Identification of Large-Scale Climate Drivers in Flood-Generating Mechanisms

Every year river flooding leads severe social, economic, and environmental consequences. Understanding the flood-generating mechanism is essential for planning and management decisions. It is well-established that Atmospheric Rivers (ARs) are the dominant large-scale atmospheric process that controls the occurrence of heavy precipitation over much of the western US during winter. While recent research has shown that AR events are likely to become more intense as the climate warms, much is still unknown about how local patterns of intense precipitation that accompany ARs might change. This gap in existing knowledge of regional changes limits the ability of communities to formulate actionable responses to the changing risks of floods.

We have developed methods for connecting changes in the large-scale climate to regional risks of heavy precipitation and flooding through a combination of global climate models, regional climate models, and hydrologic models.  Events with 90th percentile of precipitation are identified and connected with large and regional-scale processes (patterns of sea level pressure, geopotential height and water vapor). These patterns are classified using principal component analysis and clustering approaches. The analysis is focused on the Pacific Northwest area because both main flood mechanisms are associated to large-scale climate and also warm rapidly during the 21^st century has been projected in this region with consequences in flood intensity and frequency.  The goal of the study is to use intensive modeling in a few locations to develop methods for assessing the effect of global climate change on flood risks based on statistical analysis of many climate model simulations.