Assessment of Water Storage Trends and Distributions in the Mississippi River Basin as Simulated by IPCC Models and Compared to GRACE Satellite Data

Published work has shown that GRACE water storage estimates are consistent with water storage observations for many river basins. GRACE data can therefore serve as a proxy for water storage data. In this analysis, we compare estimates of total water storage (TWS) anomalies from the GRACE mission to soil moisture (SM) data from IPCC AR4 simulations for the Mississippi River Basin (MSRB). IPCC models do not carry a TWS variable for direct comparison. Therefore, we use the IPCC models\u27 soil moisture content parameter to compare to the GRACE data, because TWS variability in the mid−latitudes is mostly due to SM variability. GRACE data are thus used to validate hydrological output from IPCC models, and trends are then examined to project future water storage for this river basin for the 21st century. Our analysis shows that the composited seasonally−varying TWS anomaly fields for the MSRB computed by IPCC models correlate well with the composite GRACE anomaly field over the period 2002–09, with most correlations greater than 0.9. However, the IPCC model−simulated spatial variations of water storage vary considerably among the models. These differences are in contrast to the broadly similar precipitation and evaporation distributions among the models examined. Our validation efforts suggest that the land models from the IPCC AR4 models need to better capture regional variations in SM before they can be used for reliable projections of this variable