California Drought

Drought & Surface Water

Streams, rivers, lakes and reservoirs - collectively referred to as surface water - are important natural resources for irrigation, public supply, wetlands and wildlife. Surface water is also measured as annual runoff, which is the amount of rain and snowmelt drainage left after the demands of nature, evaporation from land, and transpiration from vegetation have been supplied. It supplies most of our basic water needs.

The California Water Science Center measures the flow of surface water, and annual runoff, using a network of more than 500 streamgages that collect real-time data at locations across the state. These gages are part of the larger USGS national streamgage network that contains about 8,000 continuous-record stream-gaging stations. The stream-gaging network provides a continuous source of well-archived, well-documented, and unbiased water data. Streamflow data assist water managers in making daily operational decisions for dealing with water requirements for municipal, industrial, and agricultural purposes, demands for hydroelectric power generation, and for controlling water storage in reservoirs to ensure adequate water supply.

Surface Water, Drought and Climate

The discharge and quality of water from California rivers and reservoirs have broad effects on factors such as water availability, and ecosystem system health. The discharge and quality also fluctuates on timescales ranging from minutes to centuries in complicated ways that seem random at first glance. By taking a large-scale view of these fluctuations and linking them to global scale climatic processes, researchers are beginning to see more structure and predictability than has been previously recognized. For example, the Nation's water resources are tied together on regional scales by their shared responses to temperature and precipitation variations. Understanding these links provides a better scientific basis for predicting and planning for droughts, floods, and water supplies, months to years in advance.

The California Water Science Center has installed webcams at several real-time streamgaging sites across the state. Webcams are another resource used to provide real-time surface-water information to scientists, emergency managers, and the general public.

Select California Streamgages


Several streamgage sites are shown on the map for historical comparison of stream flows affected by the drought. Streamgage sites were selected based upon public and water management interest, and for their long-term historical data record including daily (or more) stream stage readings of at least 50 years.

2018 water year data are provisional and subject to change.

Click or Touch a Streamgage Icon On the Map to Display Drought Related Water Data Graphs for Select Water-Years. Click the home button () to reset map extent and/or reset the Explanation pane.