Effects of Climate Change on Natural and Regulated Flood Risks in the Skagit River Basin and Prospects for Adaptation

Currently in progress with leveraged funds
Additional Funds Needed for Completion: $150,000

Background and motivation: Based on GCM scenarios from the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) and subsequent hydrologic modeling studies for the Pacific Northwest, the impacts of climate change on flooding in Western Washington are likely to be substantial. Many rivers draining to Puget Sound show increases in the simulated natural 100-year flood (Q100) of 20–30% by the mid-21st century. To assess the combined effects of increasing natural flood risks and dam operations that determine impacts to regulated flow, we have built a new integrated daily time step reservoir operations model for the Skagit River Basin. The model simulates current operating policies for historical flow conditions and for projected flow for the 2040s and 2080s associated with GCM scenarios. By simulating alternative reservoir operating policies that provide increased flood storage and start flood evacuation one month earlier, prospects for adaptation are considered.

Objective: The overall objective is to estimate changes in regulated flood risk in the lower Skagit River basin under climate change scenarios, and to evaluate the prospects for alternate reservoir management schemes to reduce vulnerability to changing risks.

Project Team: The project team consists of Se-Yeun Lee and Alan F. Hamlet at the University of Washington.

Expected outcome (2010): Preliminary results for the Echam5 A1B scenario for the 2040s and 2080s show increases in natural 100-year floods of 23 % by the 2040s and 27 % by the 2080s relative to historical natural (or unregulated) flows. Current and increased flood storage at Ross Dam and Upper Baker dam is about 40 % and 70 % of historical natural flows respectively. However, because current and increased flood storage mitigate the impacts of natural floods only for the headwaters (which supply a relatively small portion of the total flow at the downstream checkpoints) both current and alternative management for flood control are relatively ineffective at mitigating these increased flood risks in the lower basin. Additional scenarios will help to better define the range of future impacts.

Photo source: http://www.skagitriverhistory.com/Photo_Gallery.htm