Groundwater Storage Changes in the United States using Baseflow Recession Method: Comparison with GRACE, and Observation Well Data

Groundwater is a major source of water supply over most regions, accounting for nearly one-third of all water abstraction globally. However, due to overreliance on this resource, many aquifers around the United States have experienced rapid depletion, while some aquifers have seen increasing water levels due to extensive recharge efforts. It is essential to have a comprehensive understanding of the rate at which groundwater storages are changing to assess the potential availability of groundwater in the future. In this work, we estimate groundwater storage changes across more than 1000 watersheds over the US from a proposed algorithm for baseflow extracted using streamflow and precipitation observations. We also study the spatial and temporal variations in the characteristic of baseflow recession. We compare the storage change estimated from baseflows with those obtained from the estimates from the Gravity Recovery and Climate Experiment (GRACE) and observations from monitoring wells. The results help in validating the application of the proposed baseflow-based storage estimates in different aquifers and climatic regions. The proposed approach is simple and computationally efficient for estimating baseflows and groundwater storage changes in poorly-gauged watersheds.