Climate Change to Intensify Atmospheric River Flooding Damages in the Western United States

As rapidly advancing research develops our understanding of atmospheric rivers (ARs) from a meteorological perspective, less work has been done analyzing the tangible impacts of these phenomena. This study quantifies predicted insured flood losses associated with the impacts of anthropogenic climate change on landfalling ARs across the Western United States. Looking at five regions, Arizona, Southern and Northern California, Oregon, and Washington, we predict significant increases in AR-induced flood damages as a result of climate change in every region through to the end of the 21st century. Using 40 years of historic National Flood Insurance Program (NFIP) daily claims and payment information combined with an AR events catalog constructed through a climate reanalysis (Gershunov et al. 2017), we model insured losses as a function of ARs’ mean and maximum integrated water vapor transport (IVT), duration in days, category (Ralph et al. 2019), and number of policies in each respective region. We extrapolate this model to 17 AR event forecasts (Gershunov et al. 2019) under the assumption of Representative Concentration Pathway 8.5 (RCP8.5). Our results are significant not only for property owners at risk, but for the tax-payers who fund the debt of the NFIP. Although our results show that, on average, ARs are expected to become more damaging in the next century due to climate change, the realization of these results is not inevitable. Our quantification of future impacts allows policy makers to assess how much cost society is willing to tolerate before action is taken against climate change.