Collaborative Research: Development of 21st-Century Precipitation Scenarios Using Probabilistic Downscaling Techniques

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Increased annual total precipitation across much of the contiguous U.S. during the latter portion of the 20th century has largely been attributed to a disproportionate change in large magnitude precipitation events and has spurred interest in projecting precipitation trends into the middle and end of the 21st century. Coupled Atmosphere-Ocean General Circulation Models (AOGCMs) are the primary tools available for constructing such projections, but downscaling tools are needed to obtain climate change information at spatial scales relevant for assessing impacts. Downscaling methods have tended to underestimate the variability of geophysical variables and hence are of limited utility when seeking to quantify changes in extreme (or large magnitude) events. This research project focuses on application of innovative statistical downscaling tools to output from multiple coupled AOGCMs to obtain descriptors of the probability distributions of daily precipitation occurrence and wet-day precipitation amount for stations throughout the contiguous USA. The results will allow us to examine the frequency and magnitude of precipitation events in the 21st century relative to those derived from newly-developed century-long precipitation records from the 20th century. The large number of AOGCM simulations used will also allow an unprecedented opportunity to explicitly consider model-based uncertainty and thereby assess confidence in the derived projections.The research conducted under through project closely relates to the activities of the 4th Assessment team of the Intergovernmental Panel on Climate Change (IPCC) by utilizing climate model products generated within that program. It also is highly complementary with the North American Regional Climate Change Assessment Program (NARCCAP), which is focused solely on dynamical downscaling of multiple variables, including precipitation. The comparison of the results of this project with those from NARCCAP will encompass both statistical and dynamical downscaling to present a comprehensive overview of the range of possible climate states and trajectories. The research results will be disseminated through publications, presentations at professional meetings, and a web site dedicated to making the results available to the climate impacts community. The broader impacts of the project also include education and training of the next-generation of climate change scientists.