Last updated October 15, 2021
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California Floods January 2017

United States

On January 3 and 4, the first of two back-to-back atmospheric river storms brought heavy rain, mountain snow, and localized flooding to central California. The second storm, fueled by a powerful, long-duration atmospheric river funneling warm and moist air from southeast of Hawaii, hit central and northern California beginning late on January 7 and pushed major rivers past flood stage levels and drove extreme gusts, leading to power outages as well as rock and mudslides. Temperatures during the second storm were warm, which pushed snow levels back above the Sierra passes and converted snowfall to rainfall, elevating flood risk. A 3rd storm dropped additional heavy rain and snowfall amounts up to 4 inches on January 10 and up to 6 inches on January 11. These storms are consistent with observed trends and projections indicating that extreme precipitation in California, as well as globally, increases generally in a warming climate. Moreover, projections indicate that the most intense atmospheric river storms in particular increase in California in a warming climate. In addition, warmer temperatures means more precipitation falls as rain rather than snow, elevating the risk of flooding. Snow levels retreat to higher elevations, diminishing snow pack and increasing runoff and flooding risk.

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Flooded Road