Uncertainty assessment of climate change impacts for hydrologically distinct river basins

The hydrologic uncertainty of climate change impacts in two river basins in the Pacific Northwest of US is investigated. One basin is dominated by snowfall in winter, resulting in snowmelt in spring and early summer, and the other basin is dominated by rainfall in all seasons. In addition to hydrologic uncertainties, we consider the combined effect of two emission scenarios and eight general circulation models (GCMs) in our analyses. Latin Hypercube Sampling (LHS) is employed to sample the Precipitation Runoff Modeling System (PRMS) parameter space and the behavioral parameter sets were obtained according to a statistical performance measure. The results suggest that the relative impacts of uncertainties from different sources vary between the two basins. It is shown that changes in winter runoff are more affected by hydrologic model parameter uncertainty in the snow-dominated basin, while they are less influenced in the rain-dominated basin. The differences in the amount and timing of snowmelt as a result of model parameter uncertainty contribute to the variations of change in winter runoff in the snowfall-dominated basin. This result indicates that climate change impact studies for snow-dominated regions require more cautious interpretation of runoff projections due to considerable uncertainty in estimated hydrologic model parameters.