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A 22-year climatology of cool season hourly precipitation thresholds conducive to shallow landslides in California

TitleA 22-year climatology of cool season hourly precipitation thresholds conducive to shallow landslides in California
Publication TypeJournal Article
Year of Publication2018
AuthorsOakley N.S, Lancaster J.T, Hatchett B.J, Stock J., Ralph FM, Roj S., Lukashov S.
JournalEarth Interactions
Date Published2018/07
Type of ArticleArticle
ISBN Number1087-3562
Accession NumberWOS:000438703000001
KeywordsAtmosphere-land interaction; atmospheric rivers; Communications/decision making; cool season; debris flows; duration control; effects; Emergency preparedness; extreme precipitation; Geology; Hydrometeorology; initiation; intensity; orographic; rainfall; sierra-nevada; southern california; Storm; western united-states

California's winter storms produce intense rainfall capable of triggering shallow landslides, threatening lives and infrastructure. This study explores where hourly rainfall in the state meets or exceeds published values thought to trigger landslides after crossing a seasonal antecedent precipitation threshold. We answer the following questions: 1) Where in California are overthreshold events most common? 2) How are events distributed within the cool season (October-May) and interannually? 3) Are these events related to atmospheric rivers? To do this, we compile and quality control hourly precipitation data over a 22-yr period for 147 Remote Automated Weather Stations (RAWS). Stations in the Transverse and Coast Ranges and portions of the northwestern Sierra Nevada have the greatest number of rainfall events exceeding thresholds. Atmospheric rivers coincide with 60%-90% of these events. Overthreshold events tend to occur in the climatological wettest month of the year, and they commonly occur multiple times within a storm. These state-wide maps depict where to expect intense rainfalls that have historically triggered shallow landslides. They predict that some areas of California are less susceptible to storm-driven landslides solely because high-intensity rainfall is unlikely.

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