Monitoring seasonal groundwater storage anomalies using remote sensing

Gravity Recovery and Climate Experiment (GRACE) satellite mission is ground-breaking information hotspot for the evaluation of groundwater storage. The present study aims at validating the sensitivity of GRACE data to groundwater storage variation within a basaltic aquifer system after its statistical downscaling on a regional scale. The basaltic aquifer system which covers 82.06% area of Maharashtra state in India, is selected as the study area. Five types of basaltic aquifer systems with varying groundwater storage capacities, based on hydrologic characteristics, have been identified within the study area. The spatial and seasonal trend analysis of observed in situ groundwater storage anomalies (ΔGWSano) computed from groundwater level data of 983 wells from the year 2002 to 2016, has been performed to analyze the variation in groundwater storages in the different basaltic aquifer system. The groundwater storage anomalies (ΔGWSDano) have been derived from GRACE Release 05 (RL05) after removing the soil moisture anomaly (ΔSMano) and canopy water storage anomaly (ΔCNOano) obtained from Global Land Data Assimilation System (GLDAS) land surface models (NOAH, MOSAIC, CLM and VIC). The artificial neural network technique has been used to downscale the GRACE and GLDAS data at a finer spatial resolution of 0.125°. The study shows that downscaled GRACE and GLDAS data at a finer spatial resolution is sensitive to seasonal groundwater storage variability in different basaltic aquifer systems and the regression coefficient R has been found satisfactory in the range of 0.696 to 0.818.

In the era of global climate change, the monitoring of water resources, including groundwater, is of fundamental importance for nature, agriculture, economy and society. The purpose of this paper is to check compliance of changes in groundwater level obtained from direct measurements in wells with groundwater storage (GWS) anomalies calculated using gravity recovery and climate experiment (GRACE) observations in Poland. Data from the global land data assimilation (GLDAS), in the form of soil moisture (SM) and snow water equivalence (SWE), were used to convert GRACE observations into a series of GWS changes. It was found that very high consistency occurs between GRACE observations and changes in water level in wells, while the GWS series obtained from GRACE and GLDAS do not provide adequate compatibility. Further research presented in the paper was devoted to attempts to explain this phenomenon. In addition, time series of GRACE, GLDAS and groundwater head series were analyzed.

This study explores the capability of Gravity Recovery and Climate Experiment (GRACE) to detect heterogeneous groundwater storage (GWS) variations in two subregions of the North China Plain: the Piedmont Plain (PP, ~54,000 km2, mainly exploiting shallow groundwater) and East Central Plain (ECP, ~86,000 km2, mainly exploiting deep groundwater). Results show that the GWS anomalies estimated from GRACE data (2003–2013) agree well with those estimated from in situ observations (2005–2010) for both PP (R2 = 0.91) and ECP (R2 = 0.75). The shallow GWS (2003–2013) in PP declines faster (−46.5 ± 6.8 mm/yr) than the deep GWS in ECP (−16.9 ± 1.9 mm/yr). However, the shallow GWS in PP recovered more quickly especially during the 2008–2011 drought period. Despite its lower magnitude, the GRACE‐derived GWS depletion in ECP reveals the overexploitation of deep GWS. This study demonstrated that the heterogeneous GWS variations can potentially be detected by GRACE at the subregional scale smaller than the typical GRACE footprint (200,000 km2).

<p>Climate change increases the probability of drought occurrence in many parts of the United States and worldwide. Aquifer response to these drought events vary in space and time. This project seeks to understand the response of aquifers to drought events by quantifying the lag time between meteorological droughts and groundwater droughts using the Standardized Precipitation and Evapotranspiration Index (SPEI) and Gravity Recovery and Climate Experiment (GRACE) derived groundwater storage anomalies. Ten major aquifer systems in the continental United States were selected for analysis: Columbia Plateau, Arizona Alluvial, Snake River Basin, Upper Colorado, Pennsylvanian, Mississippi Embayment, Texas Gulf Coast, Edwards-Trinity Plateau, Floridian, Central California, and the High Plains Aquifer Systems. Groundwater storage anomaly data was derived from GRACE total water storage anomaly data by removing all other hydrologic components using the Global Land Data Assimilation System’s (GLDAS) Community Land Surface Model (CLM) of 1.0-degree spatial resolution monthly datasets. Timeseries on monthly intervals for both the derived groundwater storage and SPEI were created for the period of April 2002 to June 2021. Each selected aquifer system had a meteorological drought occur at least three times during the study period, with a maximum occurrence of fifteen in central California. There is a temporal gap in between the original GRACE mission and the launch of GRACE-Follow on (GRACE-FO) from June 2017 to June 2018, five of the ten selected aquifers had meteorological droughts occur in this gap, which have been excluded. Preliminary results indicate that the lag time between the start of the two types of droughts for these aquifer systems is between zero and one month, while the lag time between the end of these types of droughts is more widely varied, between zero and eight months. As these results are varied, contextualizing them with more in-depth looks at the aquifer system characteristics is important and is the next step in furthering our understanding of aquifer responses to the increasing number of probable drought events.</p>

The water‐receiving area of the South‐to‐North Water Diversion Eastern Route Project (SNWDP‐ER) is one of the most severely affected water‐shortage areas in China, and no previous study has been conducted on the changes in water storage in this area. In this study, we combined the latest Gravity Recovery and Climate Experiment (GRACE) And GRACE Follow‐On products with global models for the first time to analyze changes in water storages in this area from 2002 to 2020, and to investigate the effects of climate change and human activity on changes in water storage. We found that SNWDP‐ER aided the recovery of surface water (nongroundwater) with a recovery rate of 9.44 ± 1.65 mm/yr after its implementation, but had little effect on the recovery of groundwater and terrestrial water storage in the water‐receiving area. Before the SNWDP‐ER was implemented, the rates of decrease of groundwater and terrestrial water storage were only −1.59 ± 0.58 and −5.18 ± 0.75 mm/yr, respectively. After implementation, the rates of decrease of groundwater and terrestrial water storage were −17.7 ± 1.27 and −8.16 ± 1.18 mm/yr, respectively. Groundwater decline, accelerated by human activity and climate change, has led to an accelerated decline in terrestrial water storage. Effects of SNWDP‐ER and stringent policies reducing groundwater use, along with largely increased precipitation in North China on groundwater storage after year 2020 need to be examined in the future. Our results have important implications for the management and evaluation of SNWDP‐ER.

Groundwater is crucial for economic development in arid and semiarid areas. The Shiyang River Basin (SRB) has the most prominent water use issues in northwestern China, and overexploited groundwater resources have led to continuous groundwater-level decline. The key governance planning project of the SRB was issued in 2007. This paper synthetically combines remote-sensing data from Gravity Recovery and Climate Experiment (GRACE) data and precipitation, actual evapotranspiration, land use, and in situ groundwater-level data to evaluate groundwater storage variations on a regional scale. Terrestrial water storage anomalies (TWSA) and groundwater storage anomalies (GWSA), in addition to their influencing factors in the SRB since the implementation of the key governance project, are analyzed in order to evaluate the effect of governance. The results show that GRACE-derived GWS variations are consistent with in situ observation data in the basin, with a correlation coefficient of 0.68. The GWS in the SRB had a slow downward trend from 2003 to 2016, and this increased by 0.38 billion m³/year after 2018. As the meteorological data did not change significantly, the changes in water storage are mainly caused by human activities, which are estimated by using the principle of water balance. The decline in GWS in the middle and lower reaches of the SRB has been curbed since 2009 and has gradually rebounded since 2014. GWS decreased by 2.2 mm EWH (equivalent water height) from 2011 to 2016, which was 91% lower than that from 2007 to 2010. The cropland area in the middle and lower reaches of the SRB also stopped increasing after 2011 and gradually decreased after 2014, while the area of natural vegetation gradually increased, indicating that the groundwater level and associated ecology significantly recovered after the implementation of the project.

Long-term and seasonal variation in groundwater storage in the North China Plain based on GRACE

Amidst changing climates, understanding the world’s water resources is of increasing importance. In Ontario, Canada, low water conditions are currently assessed using only precipitation and watershed-based stream gauges by the Conservation Authorities in Ontario and the Ministry of Natural Resources and Forestry. Regional groundwater-storage changes in Ontario are not currently measured using satellite data by research institutes. In this study, contributions from the Gravity Recovery and Climate Experiment (GRACE) data are compared to a hydrogeological database covering southern Ontario from 2003 to 2013, to determine the suitability of GRACE total water storage estimates for monitoring groundwater storage in this location. Terrestrial water storage data from GRACE were used to determine monthly groundwater storage (GWS) anomaly values. GWS values were also determined by multiplying groundwater-level elevations (from the Provincial Groundwater Monitoring Network wells) by specific yield. Comparisons of GRACE-derived GWS to well-based GWS data determined that GRACE is sufficiently sensitive to obtain a meaningful signal in southern Ontario. Results show that GWS values produced by GRACE are useful for identifying regional changes in groundwater storage in areas with limited available hydrogeological characterization data. Results also indicate that GRACE may have an ability to forecast changes in groundwater storage, which will become useful when monitoring climate shifts in the near future.

Long-term groundwater variations in Northwest India from satellite gravity measurements

Optimizing GRACE/GRACE-FO data and a priori hydrological knowledge for improved global terrestial water storage component estimates

Abstract. Accurate estimation of terrestrial water storage (TWS) at a high spatiotemporal resolution is important for reliable assessments of regional water resources and climate variability. Individual components of TWS include soil moisture, snow, groundwater, and canopy storage and can be estimated from the Community Atmosphere Biosphere Land Exchange (CABLE) land surface model. The spatial resolution of CABLE is currently limited to 0.5∘ by the resolution of soil and vegetation data sets that underlie model parameterizations, posing a challenge to using CABLE for hydrological applications at a local scale. This study aims to improve the spatial detail (from 0.5 to 0.05∘) and time span (1981–2012) of CABLE TWS estimates using rederived model parameters and high-resolution meteorological forcing. In addition, TWS observations derived from the Gravity Recovery and Climate Experiment (GRACE) satellite mission are assimilated into CABLE to improve TWS accuracy. The success of the approach is demonstrated in Australia, where multiple ground observation networks are available for validation. The evaluation process is conducted using four different case studies that employ different model spatial resolutions and include or omit GRACE data assimilation (DA). We find that the CABLE 0.05∘ developed here improves TWS estimates in terms of accuracy, spatial resolution, and long-term water resource assessment reliability. The inclusion of GRACE DA increases the accuracy of groundwater storage (GWS) estimates and has little impact on surface soil moisture or evapotranspiration. Using improved model parameters and improved state estimations (via GRACE DA) together is recommended to achieve the best GWS accuracy. The workflow elaborated on in this paper relies only on publicly accessible global data sets, allowing the reproduction of the 0.05∘ TWS estimates in any study region.

Recently, the worldwide drought situation has gotten worse and is posing a serious threat to many nations, including Iraq. It is now unavoidable to use modern technologies, including remote sensing, to lessen the effects of this catastrophe. This paper aims to check the consistency of groundwater storage (GWS) derived from multiple sources utilizing remote sensing data with direct measurements in wells in the Dammam unconfined aquifer, which is situated in Al-Muthanna Governorate, Iraq. This study utilizes the water-level readings from well records from January 2008 to December 2014. The groundwater results from different combinations of Gravity Recovery and Climate Experiment (GRACE) products, Goddard Space Flight Center (GSFC) mascon, Jet Propulsion Laboratory Downscaled (JPLD), and Catchment Land Surface Model (CLSM), are calibrated and validated using statistical analysis. The findings illustrate large GWS depletion rates of GWS_W, GWS_JPLD, and GWS_GSFC at -54∓10 mm/yr, -11∓5 mm/yr, -6∓5 mm/yr, respectively. The Pearson, Spearman, and Kendall correlation reaches 0.93, 0.96, and 0.90 with a P-value less than 0.05. The highest coefficient of determination (R2) was 0.93 for GWS_GSFC, and the lowest was 0.42 for GWS_JPLD. The finding of classification of the GSFC and JPL data indicated that the GWS agrees with the spatial and temporal distributions of the highest depletion in the Dammam Aquifer. The study demonstrated that GRACE estimations can accurately reflect monthly variations in groundwater stocks, making them a valuable tool for resource managers to assess the water situation and plan sustainable water use.

Balancing groundwater supply and food production is challenging, especially in large regions where there is often insufficient information on the groundwater budget, such as in the North China Plain (NCP) and the Northeast China Plain (NECP), which are major food producing areas in China. This study aimed to understand this process in a simple but efficient way by using Gravity Recovery and Climate Experiment (GRACE) data, and it focused on historical and projected groundwater storage (GWS) changes in response to changes in grain-sown areas. The results showed that during 2003–2016, the GWS was depleted in the NCP at a rate of −17.2 ± 0.8 mm/yr despite a decrease in groundwater abstraction along with an increase in food production and a stable sown area, while in the NECP, the GWS increased by 2.3 ± 0.7 mm/yr and the groundwater abstraction, food production and the sown area also increased. The scenario simulation using GRACE-derived GWS anomalies during 2003–2016 as the baseline showed that the GWS changes in the NCP can be balanced (i.e., no decreasing trend in storage) by reducing the area of winter wheat and maize by 1.31 × 106 ha and 3.21 × 106 ha, respectively, or by reducing both by 0.93 × 106 ha. In the NECP, the groundwater can sustain an additional area of 0.62 × 106 ha of maize without a decrease in storage. The results also revealed that the current groundwater management policies cannot facilitate the recovery of the GWS in the NCP unless the sown ratio of drought-resistance wheat is increased from 90% to 95%. This study highlights the effectiveness of using GRACE to understanding the nexus between groundwater supply and food production at large scales.

Satellite-based remote sensing has become an extremely powerful technique for groundwater (GW) studies. We therefore examined the possible use of the gravity recovery and climate experiment (GRACE) data for estimating groundwater storage (GWS) changes in the Chicot Aquifer and across Louisiana State. The objectives of the study were to derive estimates of GWS changes from the GRACE data, validate the GRACE data using observational estimates, and assess its relationship with salinity changes in GW. GWS changes were estimated from GRACE and outputs of the North American Land Data Assimilation System (NLDAS) data sets. They were then compared against GWS changes derived from observed GW levels. The comparison shows a reasonable agreement with the trends of declining GW levels from 2002 to 2013. The correlation coefficient for the state of Louisiana was R = 0.62, whereas the correlation for the Chicot Aquifer was R = 0.31. However, the latter value improved through spatial resampling to a correlation of R = 0.81. The GWS changes were also compared with changes in salinity, showing strong correlations between GW depletion and increasing salinity. The GRACE/NLDAS data sets, along with the application of geographic information system techniques, can be used to monitor GW changes in regions where GW information is limited.

The West Liaohe River Basin (WLRB) is one of the most sensitive areas to climate change in China and an important grain production base in the Inner Mongolia Autonomous Region of China. Groundwater depletion in this region is becoming a critical issue. Here, we used the Gravity Recovery and Climate Experiment (GRACE) satellite data and in situ well observations to estimate groundwater storage (GWS) variations and discussed the driving factors of GWS changes in the WLRB. GRACE detects a GWS decline rate of −0.92 ± 0.49 km3/yr in the WLRB during 2005–2011, consistent with the estimate from in situ observations (−0.96 ± 0.19 km3/yr). This long-term GWS depletion is attributed to reduced precipitation and extensive groundwater overexploitation in the 2000s. Long-term groundwater level observations and reconstructed total water storage variations since 1980 show favorable agreement with precipitation anomalies at interannual timescales, both of which are significantly influenced by the El Niño-Southern Oscillation (ENSO). Generally, the WLRB receives more/less precipitation during the El Niño/La Niña periods. One of the strongest El Niño events on record in 1997–1998 and a subsequent strong La Niña drastically transform the climate of WLRB into a decade-long drought period, and accelerate the groundwater depletion in the WLRB after 1998. This study demonstrates the significance of integrating satellite observations, ground-based measurements, and climatological data for interpreting regional GWS changes from a long-term perspective.