Impacts of climate change on Missouri River Basin water yield

Water from the Missouri River Basin is used for multiple purposes. The clim atic change of doubling the atmospheric carbon dioxide may produce dramatic water yield changes across the basin. Estimated changes in basin water yie ld from doubled CO2 climate were simulated using a Regional Climate Model ( RegCM) and a physically based rainfall-runoff model. RegCM output from a fi ve-year, equilibrium climate simulation at twice present CO2 levels was com pared to a similar present-day climate run to extract monthly changes in me teorologic variables needed by the hydrologic model. These changes, simulat ed on a 50-km grid, were matched at a commensurate scale to the 310 subbasi ns in the rainfall-runoff model climate change impact analysis. The Soil an d Water Assessment Tool (SWAT) rainfall-runoff model was used in this study . The climate changes were applied to the 1965 to 1989 historic period. Ove rall water yield at the mouth of the Basin decreased by 10 to 20 percent du ring spring and summer months, but increased during fall and winter. Yields generally decreased in the southern portions of the basin but increased in the northern reaches. Northern subbasin yields increased up to 80 percent: equivalent to 1.3 cin of runoff on an annual basis.