Water scarcity is a critical issue in semiarid regions; however, regional groundwater monitoring is extremely limited. This study evaluates the ability of the GRACE satellite to monitor groundwater storage in the semiarid High Plains aquifer, USA (450,000 km2 area), which is subjected to intense irrigation. The GRACE satellite was launched in 2002 and provides monthly data on gravity at ~ 200,000 km2 resolution. GRACE-derived terrestrial water storage (TWS) is highly correlated with the sum of soil moisture (SM) and groundwater storage (GWS) (r = 0.90 for in-situ measured SM [90 stations], r = 0.91 for simulated SM with a land surface model) in the High Plains. Correlation between GWS changes calculated as GRACE TWS-SM and measured GWS [~1000 wells] is also high (r = 0.74 for in-situ SM, r = 0.79 for simulated SM). Variability in SM is mostly restricted to the upper 2 m of the soil. Monitored SM compared favorably with simulated SM (r = 0.82). Study results show the potential for using GRACE gravity measurements to monitor TWS and GWS over large semiarid regions subjected to intense irrigation.

Current studies by Laurent Longuevergne using GRACE are focusing on application of GRACE data to assessment of the 10 d solution for GRACE and comparison with the monthly solution in the Baltic Sea area where dynamic changes are occurring, application of GRACE to monitor declines in groundwater storage in the North China Plain, and evaluation of assimilation of GRACE data to water balance models using data from the Amazon. These studies are funded by NASA with supplemental funding from the Jackson School.