Combined Effect of Global Climate Projection and Hydrologic Model Uncertainties on the Future Changes of Streamflow

The projected changes to streamflow for a river basin in the Pacific Northwest U.S. are investigated using statistically downscaled output from 8 global climate model projections. The downscaled meteorological data is used to drive three hydrology models with different complexities: the Sacramento Soil Moisture Accounting (SAC-SMA) model, Conceptual Hydrologic MODel (HyMOD) and Thornthwaite-Mather model. This is meant to consider the uncertainty in hydrologic model selection. The uncertainty in model parameterization is addressed by calibrating the models with three different objective functions. The total uncertainty is investigated for dry (summer) and wet (winter) season for two emission scenarios namely A1B and B1 in each GCM. The results show that the hydrologic uncertainty is considerably smaller than climate uncertainty where the total uncertainty for dry season is higher than the one in the wet season. The runoff change for future periods relative to the reference period is also examined showing the decrease in runoff by moving further to future time slices especially in dry seasons.