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Continental-Scale Estimates of Runoff Using Future Climate Storm Events
Cada, P., M. Mehaffey, AND A. Neale. Continental-Scale Estimates of Runoff Using Future Climate Storm Events. 2017 AWRA Summer Specialty Conference, Tysons, VA, June 25 - 28, 2017.
Recent runoff events have had serious repercussions to both natural ecosystems and human infrastructure. Understanding how shifts in storm event intensities are expected to change runoff responses are valuable for local, regional, and landscape planning. To address this challenge, relative changes in runoff using predicted future climate conditions were estimated over different biophysical areas for the CONterminous U.S. (CONUS). Runoff was estimated using the Curve Number (CN) developed by the USDA Soil Conservation Service (USDA, 1986). A seamless gridded dataset representing a CN for existing land use/land cover (LULC) across the CONUS was used along with two different storm event grids created specifically for this effort. The two storm event grids represent a 2- and a 100-year, 24-hour storm event under current climate conditions. The storm event grids were generated using a compilation of county-scale Texas USGS Intensity-Duration-Frequency (IDF) data (provided by William Asquith, USGS, Lubbock, Texas), and NOAA Atlas-2 and NOAA Atlas-14 gridded data sets. Future CN runoff was predicted using extreme storm events grids created using a method based on Kao and Ganguly (2011) where precipitation extremes reflect changes in saturated water vapor pressure of the atmosphere in response to temperature changes. The Clausius-Clapeyron relationship establishes that the total water vapor mass of fully saturated air increases with increasing temperature, leading to the potential for more intense precipitation extremes. Based on the ideal gas law and the Clausius-Clapeyron relationship precipitation extremes can be scaled from one time period to another future time period using temperatures from those same time periods. The above approach was applied to the NASA Earth Exchange (NEX) downscale climate projection gridded data sets (800-meter resolution). Historic average (1950-2005) and future average (average of 2090 to 2099 annual data from IPCC AR5's RCP 8.5 scenario) annual temperature grids were used to create a scalar grid subsequently applied to the existing climate, seamless grids created from NOAA and Texas USGS's data sets as discussed above. The output allows relative comparison between HUC12-, HUC8-, and other regional-scale surface runoff changes in response to climate changes seen in the IPCC future climate scenario (RCP 8.5). The Rocky Mountain and Great Lake region showed the greatest increase in runoff response estimates, with the Gulf Coast and Eastern Seaboard regions showing the lowest increase.
The approach was designed to derive a quantitative approximation of the ecological services provided by vegetative cover, management practices, and other surface features with respect to runoff from current and future extreme weather events across the continental US for incorporation into the EnviroAtlas. Understanding how shifts in storm event intensities are expected to change runoff responses are valuable for local, regional, and landscape planning.
Record Details:Record Type: DOCUMENT (PRESENTATION/SLIDE)
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL EXPOSURE RESEARCH LABORATORY
SYSTEMS EXPOSURE DIVISION
ECOLOGICAL & HUMAN COMMUNITY ANALYSIS BRANCH