The Effects of Climate Change on the Water Resources and Hydropower Production Capacity of the Upper Colorado River

The Upper Colorado River Basin (UCRB), comprised of the Colorado and Gunnison
River basins, is regulated by 17 major reservoirs to provide water supply, flood control, and
hydropower. It is the prime water source for much of the western United States, as well as key
wildlife and fish habitat. Climate change is an issue of concern on the basin due to the sensitivity
of snow accumulation processes that dominate runoff generation within the region. Climate
models project an average warming of up to 4o F, coupled with a decline in precipitation falling
as snow. There is no numerical consensus of the magnitude of change in precipitation, but there
is general agreement that precipitation changes will be exacerbated by increased
evapotranspiration rates, reducing overall runoff. This is expected to cause a decline in runoff
and hydropower generation capacity.
Potential impacts of climate change on the hydrology and water resources of the UCRB were
assessed through a comparison of simulated stream flow, temperatures, and reservoir volumes
and storage levels. Future climate conditions derived from climate centers: Meteorological
Research Institute (MRI-CGCM2.3.2), Canadian Centre for Climate Modeling and Analysis
(CGCM3.2 T47), and the Center for Climate System Research at the University of Tokyo with
the National Institute for Environmental Studies and Frontier Research Center for Global Change
(MIROC 3.2) under A2 and B1 emission scenarios were compared to historical conditions.
From the joint venture of the United States Bureau of Reclamation (USBR) and other research
and university facilities, bias-corrected constructed dialogues (BCCA) daily downscaled
precipitation and climate data was processed and used to drive the Watershed Analysis Risk
Management Framework (WARMF) hydrologic model to simulate future changes in the UCRB.
WARMF performs daily simulations of snow and soil hydrology to calculate surface runoff and
groundwater accretion to river segments, lakes, and reservoirs. All model scenarios project a
reduction in 21st century flows, though the magnitude varies with location and elevation. Results
illustrate basin-wide temperature increases at low elevations, with extreme seasonality increasing
at high elevation stations in future climate. Reservoir levels in Blue Mesa declined more than
70%, but other reservoirs showed varying results dependent on location and climactic conditions.
The resultant climate change scenarios will motivate adaptive watershed planning and
management decisions and policies in response a changing climate and mitigate future concerns.