Water Resources Research Act Program

Details for Project ID 2015WA402B

Development and Update of Rainfall and Runoff Intensity-Duration-Frequency Curves for Washington State Counties in Response to Observed and Anticipated Extreme Rainfall and Snow Events

Institute: Washington
Year Established: 2015 Start Date: 2015-03-01 End Date: 2016-02-28
Total Federal Funds: $27,500 Total Non-Federal Funds: $55,046

Principal Investigators: yonas Demissie, Jennifer Adam, Akram Hossain

Abstract: Storm water and flood management infrastructures are commonly designed to handle specific design storms derived from historical rainfall intensity-duration-frequency (IDF) curves based on the assumptions that these rainfall characteristics will remain unchanged throughout the design lifetimes of the infrastructures. However, the historical and projected increase in frequency and intensity of extreme rainfall may violate this assumption, making the infrastructures inadequate and vulnerable for flooding as seen more frequently in recent years. In Washington State, much of the drainage installed in the last several decades uses IDF curves that might be outdated, and thus they may not be effective to handle today and future storms. To address the non-stationarity of the storm events and minimize the associated flood risk, the proposed study will update the current IDF curves in Washington State using recently observed and projected precipitation data. The study will develop new county-level rainfall and runoff IDF curves, taking into consideration the spatial and temporal variations of precipitation in drainage areas, effects of snow-pack and snow-melt, and impacts of future climate change and uncertainty. Regional frequency analysis will be used to improve the accuracy and spatial representation of the IDF curves. Bayesian statistics will be used to quantify the uncertainty associated with extreme probability distributions used to describe the extreme rainfall. Watershed and snow models will be used to develop runoff IDF curves that explicitly account for effects of snow and drainage characteristic into the IDF curves and related designs. High resolution (12 km spatial and 1 hour temporal) climate projections will be used under various scenarios to predict the future extreme rainfall patterns and update the IDF curves. The resulted IDF curves are expected to provide more reliable, up-to-date, and spatially resolved characteristics of storm events and associated flood risk for each county in Washington State.