Publications

Effect of Climate Change on Flooding in King County Rivers: Using New Regional Climate Model Simulations to Quantify Changes in Flood Risk

Citation

Lee, S.-Y., G.S. Mauger, and J.S. Won. 2018. Effect of Climate Change on Flooding in King County Rivers: Using New Regional Climate Model Simulations to Quantify Changes in Flood Risk. Report prepared for King County. Climate Impacts Group, University of Washington.


Abstract

Climate projections indicate an increase in flooding in many Pacific Northwest watersheds over the course of the 21st century, in response to an increasing proportion of mountain precipitation falling as rain instead of snow. Global climate models also project an increase in the intensity in the type of heavy rain events that cause most river-scale flood events. A parallel study, funded by the King County Department of Natural Resources and Parks (DNRP) and the Washington State Department of Ecology, has produced a new set of projections of 21st century climate, developed using a regional climate model. A key feature of these projections is that they provide hourly estimates of future weather conditions (temperature, precipitation, humidity, wind, etc.) and account for changes in both the form of precipitation (i.e., rain vs snow) and storm event intensity. Results from that study are described in a separate report (Mauger et al. 2018). In this study, we used the new projections to model changes in future streamflow and evaluate potential changes in peak flows on the Snoqualmie, South Fork (SF) Skykomish, and Green rivers. For the Green River, we also accounted for the effect of reservoir operations by the U.S. Army Corps of Engineers (USACE) at Howard Hanson Dam. Funding for this study was provided by the King County Flood Control District, with additional support from the Critical Infrastructure Resilience Institute.