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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 Nina

La Nina (translated from Spanish as "little girl") is a natural ocean-atmospheric phenomenon marked by cooler-than-average sea surface temperatures in the central Pacific Ocean near the equator. According to the National Oceanic and Atmospheric Administration, a wintertime La Nina climate pattern is in place for Winter 2017/2018, and there is a 50-percent chance it will affect the United States well into Spring 2018. Typically, La Nina climatic patterns include cooler, wetter weather in the northern United States, and warmer, drier weather in the southern states.

In California, La Nina usually brings drier and warmer conditions to Southern California. For Winter 2017/2017, NOAA's temperature and precipitation outlooks suggest climate patterns resembling those of a weaker La Nina. Less-than-normal precipitation over an extended period of time can contribute to water-supply problems and potential drought.


Winter Weather in California Keeps CAWSC Field Crews Busy

Stormy weather: How the USGS goes to work monitoring its effects

Overview of the ARkStorm scenario

Anticipating the Environmental and Environmental-Health Implications of Extreme Storms: ARkStorm Scenario

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.