ATMOSPHERIC RIVERS AND MASS MOVEMENTS IN CALIFORNIA

Atmospheric rivers (ARs) are long, narrow corridors of high water vapor transport that typically occur in the cool season in association with extratropical cyclones. ARs are key atmospheric features in driving cool season (October-May) flooding along the US West Coast. Our recent work indicates that ARs are associated with roughly 75–90% of precipitation events that exceed published intensity-duration thresholds for shallow landslides in California, with moderate intensity, multi-hour durations having a stronger relationship with ARs. While ARs are not the only driving factor in generating high intensity precipitation in the cool season, recent research by the authors and others shows they play a significant role in generating mass movements in California and West Coast locations. A trio of different AR–mass movement (or similar) analyses revealed that (1) 13 of 19 (68%) cool-season post-fire debris flow storm events in southern California were associated with ARs; (2) 28 of 34 (82%) of cool-season days with debris flow reports from the National Weather Service offices in northern California were associated with ARs; and (3) 163 of 214 (76%) days with San Francisco Bay Area landslides identified by the USGS between 1871 and 2012 were likely associated with ARs. AR research has made great strides over the last two decades, offering new insights and information that can be utilized by the geomorphology and natural hazards communities. In addition to describing results from the aforementioned studies, this presentation will discuss current topics of AR research as well as challenges, and make suggestions for how AR findings can be applied to studies and operations in geomorphology and natural hazards. We will also discuss existing and emerging tools and datasets from the Center for Western Weather and Water Extremes that can be used by these communities to monitor and study ARs.