Change in Flood Magnitudes
Pacific Northwest streams are 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. Principal component-based models for predicting peak flows were developed across a range of recurrence intervals (2-, 10-, 25-, 50-, and 100-years) based on historical instantaneous peak flow data from 1000 gauged 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. Regression models were used 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. 21st Century Q (peak flow, cubic meters per second) divided by 20th Century Q. Values higher than 1 indicate increasing flood flows in the future.
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