Improved methods for satellite-based groundwater storage estimates: A decade of monitoring the high plains aquifer from space and ground observations

The impacts of climate extremes and water use on groundwater storage across large aquifers can be quantified using Gravity Recovery and Climate Experiment (GRACE) satellite monitoring. We present new methods to improve estimates of changes in groundwater storage by incorporating irrigation soil moisture corrections to common data assimilation products. These methods are demonstrated using data from the High Plains Aquifer (HPA) for 2003 to 2013. Accounting for the impacts of observed and inferred irrigation on soil moisture significantly improves estimates of groundwater storage changes as verified by interpolated measurements from ~10,000 HPA wells. The resulting estimates show persistent declines in groundwater storage across the HPA, more severe in the southern and central HPA than in the north. Groundwater levels declined by an average of approximately 276 ± 23 mm from 2003 to 2013, resulting in a storage loss of 125 ± 4.3 km3, based on the most accurate of the three methods developed here. Key Points Irrigation should be included in satellite‐based groundwater storage studiesGroundwater storage across the HPA declined by 78 to 125 km3 since 2003Uncertainty in groundwater depletion must be addressed in future GRACE studies