Hydrologic impact of historic atmospheric rivers on the Rillito creek watershed in Tucson, Arizona

Davian Peterson1, Martha Whitaker1
1Department of Hydrology and Atmospheric Sciences, University of Arizona

Atmospheric rivers are both a threat and a source of water to the west region of the United States. Drawing moisture from the Pacific Ocean, these long corridors of water vapor transport large quantities of water across the troposphere and serve as a critical source of precipitation throughout cold seasons in the Southwest, contributing specifically to Arizona’s winter precipitation patterns. However, The Pima County Regional Flood Control District has observed that atmospheric rivers are characteristically responsible for extreme precipitation and often lead to flooding which destroys public and private property and threatens lives. As climate change increases sea surface temperatures, atmospheric rivers will likely intensify, worsening flooding conditions from October to March. The District is evaluating this impact specifically on extreme precipitation in the Rillito Creek watershed in Tucson, Arizona. Precipitation data were analyzed from NOAA’s Tucson International Airport rain gage and streamflow data from US Geological Survey stream gauges over a 1979-2009 observation period. These datasets were then compared to water vapor quantities that exceeded 250 kg m-1 s-1 for more than 12 hours. This information comes from NASA’s atmospheric model called Modern-Era Retrospective Analysis for Research and Application (MERRA). The comparison revealed that atmospheric rivers more frequently resulted in extreme precipitation events (exceeding the 98th percentile). We then discuss the impacts of climate change on flooding through this trend.

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