Predicting Landscape Sensitivity to Present and Future Floods in the Pacific Northwest, USA

TitlePredicting Landscape Sensitivity to Present and Future Floods in the Pacific Northwest, USA
Publication TypeJournal Article
Year of Publication2015
AuthorsSafeeq M, Grant GE, Lewis SL, Staab B
JournalHydrological Processes
Date Published12/2015
KeywordsPacific Northwest; floods; hydrologic extremes; peak flow; rain-on-snow; climate change; principal component analysis

Floods are the most frequent natural disaster, causing more loss of life and property than any other in the United States. Floods also strongly influence the structure and function of watersheds, stream channels, and aquatic ecosystems. The Pacific Northwest is particularly vulnerable to climatically-driven changes in flood frequency and magnitude, because snowpacks that strongly influence flood generation are near the freezing point and thus sensitive to small changes in temperature. To improve predictions of future flooding potential and inform strategies to adapt to these changes, we mapped the sensitivity of landscapes to changes in peak flows due to climate warming across Oregon and Washington. We first developed principal component based models for predicting peak flows across a range of recurrence intervals (2-, 10-, 25-, 50-, and 100-years) based on historical instantaneous peak flow data from 1000 gaged watersheds in Oregon and Washington. Key predictors of peak flows included drainage area and principal component scores for climate, land cover, soil, and topographic metrics. We then used these regression models to predict future peak flows by perturbing the climate variables based on future climate projections (2020s, 2040s, and 2080s) for the A1B emission scenario. For each recurrence interval, peak flow sensitivities were computed as the ratio of future to current peak flow magnitudes. Our analysis suggests that temperature induced changes in snowpack dynamics will result in large (>30-40%) increases in peak flow magnitude in some areas, principally the Cascades, Olympics, and Blue Mountains and parts of the western edge of the Rocky Mountains. Flood generation processes in lower elevation areas are less likely to be affected, but some of these areas may be impacted by floodwaters from upstream. These results can assist land, water, and infrastructure managers in identifying watersheds and resources that are particularly vulnerable to increased peak flows and developing plans to increase their resilience.