Abstract
Abstract. Atmospheric rivers (ARs) account for more than 75 % of heavy precipitation events and nearly all of the extreme flooding events along the Olympic Mountains and western Cascade Mountains of western Washington state. In a warmer climate, ARs in this region are projected to become more frequent and intense, primarily due to increases in atmospheric water vapor. However, it is unclear how the changes in water vapor transport will affect regional flooding and associated economic impacts. In this work we present an integrated modeling system to quantify the atmospheric–hydrologic–hydraulic and economic impacts of the December 2007 AR event that impacted the Chehalis River basin in western Washington. We use the modeling system to project impacts under a hypothetical scenario in which the same December 2007 event occurs in a warmer climate. This method allows us to incorporate different types of uncertainty, including (a) alternative future radiative forcings, (b) different responses of the climate system to future radiative forcings and (c) different responses of the surface hydrologic system. In the warming scenario, AR integrated vapor transport increases; however, these changes do not translate into generalized increases in precipitation throughout the basin. The changes in precipitation translate into spatially heterogeneous changes in sub-basin runoff and increased streamflow along the entire Chehalis main stem. Economic losses due to stock damages increase moderately, but losses in terms of business interruption are significant. Our integrated modeling tool provides communities in the Chehalis region with a range of possible future physical and economic impacts associated with AR flooding.
Highlights
On 3 December 2007, an atmospheric river (AR) event made landfall on the West Coast of the US
The thermodynamic response of these atmospheric structures will likely lead to significantly more water vapor content and fluxes
Others have hypothesized that a warmer climate will lead to more intense AR-related flooding events and societal impacts
Summary
On 3 December 2007, an atmospheric river (AR) event made landfall on the West Coast of the US. Lewis County, within which the most affected part of the Chehalis River basin lies, experienced the largest impact with USD 166 million in damages and 46 % of its agricultural land flooded (Lewis County, WA, 2009) While this event was extreme, more than 50 % of the total cool-season precipitation and more than 75 % of heavy precipitation (top decile) on the west coast of Oregon and Washington is related to AR events (Rutz et al, 2014). We focus on the Chehalis River basin in western Washington to provide an end-to-end model of severe weather, physical impacts and economic consequences of ARs in a warmer climate. The modeling system is intended to provide decision makers with information about the range of physically plausible changes in flood-causing AR storms and floods, as well as a tool to quantify the related economic impacts
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