Assessing the hydrologic impacts of climate change on the Colorado river basin

A grid-based modeling approach consisting of a series of linked, conceptual-type models is developed to assess the hydrologic effects of climate change on large-scale watersheds. The National Weather Service snow accumulation and ablation model is used in conjunction with a 2-layer Variable Infiltration Capacity model (VIC-2L) to simulate historical naturalized streamflow at various nodes within the Colorado River Basin. The model is then run with adjusted meteorological forcings to determine the sensitivity of streamflow and evaporation to potential climate change scenarios. The output of two general circulation models (CGMs) is also used as input to the hydrologic simulation models to test a more realistic spatial pattern of precipitation and temperature changes. Results indicate a reduction in mean annual flow volume of between 10% and 30% for temperature increases of 1.5C to 5.0C at most locations, with up to 50% flow reduction for the most extreme scenario. A shift in the average hydrograph peak from June to May also occurs for the increased temperature scenarios due to a smaller snow pack and earlier melt. The GCM results are somewhat contradictory, pointing out the uncertainty in climate change related research.