Groundwater Storage Anomalies Research Articles

Subregional‐scale groundwater depletion detected by GRACE for both shallow and deep aquifers in North China Plain

AbstractThis 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).

Groundwater storage variability and annual recharge using well-hydrograph and GRACE satellite data

Most studies using GRACE (Gravity Recovery and Climate Experiment) data for examining water storage anomalies have rich hydrogeological databases. Here, GRACE data are analyzed for southern Mali, Africa, a region with sparse hydrogeological data. GRACE data (2002–2008) did not overlap with observed groundwater-level data (1982–2002). Terrestrial water storage from GRACE was corrected for soil moisture using the Global Land Data Assimilation System (GLDAS) model to obtain monthly groundwater storage anomalies and annual net recharge. Historical storage anomalies and net recharge were determined using the water-table fluctuation method for available observation wells. Average annual net recharge averaged 149.1 mm (or 16.4% of annual rainfall) and 149.7 mm (14.8%) from historical water level and GRACE data, respectively. Monthly storage anomaly lows and peaks were observed in May and September, respectively, but have a shift in peak to November using the corrected GRACE data, suggesting that the GLDAS model may poorly predict the timing of soil-water storage in this region. Notwithstanding problems with the GLDAS model, the soil moisture-corrected GRACE data accurately predict the relative timing and magnitude of groundwater-storage changes, suggesting that GRACE data are valuable for identifying long-term regional changes in groundwater storage in areas with sparse hydrogeological data.

Estimating groundwater storage changes in the Mississippi River basin (USA) using GRACE

Based on satellite observations of Earth’s time variable gravity field from the Gravity Recovery and Climate Experiment (GRACE), it is possible to derive variations in terrestrial water storage, which includes groundwater, soil moisture, and snow. Given auxiliary information on the latter two, one can estimate groundwater storage variations. GRACE may be the only hope for groundwater depletion assessments in data-poor regions of the world. In this study, soil moisture and snow were simulated by the Global Land Data Assimilation System (GLDAS) and used to isolate groundwater storage anomalies from GRACE water storage data for the Mississippi River basin and its four major sub-basins. Results were evaluated using water level records from 58 wells set in the unconfined aquifers of the basin. Uncertainty in the technique was also assessed. The GRACE-GLDAS estimates compared favorably with the well based time series for the Mississippi River basin and the two sub-basins that are larger than 900,000 km2. The technique performed poorly for the two sub-basins that have areas of approximately 500,000 km2. Continuing enhancement of the GRACE processing methods is likely to improve the skill of the technique in the future, while also increasing the temporal resolution.