Hydrologic projections for the western United States



Motivated by a common interest in establishing data access for climate change impacts analysis, the U.S. Department of the Interior's Bureau of Reclamation (referred to hereinafter as Reclamation) has collaborated since 2007 with federal and nonfederal entities to provide monthly gridded precipitation and temperature data from 112 contemporary climate projections (Coupled Model Intercomparison Project Phase 3 (CMIP3)) over the contiguous United States. The grid size resolution of this downscaled data archive (publicly available at is 1/8° latitude x 1/8° longitude (approximately 12 x 12 kilometers) and covers the period 1950–2099 [Maurer et al., 2007]. Downscaling is necessary to develop hydroclimate data (e.g., precipitation and temperature) from a coarse- resolution climate model grid to a higher-resolution grid, and the CMIP3 archive was downscaled using the statistical method of bias correction. Although approximately 1000 unique users to date have downloaded the precipitation and temperature information contained within the archive (commonly referred to as the bias corrected spatially downscaled, or BCSD-CMIP3, archive), these temperature and precipitation projections have not been used to consistently generate hydrologic projections over the United States and at fine enough scale to perform hydrologic impacts analysis and support local adaptation assessments. Without available hydrologic projections, planners typically develop and apply their own site-specific and local hydrology models to fill this information gap. However, this makes consistent regional intercomparisons of hydrologic impacts of climate change difficult.