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The Hydroclimate of the Upper Colorado River Basin and the Western United States

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April 10, 2014
Becky Bolinger
Hosted by Chris Kummerow (advisor), Nolan Doesken, Steve Rutledge, Tom Vonder Haar, Jorge Ramirez (Civil and Environmental Engineering)

Abstract

Understanding water budget variability of the Upper Colorado River Basin (UCRB) is critical, as changes can have major impacts on the region’s vulnerable water resources. Using in situ, reanalysis, and satellite-derived datasets, surface and atmospheric water budgets of the UCRB are analyzed. All datasets capture the seasonal cycle for each water budget component. Most products capture the interannual variability, although there are some discrepancies with atmospheric divergence estimates. Variability and magnitude among storage volume change products also vary widely. With regards to the surface budget, the strongest connections exist between precipitation, evapotranspiration, and soil moisture, while snow water equivalent is best correlated with runoff. Using the most ideal datasets for each component, and bias correcting an underestimation of evapotranspiration, the atmospheric and surface water budgets are brought to balance.

Expanding the ideal datasets selected over the UCRB, an analysis of the errors in atmospheric and surface water budgets is performed for every individual HUC4 basin over the western U.S. Surface water budgets show overall much smaller residual errors than the atmospheric water budgets over the region. Visually analyzing the balances and imbalances, we see that several different areas around the Continental Divide and the Great Basin balance well at the surface, but not as well in the atmosphere; around Arizona, most basins don’t balance at either the surface or atmosphere; many of the Pacific coastal basins and basins in the northern Rocky mountains balance well at the surface and in the atmosphere. These balances/imbalances, climate variability, land cover, and topography are combined to delineate five hydroclimate zones. Seasonal and interannual variability is analyzed for each zone. The Pacific Coast zone shows strong agreement amongst the seasonal cycles of all the water budget components, while most of the other zones show an offset in peaks between components during the winter and summer.