Response of the water balance to climate change in the United States over the 20th and 21st centuries: Results from the VEMAP Phase 2 model intercomparisons

[1] Using the VEMAP Phase 2 data set, we tested the hypothesis that changes in climate would result in changes in the water balance as projected by four terrestrial ecosystem models: BIOME-BGC, Century, LPJ, and MC1. We examined trends in runoff and actual evapotranspiration (AET), changes in runoff in relation to changes in precipitation, and differences in runoff ratios as produced by these models for 13 United States watersheds. Observed climate data were used as inputs for simulations covering 1895– 1993. From 1994 to 2100, the Canadian Centre for Climate Modeling and Analysis (CGCM1) and the Hadley Centre for Climate Prediction and Research (HADCM2) general circulation models provided climate forcing. Runoff and AET trends were significantly positive in the majority of 13 watersheds examined. Percentage changes in runoff exceeded the underlying changes in precipitation and this amplification increased over time. Calculated runoff ratios showed model variability and differences based on the two GCM scenarios.