CHARACTERIZING DROUGHT IN WESTERN U.S. WATERSHEDS: GRID-BASED REGIONAL GEOSPATIAL TOOLS FOR CALIFORNIA AND THE COLORADO RIVER BASIN

The multi-decadal drought that has plagued the western U.S. has prompted the need for tools and information to characterize the drought not only in terms of streamflow but also in terms of landscape conditions and processes that include snow cover, snow melt, soil moisture, evapotranspiration (ET), runoff generation, and recharge. Grid-based regional-scale geospatial tools have been developed to help improve the understanding and evaluation of landscape conditions and processes and to enable short term future projections. The projections can be used by land and water managers to predict, for example, how long it will take to return to more recent long term average conditions following the current multi-year megadrought. Projections can also be used to evaluate trends that may require longer term changes in land and water management. A major advantage of the regional-scale tools is the efficiency in performing intercomparisons of watersheds at multiple scales and providing a more comprehensive and integrated knowledge base for prioritizing resources amidst varying levels of risk. Additionally, short term monthly forecasts that provide information for the entire water year given current antecedent conditions can help resource managers in planning for short term and long-term conditions. We will characterize the evolution of the western drought and why it has been historic, explain the spatial distribution of long term aridification, and give examples of how tools are applied to anticipate hydrologic responses of the landscape to ongoing monthly climate variability. Examples of applications include the use of tools to analyze how much rain or snowmelt is needed to initiate runoff in a watershed or into a reservoir, estimating how changes in the spatial and temporal distribution of precipitation along with changes in air temperature might affect the timing of recharge and the partitioning of available water between recharge and runoff, mapping locations most likely for short term recovery to occur, and identifying locations that refugia for a specified species or ecosystem might be maintained given the projected variability and trends in climate. We will also provide future projections of climate for the next 20-40 years in the region in comparison with historical and recent conditions.