Predicting landscape sensitivity to present and future floods in the Pacific Northwest, USA

Abstract

Floods are the most frequent natural disaster, causing more loss of life and property than any other in the USA. 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 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. 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.

Characterizing Runoff and Water Yield for Headwater Catchments in the Southern Sierra Nevada

“…However, increased warming has led to significant reductions in mountain snowpack accumulation and earlier snowmelt throughout the western U.S. Mote et al, 2005;Harpold et al, 2012). As a result, declines in dry season streamflow (Luce and Holden, 2009;Safeeq et al, 2013), earlier streamflow timing (Stewart et al, 2005;Maurer et al, 2007), and altered flood risk due to a potential increase in peakflow (Hamlet and Lettenmaier, 2007;Tohver et al, 2014;Safeeq et al, 2015a) have been reported across the region. As temperatures continue to warm, much of the region is expected to experience a shift from 1 solid (i.e., snow) to liquid (i.e., rain) phase precipitation (Knowles et al, 2006;Klos et al, 2014;Safeeq et al, 2015b).…”

Influence of winter season climate variability on snow–precipitation ratio in the western United States

“…As temperatures continue to warm, much of this region is expected to experience a shift from solid to liquid phase precipitation (Knowles et al , ). More precipitation falling as rain instead of snow, and consequently a lower total snowfall to precipitation ratio (hereinafter referred to as snow fraction, S f ), would affect total snow accumulation and the timing of snowmelt and runoff regimes, potentially leading to higher winter floods and lower flow in late spring and summer (Safeeq et al , , ). In any given region, however, changes in S f would depend on overall climatic regime as well as the corresponding changes in temperature and precipitation.…”

Linking Hydroclimate to Fish Phenology and Habitat Use with Ichthyographs

“…Climate change is likely to influence both streamflow [19–20] and water temperature [3], thereby increasing the potential for physiological stress in fish populations [21]. Using the ichthyograph, managers can not only identify points in a species’ life cycle where hydrologic conditions may already be reaching physiological limits, but also determine whether future conditions are expected to lie outside the hydrologic conditions experienced in the past, and may represent critically-vulnerable time periods in a species’ life history.…”