Storm Tracks over the Southwest United States in CMIP5 Climate Projections and Water Policy Implications

Climate change and population growth are important factors that will affect 21st century southwest United States (SWUS) water supply and demand. This region is important because the Colorado River Basin supplies water to approximately 50 million people, 5.5 million acres of land, and provides 4,200 megawatts of electrical generating capacity. Historical and projected tropical Pacific and Indian Ocean sea-surface temperature (SST) changes and decadal variability related to the Interdecadal Pacific Oscillation (IPO) and their influences on future SWUS climate are investigated. Assessments of storm track patterns and related climate variables in relation to SWUS are made using reanalysis (e.g., NCEP-NCER, ERA-Interim, and NASA MERRA), observations (e.g., GPCP, CMAP, and AMSR-E), and climate model (e.g., NASA GISS, NCAR CCSM4, CanESM2, and NorEMS1-M) data. Model projections based on Representative Concentration Pathway 8.5 in two periods (2010-2039 and 2070-2099) are compared against a 1980-2005 reference period. The region is expected to continue to warm in response to increasing greenhouse gases, which by itself would place additional stress on the Basin's water systems. Fundamentally, this work seeks to address hydrologic effects: whether Basin streamflow might also decrease as a result of storm track shifts away from the region, which would deprive the Basin of requisite winter snowpack. Based on these scientific results, current and potential water resource management policies are discussed. Early results of a limited evaluation of adaptation activities and plans within the region are also made.