Skip to main content
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.

Spring/Summer Weather: Rising Temperatures

In California, Winter 2016/2017 was an active season for atmospheric river (AR) storms. These storms generally carry tremendous amounts of water vapor, bringing large amounts of relatively warm, moist air. Sequences of AR storms in January and February 2017 brought above-average precipitation, which contributed to above-average supplies of streamflow and snowpack. Snowpack melts as temperatures rise, feeding California's rivers and streams. A rapid rise in temperatures may cause snowpack to melt too quickly, contributing to excessive runoff in a short period of time; this could cause flooding events throughout the state. Streamflow data collected by the California Streamgage Network provides real-time data on rivers and streams that is crucial to mitigating hazards associated with floods, flash floods, and debris flow. California's emergency preparedness managers, infrastructure engineers, and water-resource managers use USGS data to inform flood-related decision making.


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.