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USGS - science for a changing world

California Flood Science

Monitoring Potential Flood Hazards

To help emergency managers and others prepare for floods, the USGS delivers a continuous source of streamflow information that provides the scientific basis for decision-making related to protection of life and property from water hazards. The USGS California Water Science Center maintains a network of nearly 500 streamgages that monitor hydrologic conditions throughout the State. Core data collected at streamgages are surface water levels that are used to determine the amount of water flowing in a river or stream. The USGS uses streamgage data to provide flood-warning alerts when surface water levels change rapidly, or reach flood-stage levels, which can signify potential hazardous conditions for downstream locations.

Winter Weather: La Niña?

The USGS California Water Science Center plays an active role in preparing the State for potential water-related hazards during winter weather. There is a 70 percent chance of a weak La Nina forming during the Northern Hemisphere during fall 2016 and a 55 percent chance of La Niña conditions persisting during winter 2016-17, according to the Climate Prediction Center. Although past La Niña events have historically favored near normal or dry winter months, past conditions do not guarantee future outcomes. The USGS Streamgage Program provides information to help resource managers, emergency preparedness personnel, and the public to make informed decisions during winter weather events, and plan for water-related hazards associated with normal to wet precipitation in California.

Streamgage Information

The U.S. Geological Survey has been measuring streamflow in the U.S. for over 120 years. We operate more than 7,500 streamgages in the U.S. and almost 400 in California.

Flood Activity

Current California flood alerts, including event summaries and streamgaging activity.

Debris Flow

Post-fire debris flows are a destructive landslide hazard. The USGS has conducted hazard assessments for select California wildfire burn areas.


A collection of USGS flood related photos, videos, news and publications.