, river extent changes show close connections with external forcings, including climate change and anthropogenic interference.

Analyzing past and future trends in Pakistan's groundwater irrigation development: implications for environmental sustainability and food security

Since the last four decades, groundwater irrigation has played a critical role in improving crop production and rural livelihoods. However, the flawed policies have allowed farmers to install private tube wells relentlessly, resulting in a slew of water quality and environmental issues. This study aims to investigate the key trends in temporal development of groundwater irrigation and its consequences in Pakistan. The dataset, which spanned 38 years (1981 to 2018), included variables such as the number of tube wells, wheat area and production, farm size, total cultivated area, and total irrigated area in Punjab province. Our results show that, while the number of government-installed tube wells has decreased over time, the number of private tube wells has increased by 579% since 1981. About 85% of these privately owned tube wells are diesel tube wells, while the remaining 15% are electric tube wells. The ARDL regression results show that groundwater development, as a result of growth in private tube wells, has significantly aided wheat production in both the short and long run. However, the results of ARIMA model show that, in the absence of any regulatory mechanism to limit private tube well growth, the number of private tube wells in Punjab will increase by 43% over the next two decades, potentially jeopardizing the country's groundwater sustainability and food security. To ensure the sustainability of groundwater use, farmers' incomes, and the food security of the population, there is an urgent need to devise policy options to limit the growth of probate tube wells in the province. In addition, the new regulations should consider the equity implications and the economic shock to poor farms and households.

An overview of the methods for evaluating the resilience of groundwater systems

Currently, groundwater resources are under anthropogenic and natural pressures. Depending on various factors, aquifers have diverse responses toward stresses. Resilience is among the performance criteria determining the ability of an aquifer to withstand unfavorable circumstances and to recover to a steady state after a failure. Hence, making use of this concept in groundwater systems is of cruciality in sustainable groundwater resources management. The main objective of the current research is to provide an overview on the employed procedures and existing difficulties appertaining to the appraisal of groundwater resilience. To this end, 36 studies which have evaluated groundwater resilience were regarded. Results highlighted that not only a very limited literature has employed groundwater resilience, but there also exist multiple knowledge gaps and complications, including resilience dimension, data scarcity and inaccuracies. In terms of groundwater quality and saltwater intrusion much little research exist, i.e. 7 studies among 36 ones. Evaluating groundwater resilience quantitatively, 11 methods were distinguished, each of which with its own advantages and disadvantages which may be engaged depending on factors such as available data and type of aquifer. Finally, more groundwater resilience analyses must be conducted at different spatiotemporal scales in order to preserve aquifers for the future generations. In summary, followings may be regarded to evaluate groundwater resilience:•To begin with, it must be specified which aspect of the aquifer's resilience and toward which unsatisfactory condition is planned to be considered.•Provided that no groundwater modeling is intended to be conducted, the observation data may be analyzed, considering the current state, governing violations, and new steady state.•On condition that groundwater simulation is planned to be conducted, subsequent to model's calibration and verification, the response of the aquifer, as a resilience criterion, is determined.

Effects of elevated arsenic and nitrate concentrations on groundwater resources in deltaic region of Sundarban Ramsar site, Indo-Bangladesh region

An attempt has been adopted to predict the As and NO₃^- concentration in groundwater (GW) in fast-growing coastal Ramsar region in eastern India. This study is focused to evaluate the As and NO₃^- vulnerable areas of coastal belts of the Indo-Bangladesh Ramsar site a hydro-geostrategic region of the world by using advanced ensemble ML techniques including NB-RF, NB-SVM and NB-Bagging. A total of 199 samples were collected from the entire study area for utilizing the 12 GWQ conditioning factors. The predicted results are certified that NB-Bagging the most suitable and preferable model in this current research. The vulnerability of As and NO₃^- concentration shows that most of the areas are highly vulnerable to As and low to moderately vulnerable to NO₃. The reliable findings of this present study will help the management authorities and policymakers in taking preventive measures in reducing the vulnerability of water resources and corresponding health risks.

Using Satellite-Based Terrestrial Water Storage Data: A Review

Land water storage plays a key role for the Earth's climate, natural ecosystems, and human activities. Since the launch of the first Gravity Recovery and Climate Experiment (GRACE) mission in 2002, spaceborne observations of changes in terrestrial water storage (TWS) have provided a unique, global perspective on natural and human-induced changes in freshwater resources. Even though they have become much used within the broader Earth system science community, space-based TWS datasets still incorporate important and case-specific limitations which may not always be clear to users not familiar with the underlying processing algorithms. Here, we provide an accessible and illustrated overview of the measurement concept, of the main available data products, and of some frequently encountered technical terms and concepts. We summarize concrete recommendations on how to use TWS data in combination with other hydrological or climatological datasets, and guidance on how to avoid possible pitfalls. Finally, we provide an overview of some of the main applications of GRACE TWS data in the fields of hydrology and climate science. This review is written with the intention of supporting future research and facilitating the use of satellite-based terrestrial water storage datasets in interdisciplinary contexts.

Impacts of Human Activities and Climate Change on Water Storage Changes in Shandong Province, China

The over-exploitation of water resources causes water resource depletion, which threatens water security, human life, and social and economic development. Only by clarifying the spatial pattern, changing trends, and influencing factors of water storage can we promote the rational development of water resources and relieve the pressure on water resources. However, there is still a lack of research on these aspects. In this study, the water-scarce area in Shandong Province, China, was selected to quantify the spatial and temporal changes in the terrestrial water storage (TWS) and groundwater storage (GWS) over the past 30 years. Nighttime light data were used to characterize the urbanization level (UL) and explore the effects of human activities (i.e., UL) and climate change (temperature and precipitation) on the TWS and GWS. The results show that 1) from 1990 to 2018, the overall TWS exhibited a significant decreasing trend (- 0.084 cm yr^-1). The change trend of the GWS was consistent with that of the TWS (- 0.516 m³ yr^-1). Spatially, there was significant spatial heterogeneity in the trend of the TWS and GWS. At the grid and prefectural scales, the TWS mainly exhibited a downward trend in the central and western regions, and an upward trend in the eastern region of Shandong Province. For the GWS, all cities exhibited a decreasing trend at the prefectural scale, whereas 92% of the regions exhibited a decreasing trend with less spatial heterogeneity at the grid scale. 2) Precipitation was the mean factor controlling the total amount of TWS and GWS in Shandong Province. Precipitation and temperature positively affected water storage, and the UL negatively affected it. At the prefectural scale, except for a few cities which were greatly influenced by the UL, the dominant factor of the TWS and GWS was precipitation in the other cities. At the grid scale, for the TWS, precipitation was the predominant factor in 51.82% of the entire region, followed by the UL (44.14%) and temperature (4.04%). For the GWS, precipitation was the predominant factor in 55.73% of the area, and the other 44.27% of the area was mainly influenced by the UL. Overall, precipitation and the UL were the key factors affecting the TWS and GWS. The results of this study provide a theoretical and decision-making basis for the optimal allocation and sustainable use of regional water resources.

Drying in the low-latitude Atlantic Ocean contributed to terrestrial water storage depletion across Eurasia

Eurasia, home to ~70% of global population, is characterized by (semi-)arid climate. Water scarcity in the mid-latitude Eurasia (MLE) has been exacerbated by a consistent decline in terrestrial water storage (TWS), attributed primarily to human activities. However, the atmospheric mechanisms behind such TWS decline remain unclear. Here, we investigate teleconnections between drying in low-latitude North Atlantic Ocean (LNATO) and TWS depletions across MLE. We elucidate mechanistic linkages and detecte high correlations between decreased TWS in MLE and the decreased precipitation-minus-evapotranspiration (PME) in LNATO. TWS in MLE declines by ~257% during 2003-2017 due to northeastward propagation of PME deficit following two distinct seasonal landfalling routes during January-May and June-January. The same mechanism reduces TWS during 2031-2050 by ~107% and ~447% under scenarios SSP245 and SSP585, respectively. Our findings highlight the risk of increased future water scarcity across MLE caused by large-scale climatic drivers, compounding the impacts of human activities.

Total water storage in Eurasia can be driven by both climate variability and human activities, with the latter suggested as the key factor for water loss. However, here the authors show that drying in the low-latitude Atlantic Ocean is the dominant force in storage depeletion during 2003-2017.

Managing Land Carrying Capacity: Key to Achieving Sustainable Production Systems for Food Security

Many previous studies have estimated the carrying capacity and feasible planetary boundaries for humankind. However, less attention has been given to how we will sustainably feed 9 billion people in 2050 and beyond. Here, we review the major natural resources that limit food production and discuss possible options, measures, and strategies to sustainably feed a human population of 9 billion in 2050 and beyond. Currently, food production greatly depends on external inputs, e.g., irrigation water and fertilizers, but these approaches are not sustainable. Due to the unbalanced distribution of global natural resources and large regional differences, urbanization expansion causes important areas to face more serious arable land resource shortages. Hence, sustainably feeding 9 billion people in 2050 and beyond remains an immense challenge for humankind, and this challenge requires novel planning and better decision-making tools. Importantly, the measures and strategies employed must be region-/country-specific because of the significant differences in the socioeconomic characteristics and natural environmental carrying capacity in different parts of the world. Considering the impact of unexpected extreme events (e.g., a global pandemic and war) in the future, the food trade and translocation of goods will also face challenges, and the strategies and decision-making processes employed must consider the possible influences at both regional and global scales.

Sustaining aquifers economically in the face of hydrologic, institutional, and climate constraints

Aquifers supply water to millions of farms, thousands of cities, and billions of people worldwide. Water use and economic activity in aquifer-dependent regions cannot be sustained if groundwater levels are not stabilized. This article addresses a question relevant to these regions internationally: how can water scarce areas reduce aquifer depletion while supporting the many economically and institutionally important uses of groundwater, which serve as a critical source of supply in many parts of the world with limited or seasonal precipitation which could become more pronounced in the face of future climate stress. Facing that challenge, this work presents a framework for discovering measures to hydrologically stabilize aquifers that control economic losses while respecting local institutional constraints. It advances our capacity to discover measures to efficiently, equitably, and sustainably allocate burden sharing that protects aquifers while adapting to hydrologic, economic, and institutional characteristics of an affected community. Results of this work show that for the aquifers investigated, present practices of groundwater use are unsustainable and finds that alternative practices are possible. It provides scenarios describing such practices and also determines their hydrological and economic consequences. Finally, it shows how these results can feed into policy debates over the several water-sharing arrangements. This work makes several incremental contributions: calibrating modelled pumping patterns to the historical baseline, controlling economic costs of achieving hydrologic sustainability, respecting institutional constraints governing equitable burden sharing, presenting an approach with powers of generalizability, and using routinely collected data. While the approach and findings are illustrated for two aquifers in Africa, its approach carries some generalizability. All data, variables, equations, constraints, and results are included as appendices.

Recent Changes in Groundwater and Surface Water in Large Pan-Arctic River Basins

Surface and groundwater in large pan-Arctic river basins are changing rapidly. High-quality estimates of these changes are challenging because of the limits on the data quality and time span of satellite observations. Here, the term pan-Arctic river refers to the rivers flowing to the Arctic Ocean basin. In this study, we provide a new evaluation of groundwater storage (GWS) changes in the Lena, Ob, Yenisei, Mackenzie and Yukon River basins from the GRACE total water storage anomaly product, in situ runoff, soil moisture form models and a snow water equivalent product that has been significantly improved. Seasonal Trend decomposition using Loess was utilized to obtain trends in GWS. Changes in surface water (SW) between 1984 and 2019 in these basins were also examined based on the Joint Research Centre Global Surface Water Transition data. Results suggested that there were great GWS losses in the North American river basins, totaling approximately −219 km3, and GWS gains in the Siberian river basins, totaling ~340 km3, during 2002–2017. New seasonal and permanent SWs are the primary contributors to the SW transition, accounting for more than 50% of the area of the changed SW in each basin. Changes in the Arctic hydrological system will be more significant and various in the case of rapid and continuous changes in permafrost.

Geometric Model of a Coastal Aquifer to Promote the Sustainable Use of Water. Manglaralto, Ecuador

Modeling an aquifer provides significant advantages when evaluating and estimating the water resource for its sustainable use. This study focuses on the rural parish Manglaralto, a semi-arid area with a shortage of water, and without supply service by the public network. Still, it has a great demand for supply by the local and floating population (tourism). This has caused the coastal aquifer, which supplies the area’s water, to show signs of overexploitation, and its natural balance is compromised. The aim is to establish a geometric model of the aquifer through geological and geophysical analysis to set sustainable water-use guidelines. The methodology includes: (i) the processing of the current technical and hydrogeological information to know the aquifer’s data; (ii) geometric modeling of the aquifer through the correlation of technical information, using the GeoModeller software; (iii) proposals for the sustainable use of water in the framework of the United Nations’ Agenda 2030. The geometric model results reveal that the aquifer’s thickness varies from 4 m at the head of the river to 30 m at the sea’s mouth. The volume of water is estimated at 13.6 Hm3. The sustainable-use proposals ensure that more than half of the population receives the community company’s service. More than 40% of the territory is a protected area, and 64% of the population has sewerage service. This geometric model is a visual contribution that allows us to know the aquifer’s shape and establishes guidelines that help strengthen the water supply’s development and sustainability over time.

Groundwater recharge potential zonation using an ensemble of machine learning and bivariate statistical models

Many regions in Iran are currently experience water crisis, largely driven by frequent droughts and expanding agricultural land combined with over abstraction of groundwater. Therefore, it is extremely important to identify potential groundwater recharge (GWR) zones to help in prevent water scarcity. The key objective of this research is to applying different scenarios for GWR potential mapping by means of a classifier ensemble approach, namely a combination of Maximum Entropy (ME) and Frequency Ratio (FR) models in a semi-arid mountainous, Marboreh Watershed of Iran. To consider the ensemble effect of these models, 15 input layers were generated and used in two models and then the models were combined in seven scenarios. According to marginal response curves (MRCs) and the Jackknife technique, quaternary formations (Qft1 and Qft2) of lithology, sandy-clay-loam (Sa. Cl. L) class of soil, 0–4% class of slope, and agriculture & rangeland classes of land use, offered the highest percolation potential. Results of the FR model showed that the highest weight belonged to Qft1 rocks and Sa. Cl. L textures. Seven scenarios were used for GWR potential maps by different ensembles based on basic mathematical operations. Correctly Classified Instances (CCI), and the AUC indices were applied to validate model predictions. The validation indices showed that scenarios 5 had the best performance. The combination of models by different ensemble scenarios enhances the efficiency of these models. This study serves as a basis for future investigations and provides useful information for prediction of sites with groundwater recharge potential through combination of state-of-the-art statistical and machine learning models. The proposed ensemble model reduced the machine learning and statistical models’ limitations gaps and promoted the accuracy of the model where combining, especially for data-scarce areas. The results of present study can be used for the GWR potential mapping, land use planning, and groundwater development plans.

Spatial–Temporal Evolution Characteristics and Influencing Factors of Agricultural Water Use Efficiency in Northwest China—Based on a Super-DEA Model and a Spatial Panel Econometric Model

Improving agricultural water use efficiency (AWUE) is an important way to solve the shortage of water resources in arid and semi-arid regions. This study used the Super-DEA (data envelopment analysis) to measure the AWUE of 52 cities in Northwest China from 2000 to 2018. Based on spatial and temporal perspectives, it applied Exploratory Spatial Data Analysis (ESDA) to explore the dynamic evolution and regional differences of AWUE. A spatial econometric model was then used to analyze the main factors that influence the AWUE in Northwest China. The results showed firstly that the overall AWUE in Northwest China from 2000 to 2018 presented a steady upward trend. However, only a few cities achieved effective agricultural water usage by 2018, and the differences among cities were obvious. Secondly, AWUE showed an obvious spatial autocorrelation in Northwest China and showed significant high–high and low–low agglomeration characteristics. Thirdly, economic growth, urbanization development, and effective irrigation have significant, positive effects on AWUE, while per capita water resource has a significant, negative influence. Finally, when improving the AWUE in arid and semi-arid regions, plans should be formulated according to local conditions. The results of this study can provide new ideas on the study of AWUE in arid and semi-arid regions and provide references for the formulation of regional agricultural water resource utilization policies as well.

Adsorption and Photocatalytic Mineralization of Bromophenol Blue Dye with TiO2 Modified with Clinoptilolite/Activated Carbon

This study presents a hybridized photocatalyst with adsorbate as a promising nanocomposite for photoremediation of wastewater. Photocatalytic degradation of bromophenol blue (BPB) in aqueous solution under UV-irradiation of wavelength 400 nm was carried out with TiO2 doped with activated carbon (A) and clinoptilolite (Z) via the co-precipitation technique. The physiochemical properties of the nanocomposite (A–TiO2 and Z–TiO2) and TiO2 were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared (FTIR) spectroscopy. Results of the nanocomposite (A–TiO2 and Z–TiO2) efficiency was compared to that with the TiO2, which demonstrated their adsorption and synergistic effect for the removal of chemical oxygen demand (COD) and color from the wastewater. At an optimal load of 4 g, the photocatalytic degradation activity (Z–TiO2 > A–TiO2 > TiO2) was found favorably by the second-order kinetic model. Consequently, the Langmuir adsorption isotherms favored the nanocomposites (Z–TiO2 > A–TiO2), whereas that of the TiO2 fitted very well on the Freundlich isotherm approach. Z–TiO2 evidently exhibited a high photocatalytic efficacy of decomposition over 80% of BPB (COD) at reaction rate constant (k) and coefficient of determination (R2) values of 5.63 × 10−4 min−1 and 0.989, respectively.

Groundwater Resilience Assessment in a Communal Coastal Aquifer System. The Case of Manglaralto in Santa Elena, Ecuador

Resilience has several meanings, among them the ability to overcome difficulty and return to the state of providing service, even if the initial conditions change. Assessing resilience in an ecosystem, or any system, requires a concise methodology with standard variables and parameters. The current challenge presented by coastal areas is focused on overcoming problems related to the water supply through correct management. This paper aims to evaluate the communal coastal aquifer system with a matrix for assessing water resilience based on indicators in the Sustainable Development Goals (SDGs) in a socio-hydrological framework and the four axes of development (political, social, environmental, and cultural), to promote the development of new strategies for water sustainability. The method is based on (i) political, economic, social, environmental, and even cultural aspects involved in sustainable water management and (ii) the groundwater resilience assessment method (GRAM) design. The GRAM is used for a quasi-quantitative assessment of the resilience in a communal coastal aquifer system. This method was applied to the Manglaralto community; the results show a highly resilient groundwater system (62.33/100 points). Representatives of the community have achieved appropriate use, management, and conservation of the water resource by applying water harvesting and other technical criteria. Hence, they have avoided aquifer overexploitation and provided water to the community.

Seepage Velocity: Large Scale Mapping and the Evaluation of Two Different Aquifer Conditions (Silty Clayey and Sandy)

Seepage velocity is a very important criterion in infrastructure construction. The planning of numerous large infrastructure projects requires the mapping of seepage velocity at a large scale. To date, however, no reliable approach exists to determine seepage velocity at such a scale. This paper presents a tool within ArcMap/Geographic Information System (GIS) software that can be used to map the seepage velocity at a large scale. The resultant maps include both direction and magnitude mapping of the seepage velocity. To verify the GIS tool, this study considered two types of aquifer conditions in two regions in Iraq: silty clayey (Babylon province) and sandy (Dibdibba in Karbala province). The results indicate that, for Babylon province, the groundwater flows from the northwest to southeast with a seepage velocity no more than 0.19 m/d; for the Dibdibba region, the groundwater flows from the west to the east with a seepage velocity not exceeding 0.27 m/d. The effectiveness of the presented tool in depicting the seepage velocity was thus demonstrated. The accuracy of the resultant maps depends on the resolution of the four essential maps (groundwater elevation head, effective porosity, saturated thickness, and transmissivity) and locations of wells that are used to collect the data.

South-to-North Water Diversion stabilizing Beijing's groundwater levels

Groundwater (GW) overexploitation is a critical issue in North China with large GW level declines resulting in urban water scarcity, unsustainable agricultural production, and adverse ecological impacts. One approach to addressing GW depletion was to transport water from the humid south. However, impacts of water diversion on GW remained largely unknown. Here, we show impacts of the central South-to-North Water Diversion on GW storage recovery in Beijing within the context of climate variability and other policies. Water diverted to Beijing reduces cumulative GW depletion by ~3.6 km³, accounting for 40% of total GW storage recovery during 2006-2018. Increased precipitation contributes similar volumes to GW storage recovery of ~2.7 km³ (30%) along with policies on reduced irrigation (~2.8 km³, 30%). This recovery is projected to continue in the coming decade. Engineering approaches, such as water diversions, will increasingly be required to move towards sustainable water management.

South-to-North Water Diversion stabilizing Beijing's groundwater levels

Groundwater (GW) overexploitation is a critical issue in North China with large GW level declines resulting in urban water scarcity, unsustainable agricultural production, and adverse ecological impacts. One approach to addressing GW depletion was to transport water from the humid south. However, impacts of water diversion on GW remained largely unknown. Here, we show impacts of the central South-to-North Water Diversion on GW storage recovery in Beijing within the context of climate variability and other policies. Water diverted to Beijing reduces cumulative GW depletion by ~3.6 km³, accounting for 40% of total GW storage recovery during 2006–2018. Increased precipitation contributes similar volumes to GW storage recovery of ~2.7 km³ (30%) along with policies on reduced irrigation (~2.8 km³, 30%). This recovery is projected to continue in the coming decade. Engineering approaches, such as water diversions, will increasingly be required to move towards sustainable water management.

The authors here address water sustainability in the greater area of Beijing, China. Specifically, the positive effects towards Beijing groundwater levels via water diversion from the Yangtze River to the North are shown.

Environmental flow limits to global groundwater pumping

Groundwater is the world's largest freshwater resource and is critically important for irrigation, and hence for global food security^1-3. Already, unsustainable groundwater pumping exceeds recharge from precipitation and rivers⁴, leading to substantial drops in the levels of groundwater and losses of groundwater from its storage, especially in intensively irrigated regions^5-7. When groundwater levels drop, discharges from groundwater to streams decline, reverse in direction or even stop completely, thereby decreasing streamflow, with potentially devastating effects on aquatic ecosystems. Here we link declines in the levels of groundwater that result from groundwater pumping to decreases in streamflow globally, and estimate where and when environmentally critical streamflows-which are required to maintain healthy ecosystems-will no longer be sustained. We estimate that, by 2050, environmental flow limits will be reached for approximately 42 to 79 per cent of the watersheds in which there is groundwater pumping worldwide, and that this will generally occur before substantial losses in groundwater storage are experienced. Only a small decline in groundwater level is needed to affect streamflow, making our estimates uncertain for streams near a transition to reversed groundwater discharge. However, for many areas, groundwater pumping rates are high and environmental flow limits are known to be severely exceeded. Compared to surface-water use, the effects of groundwater pumping are markedly delayed. Our results thus reveal the current and future environmental legacy of groundwater use.

Long-term, non-anthropogenic groundwater storage changes simulated by three global-scale hydrological models

This study examined long-term, natural (i.e., excluding anthropogenic impacts) variability of groundwater storage worldwide. Groundwater storage changes were estimated by forcing three global-scale hydrological models with three 50+ year meteorological datasets. Evaluation using in situ groundwater observations from the U.S. and terrestrial water storage derived from the Gravity Recovery and Climate Experiment (GRACE) satellites showed that these models reasonably represented inter-annual variability of water storage, as indicated by correlations greater than 0.5 in most regions. Empirical orthogonal function analysis revealed influences of the El Niño Southern Oscillation (ENSO) on global groundwater storage. Simulated groundwater storage, including its global average, exhibited trends generally consistent with that of precipitation. Global total (natural) groundwater storage decreased over the past 5-7 decades with modeled rates ranging from 0.01 to 2.18 mm year^-1. This large range can be attributed in part to groundwater's low frequency (inter-decadal) variability, which complicates identification of real long-term trends even within a 50+ year time series. Results indicate that non-anthropogenic variability in groundwater storage is substantial, making knowledge of it fundamental to quantifying direct human impacts on groundwater storage.

Contributions of GRACE to understanding climate change

Time-resolved satellite gravimetry has revolutionized understanding of mass transport in the Earth system. Since 2002, the Gravity Recovery and Climate Experiment (GRACE) has enabled monitoring of the terrestrial water cycle, ice sheet and glacier mass balance, sea level change and ocean bottom pressure variations and understanding responses to changes in the global climate system. Initially a pioneering experiment of geodesy, the time-variable observations have matured into reliable mass transport products, allowing assessment and forecast of a number of important climate trends and improve service applications such as the U.S. Drought Monitor. With the successful launch of the GRACE Follow-On mission, a multi decadal record of mass variability in the Earth system is within reach.

Groundwater hydrodynamics of an Eastern Africa coastal aquifer, including La Niña 2016-17 drought

In 2016-17 much of East Africa was affected by a severe drought which has been attributed to Indian Ocean Dipole and El Niño Southern Oscillation conditions. Extreme events such as this have immediate and knock-on effects on water availability for household, agricultural and industrial use. Groundwater resources can provide a buffer in times of drought, but may themselves be stressed by reduced recharge and increased usage, posing significant challenges to groundwater resource management. In the context of East Africa, groundwater management is also hampered by a lack of information on aquifer characteristics. With the aim of addressing this knowledge gap, this study shows the hydrogeological behaviour before and during La Niña 2016/17 drought in southern coastal Kenya on a groundwater system which sits within a geological structure which is representative of an important portion of the East African coast. Diverse hydrochemical and isotopic campaigns, as well as groundwater head variation measurements, were carried out to study the groundwater hydrodynamics and thus characterize the aquifer system under climatic conditions before and during the La Niña event. This information is complemented with an estimation of changes in local recharge since 2012 using local data sets. The main consequence of the drought was a 69% reduction of recharge compared to an average climatic year. There was reduced recharge during the first rainy season (April-June) and no recharge during the second wet season (October-December). There was a concurrent increase in seawater intrusion even during the wet season.

The Potential Role of Halothiobacillus spp. in Sulfur Oxidation and Acid Generation in Circum-Neutral Mine Tailings Reservoirs

The biogeochemistry of acid mine drainage (AMD) derived from waste rock associated sulfide mineral oxidation is relatively well-characterized and linked to Acidithiobacillus spp.. However, little is understood about the microbial communities and sulfur cycling before AMD develops, a key component of its prevention. This study aimed to examine circum-neutral mining impacted water (MIW) communities and its laboratory enrichments for sulfur oxidizing bacteria (SoxBac). MIW in situ microbial communities differed in diversity, structure and relative abundance consistent with site specific variations in total aqueous sulfur concentrations (TotS; ~2-17 mM), pH (3.67-7.34), and oxygen (22-93% saturation). However, the sulfur oxidizer, Halothiobacillus spp. dominated seven of the nine total SoxBac enrichment communities (~76-100% relative abundance), spanning three of the four mines. The presence and relative abundance of the identified sixteen known and five unclassified Halothiobacillus spp. here, were the important clustering determinants across parent MIW and enrichment communities. Further, the presence of Halothiobacillus spp. was associated with driving the pH <4 in enrichment experiments, and the combination of specific Halothiobacillus spp. in the enrichments affected the observed acid to sulfate ratios indicating differential sulfur cycling. Halothiobacillus spp. also dominated the parent communities of the two acidic MIWs providing corroborating evidence for its active role in net acid generation within these waters. These results identify a putative indicator organism specific to mine tailings reservoirs and highlight the need for further study of tailings associated sulfur cycling for better mine management and environmental stewardship.

Evaluating the Dynamics of Groundwater Depletion for an Arid Land in the Tarim Basin, China

: Groundwater depletion has become a hotly debated topic, particularly in arid land. In this study, groundwater depletion and its dynamic factors were investigated in the Tarim Basin. The groundwater data were collected randomly from 10 groundwater monitoring wells, from September 2002–December 2014. Piezometric groundwater level decreased with the range from 667.00 cm to 1288.50 cm, and also with a linear decreasing rate of 73.96 cm per year, on average. Significant spatial variation characteristics have been detected. Groundwater depletion was more serious in the northwest than the southeast of the study area. A correlation analysis was conducted to explore the major influence factors. These results showed that the annual irrigated land area was the primary influencing factor. Driving force analysis also suggested that electricity consumption could be an effective and convenient factor to assess groundwater exploitation. This study indicated that human activity was the major impact factor for groundwater decline. The seasonal-trend decomposition analysis supported these findings, as observed from the correlation analysis and the spatial variation. It also provided new insight into the groundwater time-series and enhanced the identification of groundwater-flow characteristics. These findings may be useful for understanding the groundwater fluctuations in high water demand regions and also for developing safety policies for groundwater management.

Projecting groundwater storage changes in California's Central Valley

Accurate and detailed knowledge of California’s groundwater is of paramount importance for statewide water resources planning and management, and to sustain a multi-billion-dollar agriculture industry during prolonged droughts. In this study, we use water supply and demand information from California’s Department of Water Resources to develop an aggregate groundwater storage model for California’s Central Valley. The model is evaluated against 34 years of historic estimates of changes in groundwater storage derived from the United States Geological Survey’s Central Valley Hydrologic Model (USGS CVHM) and NASA’s Gravity Recovery and Climate Experiment (NASA GRACE) satellites. The calibrated model is then applied to predict future changes in groundwater storage for the years 2015–2050 under various precipitation scenarios from downscaled climate projections. We also discuss and project potential management strategies across different annual supply and demand variables and how they affect changes in groundwater storage. All simulations support the need for collective statewide management intervention to prevent continued depletion of groundwater availability.

The groundwater risk index: Development and application in the Middle East and North Africa region

Overreliance on predominantly non-renewable groundwater resources and their subsequent depletion has given rise to adverse environmental, political, economic, and social effects. The high costs of groundwater depletion are exacerbated by the notable absence of tools designed to identify and diagnose areas at risk of groundwater degradation. In this study, a Groundwater Risk Index (GRI) was developed as a distributed composite index to assess and evaluate groundwater depletion risk by combining different environmental and socioeconomic datasets and models. GRI is designed to be used by end-users (e.g. governments, NGOs) as a multicriteria diagnostic tool to identify and determine the probability and severity of an entity experiencing the adverse effects of groundwater mining. Annual GRI results indicate that groundwater risk is highly dependent on governance and food security. Surprisingly, groundwater storage reserves were indeterminate of groundwater risk. Given the centrality of agricultural production in groundwater consumptive use, MENA countries are recommended to mitigate groundwater depletion by establishing reliable and secure virtual water transfers (agricultural trade) to achieve food security, as opposed to unsustainably exploiting finite water resources for short-term food sufficiency. The GRI's design choices, including adopting an equal weighting scheme and a linear additive aggregation approach, promote structural flexibility that enables the modification, application, and implementation of the index in other semi- to hyper-arid regions with a high level of dependency on groundwater resources.

Emerging trends in global freshwater availability

Freshwater availability is changing worldwide. Here we quantify 34 trends in terrestrial water storage observed by the Gravity Recovery and Climate Experiment (GRACE) satellites during 2002-2016 and categorize their drivers as natural interannual variability, unsustainable groundwater consumption, climate change or combinations thereof. Several of these trends had been lacking thorough investigation and attribution, including massive changes in northwestern China and the Okavango Delta. Others are consistent with climate model predictions. This observation-based assessment of how the world's water landscape is responding to human impacts and climate variations provides a blueprint for evaluating and predicting emerging threats to water and food security.

Emerging trends in global freshwater availability

Freshwater availability is changing worldwide. Here we quantify 34 trends in terrestrial water storage observed by the Gravity Recovery and Climate Experiment (GRACE) satellites during 2002-2016 and categorize their drivers as natural interannual variability, unsustainable groundwater consumption, climate change or combinations thereof. Several of these trends had been lacking thorough investigation and attribution, including massive changes in northwestern China and the Okavango Delta. Others are consistent with climate model predictions. This observation-based assessment of how the world's water landscape is responding to human impacts and climate variations provides a blueprint for evaluating and predicting emerging threats to water and food security.

Land-Sparing Opportunities for Solar Energy Development in Agricultural Landscapes: A Case Study of the Great Central Valley, CA, United States

Land-cover change from energy development, including solar energy, presents trade-offs for land used for the production of food and the conservation of ecosystems. Solar energy plays a critical role in contributing to the alternative energy mix to mitigate climate change and meet policy milestones; however, the extent that solar energy development on nonconventional surfaces can mitigate land scarcity is understudied. Here, we evaluate the land sparing potential of solar energy development across four nonconventional land-cover types: the built environment, salt-affected land, contaminated land, and water reservoirs (as floatovoltaics), within the Great Central Valley (CV, CA), a globally significant agricultural region where land for food production, urban development, and conservation collide. Furthermore, we calculate the technical potential (TWh year^-1) of these land sparing sites and test the degree to which projected electricity needs for the state of California can be met therein. In total, the CV encompasses 15% of CA, 8415 km² of which was identified as potentially land-sparing for solar energy development. These areas comprise a capacity-based energy potential of at least 17 348 TWh year^-1 for photovoltaic (PV) and 2213 TWh year^-1 for concentrating solar power (CSP). Accounting for technology efficiencies, this exceeds California's 2025 projected electricity demands up to 13 and 2 times for PV and CSP, respectively. Our study underscores the potential of strategic renewable energy siting to mitigate environmental trade-offs typically coupled with energy sprawl in agricultural landscapes.

The measurement of water scarcity: Defining a meaningful indicator

Metrics of water scarcity and stress have evolved over the last three decades from simple threshold indicators to holistic measures characterising human environments and freshwater sustainability. Metrics commonly estimate renewable freshwater resources using mean annual river runoff, which masks hydrological variability, and quantify subjectively socio-economic conditions characterising adaptive capacity. There is a marked absence of research evaluating whether these metrics of water scarcity are meaningful. We argue that measurement of water scarcity (1) be redefined physically in terms of the freshwater storage required to address imbalances in intra- and inter-annual fluxes of freshwater supply and demand; (2) abandons subjective quantifications of human environments and (3) be used to inform participatory decision-making processes that explore a wide range of options for addressing freshwater storage requirements beyond dams that include use of renewable groundwater, soil water and trading in virtual water. Further, we outline a conceptual framework redefining water scarcity in terms of freshwater storage.

Groundwater intensive use and mining in south-eastern peninsular Spain: Hydrogeological, economic and social aspects

Intensive groundwater development is a common circumstance in semiarid and arid areas. Often abstraction exceeds recharge, thus continuously depleting reserves. There is groundwater mining when the recovery of aquifer reserves needs more than 50years. The MASE project has been carried out to compile what is known about Spain and specifically about the south-eastern Iberian Peninsula and the Canary Islands. The objective was the synthetic analysis of available data on the hydrological, economic, managerial, social, and ethical aspects of groundwater mining. Since the mid-20th century, intensive use of groundwater in south-eastern Spain allowed extending and securing the areas with traditional surface water irrigation of cash crops and their extension to former dry lands, taking advantage of good soils and climate. This fostered a huge economic and social development. Intensive agriculture is a main activity, although tourism plays currently an increasing economic role in the coasts. Many aquifers are relatively high yielding small carbonate units where the total groundwater level drawdown may currently exceed 300m. Groundwater storage depletion is estimated about 15km(3). This volume is close to the total contribution of the Tagus-Segura water transfer, but without large investments paid for with public funds. Seawater desalination complements urban supply and part of cash crop cultivation. Reclaimed urban waste water is used for irrigation. Groundwater mining produces benefits but associated to sometimes serious economic, administrative, legal and environmental problems. The use of an exhaustible vital resource raises ethical concerns. It cannot continue under the current legal conditions. A progressive change of water use paradigm is the way out, but this is not in the mind of most water managers and politicians. The positive and negative results observed in south-eastern Spain may help to analyse other areas under similar hydrogeological conditions in a less advanced stage of water use evolution.

Have GRACE satellites overestimated groundwater depletion in the Northwest India Aquifer?

The Northwest India Aquifer (NWIA) has been shown to have the highest groundwater depletion (GWD) rate globally, threatening crop production and sustainability of groundwater resources. Gravity Recovery and Climate Experiment (GRACE) satellites have been emerging as a powerful tool to evaluate GWD with ancillary data. Accurate GWD estimation is, however, challenging because of uncertainties in GRACE data processing. We evaluated GWD rates over the NWIA using a variety of approaches, including newly developed constrained forward modeling resulting in a GWD rate of 3.1 ± 0.1 cm/a (or 14 ± 0.4 km³/a) for Jan 2005–Dec 2010, consistent with the GWD rate (2.8 cm/a or 12.3 km³/a) from groundwater-level monitoring data. Published studies (e.g., 4 ± 1 cm/a or 18 ± 4.4 km³/a) may overestimate GWD over this region. This study highlights uncertainties in GWD estimates and the importance of incorporating a priori information to refine spatial patterns of GRACE signals that could be more useful in groundwater resource management and need to be paid more attention in future studies.

Assessing Global Water Storage Variability from GRACE: Trends, Seasonal Cycle, Subseasonal Anomalies and Extremes

Throughout the past decade, the Gravity Recovery and Climate Experiment (GRACE) has given an unprecedented view on global variations in terrestrial water storage. While an increasing number of case studies have provided a rich overview on regional analyses, a global assessment on the dominant features of GRACE variability is still lacking. To address this, we survey key features of temporal variability in the GRACE record by decomposing gridded time series of monthly equivalent water height into linear trends, inter-annual, seasonal, and subseasonal (intra-annual) components. We provide an overview of the relative importance and spatial distribution of these components globally. A correlation analysis with precipitation and temperature reveals that both the inter-annual and subseasonal anomalies are tightly related to fluctuations in the atmospheric forcing. As a novelty, we show that for large regions of the world high-frequency anomalies in the monthly GRACE signal, which have been partly interpreted as noise, can be statistically reconstructed from daily precipitation once an adequate averaging filter is applied. This filter integrates the temporally decaying contribution of precipitation to the storage changes in any given month, including earlier precipitation. Finally, we also survey extreme dry anomalies in the GRACE record and relate them to documented drought events. This global assessment sets regional studies in a broader context and reveals phenomena that had not been documented so far.