Retrospective analysis of water budget for the Mississippi River basin

One of the principal scientific objectives of the GEWEX Continental-Scale International Project (GCIP) is to determine the time/space variability of the hydrological and energy budgets over a continental scale. Mississippi River basin, the third largest river basin in the world, is regarded as an ideal study area for this purpose because of the abundance of historical hydrometeorological data, and the existence of a vast array of hydrometeorological observation networks in the basin. There are many approaches to studying water and energy budgets over Mississippi River basin. One approach is to compute the atmospheric water budget over the area. This approach generally works well for large scale areas. Strategically placed advanced observation instruments are needed to measure relevant hydrometeorological variables. These instruments have been in existence for relatively short time and are very expensive to operate. An alternative approach is to compute water budget on the land surface using retrospective hydrometeorological data. The latter approach was taken in this study. Up to 50 years of monthly precipitation and streamflow discharge data have been collected for more than 200 unregulated catchments in the Mississippi River basin. Also collected are corresponding climatic monthly potential evaporation. Simple assumptions on how evaporation occurs are made to estimate the actual evapotranspiration and soil moisture storage changes. This presentation will show the results of water budgets analysis at different spatial scales: from the catchment scale, to large scale, and ultimately to the continental scale. The results will be compared to atmospheric water budgets, where possible.