GRACE Estimates of Terrestrial Water Storage: Validation and Applications

Through the application of a filtering technique designed to identify and remove correlations between certain GRACE Stokes coefficients, we have obtained a significant variance reduction in the monthly GRACE spherical harmonic solutions, such that the seasonal cycle of terrestrial water storage can be observed at spatial scales as short as 300 km. Recently, we performed a cross-validation by comparing GRACE water storage estimates to in situ measurements of soil moisture and groundwater storage for a region approximately 280,000 km2 in size centered in Illinois. Estimates of the seasonal cycle of total water storage from these two observations show good agreement, having an rms difference of 20 mm. Furthermore, model results indicate that much of this difference can be explained by discrepencies in spatial sampling. The availability of such high resolution water storage estimates expands the types of problems to which GRACE data can be applied, and we will discuss some of these applications.