California Drought


Runoff Estimates for California

The runoff estimate for California is the quantity of water that is discharged - or "runs off" - from the state, in monthly or annual time periods. Runoff occurs as the result of precipitation (both rainfall and snowfall) that is in excess of the demands of evaporation from land surfaces, transpiration from vegetation, and infiltration into soils. The water that remains available, or runoff, is the amount of water that makes its way to streams, rivers, and, possibly, to the ocean. The USGS stream gaging network provides accurate stream flow records and enables the compilation of runoff data for California. It is important to note that because the number of streamgages in operation can vary from year to year, more accurate estimates of annual runoff are made during years when a larger number of gages are operational. Periods of sparse streamgage data, such as the years prior to 1930, may have unreliable runoff estimates. Runoff data are from USGS Water Watch.

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Monthly runoff data for California is provided by the USGS Water Watch website. The "Past Flow/Runoff" tool for the State of California provides the annual summary and rank of runoff by water-year. The "Drought" tool provides the State duration hydrograph of monthly runoff values by water-year for California. A statistical lowess curve is generated for the annual monthly runoff using an R software script.




The Lowess Smoothing Runoff line presents the best fit curve through the annual runoff data to help see the relation between variables and foresee trends.

Click and drag across the graph to zoom.
Roll over graph lines for specific values.
Click legend to toggle graph lines on and off.



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The average Olympic pool contains 660,000 US Gallons

Water year data are from October 1 to September 30.