Groundwater Storage Depletion Research Articles

Analysis of groundwater changes (2003–2020) in the North China Plain using geodetic measurements

Study regionNorth China Plain (NCP), China. Study focusThis paper investigates the spatiotemporal characteristics of groundwater storage (GWS) changes in the NCP during 2003–2020 using Gravity Recovery and Climate Experiment (GRACE) and Global Navigation Satellite System (GNSS) measurements with a focus on the subperiods separated by the implementation (December 2014) of the South-to-North Water Diversion Middle Route Project (MRP). New hydrological insights for the regionGRACE-derived results demonstrate that GWS depleted at rates of − 1.66 ± 0.17 cm/yr and − 2.76 ± 0.55 cm/yr for subperiods of 2003–2014 and 2015–2020, respectively, suggesting that GWS continued decreasing after the MRP. However, the spatial distribution of average monthly GWS shows an evident southwest-northeast band distribution, and the GWS depletion in the northwest has been alleviated compared with the southeast. The GNSS stations in the Beijing area show accelerated increasing rates of vertical displacements, while those in the plain areas of Hebei and Tianjin show continuous declining rates, implying that GWS in the Beijing area recovered faster after the MRP, while the GWS depletion in plain areas of Hebei and Tianjin continued. In addition, precipitation is the main driving factor to GWS variability during the whole study period, with grey correlation coefficients of 0.66–0.75. This strong correlation explains the significant reduction in GWS caused by the large precipitation deficit in 2019, which leads to a larger GWS depletion rate for the 2015–2020 period.

Comparison of the shallow groundwater storage change estimated by a distributed hydrological model and GRACE satellite gravimetry in a well-irrigated plain of the Haihe River basin, China

Groundwater is a key component of the global hydrological cycle. Quantitative approaches to estimate the spatial and temporal changes in groundwater storage (GWS) could provide solid foundation for sustainable management. This study made a comprehensive comparison of GWS changes based on two independent approaches: the Soil and Water Assessment Tool (SWAT) hydrological model and Gravity Recovery and Climate Experiment (GRACE) satellite mission data. The feasibility of using these two estimation methods to quantify shallow groundwater variations in the Haihe River basin of China, a globally representative overexploited area, was assessed. The GRACE-derived GWS changes were calculated based on independent component analysis and a joint inversion method. The results showed that the GRACE-estimated shallow GWS anomalies during 2003–2012 agree well with the SWAT-simulated data. For the variations in the long-term GWS depletion rate, we found that heterogeneity at 22 subbasin (approximately 500 to 1500 km2) scales was detected by the GRACE data, and these results were spatially coherent with the SWAT simulations based on the distributed modeling units and multiple inputs. The GRACE estimates could adequately replicate the general trends of GWS depletion in the winter wheat (Triticum aestivum L.) growth period and recovery in the summer maize (Zea mays L.) growth period. Specifically, comparisons between GRACE-based and SWAT-simulated results indicated that the signals of pumping for winter wheat irrigation in several key water requirement periods in April, May and November were identified by GRACE, as were seasonal changes in shallow GWS (e.g., an obvious depletion in spring). Despite an overestimation of the scope of the fluctuations in GRACE estimates compared with those of SWAT simulations from the perspective of the water flux, the effective identification of the impact of anthropogenic exploitation on shallow GWS in GRACE suggests that this monitoring tool could be applied in the groundwater management of this plain. This study demonstrated a good agreement between SWAT-simulated and GRACE-based shallow GWS changes from the perspectives of long-term trends and variations in crop seasons. Additionally, satisfactory consistency was observed from the perspective of the water flux in this semiarid and semihumid study region considering the influence of human activities.

Long term influence of groundwater preservation policy on stubble burning and air pollution over North-West India

Stubble burning (SB) has been a major source of seasonal aerosol loading and pollution over northern India. The aftereffects of groundwater preservation act i.e., post 2010 era (2011–2020) has seen delay in crop harvesting thereby shifting the peak SB to May (Wheat SB) and to November (Paddy SB) by 8–10 and 10–12 days compared to pre-2010. Groundwater storage depletion rate of 29.2 mm yr−1 was observed over the region. Post 2010 era shows an increase of 1.4% in wheat SB and 21% in Paddy SB fires over Punjab and Haryana with 70% of PM2.5 air mass clusters (high probability > 0.8) advecting to the downwind regions leading to 23–26% increase in PM2.5 and 4–6% in aerosol loading over National Capital Region (NCR). Although the objective of water conservation policy was supposed to preserve the groundwater by delaying the paddy transplantation and sowing, on the contrary the implementation of this policy has seen groundwater storage after 2013 depleting at a rate of 29.2 mmyr−1 over these regions. Post policy implementation has led to shift and shrinking of harvest window with increased occurrences in SB fires which also increase associated particulate matter pollution over North India.

Evaluation of Groundwater Storage Depletion Using GRACE/GRACE Follow-On Data with Land Surface Models and Its Driving Factors in Haihe River Basin, China

Groundwater storage (GWS) in the Haihe River Basin (HRB), which is one of the most densely populated and largest agricultural areas in China, is of great importance for the ecosystem environment and socio-economic development. In recent years, large-scale overexploitation of groundwater in HRB has made it one of the global hotspots of GWS depletion. In this study, monthly GWS variations in HRB from 2003 to 2020 were estimated using the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) data in combination with three land surface models (LSMs) from the Global Land Data Assimilation System (GLDAS). The results show the following: (1) HRB suffered extensive GWS depletion from 2003 to 2020, which has been aggravated since 2014, with a mean rate of 1.88 cm·yr−1, which is equivalent to a volume of 6 billion m3·yr−1. The GWS depletion is more serious in the plain zone (−2.36 cm·yr−1) than in the mountainous zone (−1.63 cm·yr−1). (2) Climate changes are excluded from the reasons for GWS depletion due to annual precipitation and evaporation being close to normal throughout the period. In addition, GWS changes show a low correlation with meteorological factors. (3) The consumption of groundwater for irrigation and land use/cover changes have been confirmed to be the dominant factors for GWS depletion in HRB. (4) The effects of inter-basin water transfer projects cannot be obviously observed using the GRACE and GRACE-FO; more inter-basin water transfers are needed for recovering the GWS in HRB. Therefore, it is imperative to control groundwater exploitation and develop a more economical agricultural irrigation structure for the sustainability of groundwater resources in HRB.

Assessment of groundwater drought vulnerability and delineation of sites for artificial recharge – a case study

Drought impacts both surface water and groundwater, which leads to reduced supply. Groundwater drought indicates continuous depletion of groundwater level, storage and discharge. Assessment of groundwater drought conditions is necessary for effective planning of drought management strategies. In this study, the drought vulnerability of Chittur Block in Palakkad, Kerala is assessed by the occurrence of groundwater drought and is mapped using geographic information system (GIS). A strategy for the effective implementation of artificial recharge schemes is proposed to combat future drought conditions. A combination of GIS and weighted parameter approach (WPA) is employed to delineate safe, suitable locations for artificial groundwater recharge. Site specific recharging structures such as check dams, infiltration pits, injection wells and percolation ponds are recommended within the 65% area which was identified as most conducive for artificial recharge.

Quantifying the influence of long-term overexploitation on deep groundwater resources across Cangzhou in the North China Plain using InSAR measurements

Deep groundwater (confined groundwater) is the major water source in Cangzhou, situated in the North China Plain. Long-term deep groundwater overexploitation has resulted in substantial groundwater storage (GWS) depletion. Quantifying the influence of long-term overexploitation on deep groundwater resources is extremely important to maintain the sustainability of the confined aquifer system. In this study, we estimate the amount of total exploitable GWS and total GWS depletion during 1960–2010 in the confined aquifer system across Cangzhou by combining use of the InSAR deformation, estimated skeletal storativity, hydraulic head observations, and hydrogeological data. The total exploitable GWS in Cangzhou was 26.1 ± 21.3 km3 and decreased by 13.0 ± 8.1 km3 ∼ 13.6 ± 8.5 km3 until 2010, accounting for 49.8%∼52.2% of the total amount. It is worth noting that 87.4%∼87.9% of the total GWS depletion is irreversible, leading to a substantial permanent loss of groundwater storage capacity. Our results suggest that the long-term overexploitation has threatened the water supply security in Cangzhou. It is demonstrated that InSAR can be an effective tool for assessing the “physical state” and “sustainable development potential” of a confined aquifer system.

Evaluation of GRACE derived groundwater storage changes in different agro-ecological zones of the Indus Basin

The Gravity Recovery and Climate Experiment (GRACE) has recently been identified as a useful tool for monitoring changes in groundwater storage (GWS), especially in areas with sparse groundwater monitoring networks. However, GRACE's performance has not been evaluated in the highly heterogeneous Indus Basin (IB) to date. The objective of this study was thus (i) to evaluate GRACE's performance in two distinctively different agro-ecological zones of the IB, and (ii) to quantify the trend of groundwater abstraction over 15 years (i.e., from 2002 to 2017). To capture this heterogeneity at the IB, the two different agro-ecological zones were selected: i) the Kabul River Basin (KRB), Afghanistan, and ii) the Lower Bari Doab Canal (LBDC) command area in Pakistan. The groundwater storage anomalies (GWSA) for both regions were extracted from random pixels. The results show a correlation (R2) of 0.46 for LBDC and 0.32 for the KRB, between the GWSA and in-situ measurements. The results further reveal a mean annual depletion in GWSA of −304.2 ± 749 and −301 ± 527 mm at the LBDC and the KRB, respectively. Overall, a net GWS depletion during 2002–2017 at the LBDC and KRB was 4.87 and 4.82 m, respectively. The GWSA’s response to precipitation analyzed through cross-correlation shows a lag of 4 and 3 months at the KRB and the LBDC, respectively. The GWSA's poor correlation with the in-situ measurements particularly in the mountainous region of the KRB is driven by the 4 months lag time unlike in the LBDC (i.e. 3 months); besides, the observations wells are sparse and limited. The complex geomorphology and slope of the landscape also cause discrepancies in the correlation of the in-situ measurements and the GRACE-derived changes in GWS at the two different agroecological zones of the IB. The spatially averaged GWSA in monthly time steps is another reason for the lower correlation between GRACE-based GWSA estimates and point-based in-situ measurements. Therefore, care must be taken while using GRACE's output in regions with heterogeneous geomorphologic features.

Estimation of spatio-temporal groundwater storage variations in the Lower Transboundary Indus Basin using GRACE satellite

In the Lower Transboundary Indus Basin (LTIB), excessive groundwater is being consumed in combination with surface water to meet the increasing demand for irrigation and resulting in groundwater depletion. This study employed the generalized three-cornered hat method (GTCH) to assess uncertainty of different Gravity Recovery and Climate Experiment (GRACE) derived-terrestrial water storage anomalies (TWSA) measurements using GRACE (-TWSA) data and the variance variability in space and time of GRACE derived groundwater storage anomalies (GWSA) using Empirical Orthogonal Function (EOF) analysis, respectively. Furthermore, monthly GRACE derived GWSA were estimated using Global Land Data Assimilation System (GLDAS) model data and GWSA time series trend and depletion of groundwater storage were evaluated using the MannKendal (MK) trend test and Sen’s slope estimator in the LTIB. The TWSA and precipitation data depict seasonal characteristics with peaks in the summer and dips in the winter, which reflect variation in GWSA, respectively. Additionally, it is observed that the variations in GWSA exhibit a downward trend from 2003 to 2016. The results revealed that more than 80% of total variance variability was explained by the first 2 EOF modes. The results showed that GRACE derived GWSA is being depleted at a rate of 4.16 ± 0.26 mm per year (2.97 ± 0.19 km3 per year). Long-term monthly mean of GRACE derived GWSA showed remarkable agreements of correlation of determination (R2) with PCRaster Global Balance (PCR-GLOBWB) model 75% and WGHM (WaterGap Global Hydrological model) 81%. The GRACE-derived GWSA also showed a good correlation of 0.69 and 0.82 with in situ data on seasonal and annual scales, respectively. This study would be insightful to calculate the agro-economic impact of excessive groundwater withdrawal.

Predicting of the Climate-induced Depletion in Groundwater Level and Storage: A case in Akarçay Basin

In this study, we examined the potential impact of climate change on the depletion of groundwater levels and storage. To achieve so, we simulated the groundwater flow using the HİDROTÜRK hydrogeological model under the climate change projections considering the RCP4.5 and RCP8.5 scenarios. To estimate the model forcing input (recharge and evapotranspiration) for the hydrogeological model, we used precipitation and temperature outputs from two Global Circulation Models, namely HadGEM2-ES and MPI-ESM-MR. To assess the changes in groundwater level and storage, we applied our experimental design in the Şuhut alluvial aquifer in Akarçay Basin (Turkey). The study revealed that there is not necessarily a substantial difference tracked over the estimated groundwater levels between the RCP4.5 and RCP8.5 scenarios until the end of 2050s. Yet, a significant reduction in the hydraulic head (approximately 114 m) and storage change (-17.25 %) – particularly in the western part of the aquifer – is expected in 2100, according to RCP8.5. This study confirmed that the selected climate model not only leads to the different predictions in the groundwater depletion, yet also results in a different degree of confidence in the model simulations.

Combining GRACE and satellite altimetry data to detect change in sediment load to the Bohai Sea

The Gravity Recovery and Climate Experiment (GRACE) satellites provide a powerful tool for monitoring sediment mass change. However, signal leakage from nearby groundwater storage depletion in the North China Plain limits the potential capacity of GRACE to estimate sediment input from the Yellow River flows into the Bohai Sea. In the present work, we developed an improved approach based on forward modeling to reduce signal leakage from GRACE data and combined it with satellite altimetry to recover sediment load changes from 2003 to 2013 to the Bohai Sea. The total sediment input averaged 1.7 ± 0.8 Gt/yr, which agrees well with the estimate based on in-situ sediment data measured from the sediment cores (1.1 Gt/yr). Our method is also capable to describe sediment seasonal variations, with higher inputs in winter and spring, which confirm the output simulated by the sediment transportation model. We make presently tentative connections of seasonal variations to sediment resuspension driven by climatic monsoons contributed rough seas: although sediment load in rivers peaks in summer, low water discharge of the Yellow River leads to most of the sediment being deposited in a narrow area near the river mouth and not transported into the Bohai Sea; in winter and spring, huge waves provide favorable conditions for resuspension resulting in large amounts of sediment near the estuary being transported to the ocean along with northward waves. Moreover, our results indicate coastal erosion is also a nonnegligible resource of the sediment in the Bohai Sea. Comparing to the traditional approach, our study provides a new technological way to derive sediment in the Bohai Sea, which is capable of providing continuous measurements with improved timeliness at a lower cost.

Impacts of water resources management on land water storage in the North China Plain: Insights from multi-mission earth observations

Natural conditions of surface water bodies and groundwater aquifers in the North China Plain (NCP) have been altered to meet the ever-growing human water demands. Several water resources management measures have been implemented in recent decades to alleviate groundwater depletion, maintain ecological resilience, and sustain agricultural production. This study aims to investigate their impacts on land water storage, and thus obtain a picture of the spatio-temporal variation of water resources over the NCP. Based on multi-mission earth observation datasets, i.e., altimetry (Sentinel-3), synthetic aperture radar (SAR) and spectral imagery (Sentinel-1/2), gravimetry (GRACE/-FO), and microwave sensors (IMERG), as well as reanalysis datasets, we investigate surface water storage (SWS), soil moisture water storage (SMS), and total water storage (TWS) changes. Groundwater storage (GWS) change is subsequently estimated as the residual of the total storage equation.Results show that TWS declined significantly over the past decades (−1.04 ± 0.05 cm/yr in 2004 to 2020), while SMS rebounded after a decreasing trend from 2004 to 2014. The spatial pattern of TWS variations depicts a particularly severe depletion along provincial boundaries. The SWS dynamics reveal that the volumes of three major NCP reservoirs (Guanting, Miyun, and Danjiangkou) increased significantly since around 2014 when the operation of the South-to-North Water Diversion Middle Route project (SNWDP-MR) started. Moreover, GWS maintained a depletion rate of −1.05 ± 0.08 cm/yr during 2004–2014 over the whole NCP, while the depletion rate accelerated during 2015–2020 (−1.88 ± 0.38 cm/yr). We also found that the GWS depletion in Beijing (−1.20 ± 0.10 cm/yr during 2004–2014 and −0.79 ± 0.44 cm/yr during 2015–2020) and its surrounding areas has been lowered possibly because of the SNWDP-MR. This study shows how multi-mission satellite earth observation products can be combined to monitor water resources at a regional scale and provide spatio-temporally resolved estimates of the impacts of human-induced changes in the inland water cycle.

Impact of Groundwater Abstraction on Hydrological Responses during Extreme Drought Periods in the Boryeong Dam Catchment, Korea

Groundwater withdrawal results in a significant depletion of groundwater storage due to the frequency and intensity of droughts and increasing irrigation demands. To ensure the sustainable use of groundwater resources, it is necessary to accurately simulate the groundwater behavior of catchments using a surface–groundwater integrated runoff model. Most of the existing catchment runoff models have been applied to surface water management; thus, integrated runoff analysis studies that consider the interaction between surface water and groundwater are required. Due to the intensive agricultural sector in Korea and the position of rice as the staple in the Korean diet, more than 50% of groundwater abstraction is used for irrigation. Therefore, it is very important to understand the hydrological interrelationships between agricultural areas and the entire watershed. This study aimed to compare and analyze the groundwater levels in the mountainous areas and paddy field areas in the Boryeong Dam catchment through a surface–groundwater integrated runoff simulation using the Catchment Hydrologic Cycle Assessment Tool model, and to compare the hydrological responses in wet years (2010–2012) and dry years (2014–2016). The maximum difference in the monthly groundwater level in the dry years compared to the wet years was 1.07 m at the forest catchment and 0.37 m at the paddy catchment. These results indicate that the impact of drought on the groundwater level of paddy catchments is not significant compared to the forest catchments; however, drought slows the recovery of the groundwater level before the rainy season, thereby limiting the agricultural groundwater use in the catchment.

Spatio-temporal variations in stable isotopes in peri-urban catchments: A preliminary assessment of potential and challenges in assessing streamflow sources

In peri-urban catchments where treated wastewater effluents are released into surface waters, knowledge of water sources and partitioning is important for mitigating water quality impacts, particularly during warm and dry periods with low discharge rates. Useful tools for the identification of water sources and flow paths under different wetness conditions are isotope tracers. However, very few studies have been carried out so far in urbanized catchments with complex land use distributions where natural headwaters interact with engineered components, e.g. effluent discharge. We undertook spatio-temporal sampling of isotopes, combined with water quality measurements, to complement climatic and hydrometric data across the 220 km2 peri-urban Erpe catchment near Berlin and assess seasonal changes in water sources during two exceptionally warm and dry years (2018 and 2019). The study showed a deterioration of water quality downstream of two municipal wastewater treatment plants; and the depletion of groundwater storage, along with isotopic enrichment of the stream, in summer 2019 (the second consecutive year with above-average temperatures and marked precipitation deficits). Streamflow in the upper reaches of the catchment was dominated by groundwater-fed tributaries in winter, but became increasingly dominated by wastewater in summer. In the lower catchment, flows were dominated by effluent from a large wastewater treatment plant, especially in summer. Young water from precipitation and urban storm runoff accounted for < 10 % of streamflow, despite the catchment being ~ 20 % urban. Similarities in the composition of wastewater and other runoff sources resulted in high uncertainties in end member separation and highlight the need for monitoring of other tracers to better characterize water impacts. Given climate change projections for the region are for drier, warmer summers, wastewater is likely to become a more dominant component of streams, which may have implications for environmental quality and ecosystem services.

Sub-regional groundwater storage recovery in North China Plain after the South-to-North water diversion project

The South-to-North water diversion Middle Route Project (MRP) is expected to alleviate the long-term groundwater storage (GWS) depletion in North China Plain (NCP) after the beginning of its operation in December 2014. This study aims to investigate the effect of MRP on GWS by comparing GWS changes before (2003–2014) and after (2015–2018) the MRP operation. The analysis was conducted by using groundwater level data from 617 wells in NCP, and then evaluated against satellite-based water storage data from Gravity Recovery and Climate Experiment (GRACE) and its Follow-On missions. On average in NCP, a decreasing trend of −19.1 ± 5.1 mm/yr was seen in GWS based on well observations during 2003–2014, but a recovery trend of +1.8 ± 0.7 mm/yr was found during 2015–2018. The GWS recovery was most prominent in subregions where groundwater over-utilization had occurred in NCP. GRACE exhibited the capacity to detect the regional GWS depletion during 2003–2014, but difficult to distinguish the sub-regional GWS recovery during 2015–2018. The potential causes for GWS recovery were found to be complicated, not only caused by the reduction of groundwater pumping as accelerated by MRP-diverted water, but also the increasing precipitation recharge of aquifers and the enhanced management of groundwater system. The findings highlight that GWS in NCP has started a gradual transition from unsustainable depletion to sub-regional recovery as benefit from the MRP water diversion.

Comparison of Groundwater Storage Changes From GRACE Satellites With Monitoring and Modeling of Major U.S. Aquifers

AbstractGRACE satellite data are widely used to estimate groundwater storage (GWS) changes in aquifers globally; however, comparisons with GW monitoring and modeling data are limited. Here we compared GWS changes from GRACE over 15 yr (2002–2017) in 14 major U.S. aquifers with groundwater‐level (GWL) monitoring data in ~23,000 wells and with regional and global hydrologic and land surface models. Results show declining GWS trends from GRACE data in the six southwestern and south‐central U.S. aquifers, totaling −90 km3 over 15 yr, related to long‐term (5–15 yr) droughts, and exceeding Lake Mead volume by ~2.5×. GWS trends in most remaining aquifers were stable or slightly rising. GRACE‐derived GWS changes agree with GWL monitoring data in most aquifers (correlation coefficients, R = 0.52–0.95), showing that GRACE satellites capture groundwater (GW) dynamics. Regional GW models (eight models) generally show similar or greater GWS trends than those from GRACE. Large discrepancies in the Mississippi Embayment aquifer, with modeled GWS decline approximately four times that of GRACE, may reflect uncertainties in model storage parameters, stream capture, pumpage, and/or recharge rates. Global hydrologic models (2003–2014), which include GW pumping, generally overestimate GRACE GWS depletion (total: approximately −172 to −186 km3) in heavily exploited aquifers in southwestern and south‐central U.S. by ~2.4× (GRACE: −74 km3), underscoring needed modeling improvements relative to anthropogenic impacts. Global land surface models tend to track GRACE GWS dynamics better than global hydrologic models. Intercomparing remote sensing, monitoring, and modeling data underscores the importance of considering all data sources to constrain GWS uncertainties.

Spatio-Temporal Variations in Groundwater Revealed by GRACE and Its Driving Factors in the Huang-Huai-Hai Plain, China.

The Huang-Huai-Hai (3H) Plain is the major crop-producing region in China. Due to the long-term overexploitation of groundwater for irrigation, the groundwater funnel is constantly expanding and the scarcity of water resources is prominent in this region. In this study, Gravity Recovery and Climate Experiment (GRACE) and hydrological models were used to estimate the spatial-temporal changes of groundwater storage (GWS) and the driving factors of GWS variations were discussed in the 3H Plain. The results showed that GRACE-based GWS was depleted at a rate of −1.14 ± 0.89 cm/y in the 3H Plain during 2003 to 2015. The maximum negative anomaly occurred in spring due to agricultural irrigation activities. Spatially, the loss of GWS in the Haihe River Basin is more serious than that in the Huaihe River Basin, presenting a decreasing trend from south to north. Conversely, the blue water footprint (WFblue) of wheat exhibited an increasing trend from south to north. During the drought years of 2006, 2013, and 2014, more groundwater was extracted to offset the surface water shortage, leading to an accelerated decline in GWS. This study demonstrated that GWS depletion in the 3H Plain is well explained by reduced precipitation and groundwater abstraction due to anthropogenic irrigation activities.

Planning for groundwater sustainable use: A case study in Nishapur Plain, Iran

In Iran, due to arid and semi-arid climate, groundwater resources play an essential role in food production, as well as domestic and industrial water supply. In recent years, increasing population, scarcity of surface water resources, and effects of worldwide and regional climate change have resulted in over-exploitation and unsustainability of these resources in the country. The present study aims to estimate groundwater sustainable yield, examine effects of spatial and temporal scale, and propose a plan for groundwater sustainable use in Nishapur Plain, in the north-east of Iran. In investigating the effects of spatial scale, the area of the plain is divided into several zones, with estimation of groundwater recharge and discharge for each zone and the temporal scale refers to the different time-scales used to estimate the average value of groundwater recharge and discharge. The results of the transient groundwater model of Nishapur Plain, revealed that average annual groundwater storage depletion is about 311 MCM11Million Cubic Meters during the 8-year period of 2005–2013 with the minimum, average, and maximum water table decline of 0.6 m, 7.7 m and 11 m, respectively. The study results suggest that sustainable yield is closely correlated to the spatial and temporal scales, and refinement of spatial and temporal scales increases sustainable yield from 39 % to 59 % of the current pumping volume equal to about 100 MCM of water (or 8000 ha of irrigated land). Furthermore, when the groundwater withdrawals are limited to sustainable yield, increasing irrigation efficiency from 38 % (current efficiency) to about 60 %, can potentially result in maintaining irrigated areas and minimize adverse social and economic impacts of limiting groundwater usage. This is an achievable rate, based on data from the Iranian government organizations. The results of this study can be extended to other semi-arid agricultural areas, which primarily depend on groundwater.

Analysis of Groundwater and Total Water Storage Changes in Poland Using GRACE Observations, In-situ Data, and Various Assimilation and Climate Models

The Gravity Recovery and Climate Experiment (GRACE) observations have provided global observations of total water storage (TWS) changes at monthly intervals for over 15 years, which can be useful for estimating changes in GWS after extracting other water storage components. In this study, we analyzed the TWS and groundwater storage (GWS) variations of the main Polish basins, the Vistula and the Odra, using GRACE observations, in-situ data, GLDAS (Global Land Data Assimilation System) hydrological models, and CMIP5 (the World Climate Research Programme’s Coupled Model Intercomparison Project Phase 5) climate data. The research was conducted for the period between September 2006 and October 2015. The TWS data were taken directly from GRACE measurements and also computed from four GLDAS (VIC, CLM, MOSAIC, and NOAH) and six CMIP5 (FGOALS-g2, GFDL-ESM2G, GISS-E2-H, inmcm4, MIROC5, and MPI-ESM-LR) models. The GWS data were obtained by subtracting the model TWS from the GRACE TWS. The resulting GWS values were compared with in-situ well measurements calibrated using porosity coefficients. For each time series, the trends, spectra, amplitudes, and seasonal components were computed and analyzed. The results suggest that in Poland there has been generally no major TWS or GWS depletion. Our results indicate that when comparing TWS values, better compliance with GRACE data was obtained for GLDAS than for CMIP5 models. However, the GWS analysis showed better consistency of climate models with the well results. The results can contribute toward selection of an appropriate model that, in combination with global GRACE observations, would provide information on groundwater changes in regions with limited or inaccurate ground measurements.

Characterization of the Groundwater Storage Systems of South-Central Chile: An Approach Based on Recession Flow Analysis

Groundwater storage and discharge are important processes that have not yet been sufficiently studied in some parts of Chile. Additionally, in watersheds without snow cover or glaciers, groundwater storage and release are the main sources of minimum flow generation; therefore, improvements are required to characterize this process. This study aimed to use recession flow analysis to link groundwater storage depletion to the predominant geological characteristics of each watershed in order to improve our understanding of the groundwater storage-release process in 24 watersheds in south-central Chile. The results allowed different groundwater storage behaviors associated with different geological characteristics to be identified, making recession flow analysis a valuable tool for improving the representation and conceptualization of this process in order to advance toward better minimum flow predictions.

Multi-hazard Groundwater Risks to Water Supply from Shallow Depths: Challenges to Achieving the Sustainable Development Goals in Bangladesh

Groundwater currently provides 98% of all drinking-water supply in Bangladesh. Groundwater is found throughout Bangladesh but its quality (i.e., arsenic and salinity contamination) and quantity (i.e., water-storage depletion) vary across hydrological environments, posing unique challenges to certain geographical areas and population groups. Yet, no national-scale, multi-parameter groundwater hazard maps currently exist enabling water resources managers and policy makers to identify vulnerable areas to public health. We develop, for the first time, groundwater multi-hazard maps at the national scale of Bangladesh combining information on arsenic, salinity, and water storage. We apply geospatial techniques in ‘R’ programming language and ArcGIS environment, linking hydrological indicators for water quality and quantity to construct risk maps. A range of socioeconomic variables including access to drinking and irrigation water supplies and social vulnerability (i.e., poverty) are overlaid on these risk maps to estimate exposures. Our multi-parameter groundwater hazard maps show that a considerable proportion of land area (5–24% under extremely high to high risks) in Bangladesh is currently under combined risk of arsenic and salinity contamination, and groundwater-storage depletion. As small as 6.5 million (2.2 million poor) to 24.4 million (8.6 million poor) people are exposed to a combined risk of high arsenic, salinity, and groundwater-storage depletion. Our groundwater hazard maps reveal areas and exposure of population groups to water risks posed by arsenic and salinity contamination and depletion of water storage. These geospatial hazard maps can potentially guide policy makers in prioritizing mitigation and adaptation measures in order to achieve the United Nation’s Sustainable Development Goals across the water, agriculture, and public health sectors in Bangladesh.