Groundwater storage loss in the central valley analysis using a novel method based on in situ data compared to GRACE-derived data

We estimate long-term groundwater storage loss in California's Central Valley (CV) using a novel data imputation method that combines in situ data with Earth Observations to generate temporally and spatially interpolated groundwater elevations. We combine these data with storage coefficient maps to produce time series of groundwater volume changes which compare well with previously published groundwater storage change estimates for the valley. We also compare our results to groundwater storage changes we calculated using Gravity Recovery and Climate Experiment (GRACE) mission data and show that the two storage estimates are well correlated, but the GRACE volume estimates are lower due the well-known “leakage” effect. While other researchers have accounted for leakage by scaling the GRACE results using various factors and assumptions, our method demonstrates a direct method for calibrating GRACE estimated groundwater change, which can then be applied to future GRACE results in the CV with confidence.