Databases > Evapotranspiration Data

California Evapotranspiration Data

This website offers evapotranspiration data for two purposes: water balances, and irrigation scheduling and design. **For an explanation of the data and calculation methods, please click here.**


Note: The California Department of Water Resources ETo Zone Map separates California into 18 zones.  For this project only 13 zones were looked at in determining ETc.  The other zones had very little irrigated agriculture, which was grouped into the closest ETo zone.



Step 1.  Select data type*


Step 2.  Select irrigation method


Step 3.  Select relative precipitation year

ETo Zone Map

Step 4.  Select ETo Zone

Click on the image to the right for an ETo zone map (NOTE: Zone 4 data is used for both Zones 3 and 4, because it is representative of both).



*Monthly ETc used for Water Balances values have been adjusted for decreases in vigor and bare spots.  The estimates by ITRC have concluded a reduction in ETc of approximately 7% (CALFED/ARI Evaporation Study Report). Monthly ETc used for Irrigation Scheduling and Design values have not been adjusted for bare spots and decreased vigor.  These values are best estimates of evapotranspiration throughout California.


If you would prefer to manually browse the data, we offer a text-based listing of zones and data for Water Balance values or for Irrigation Scheduling and Design values.


Additional Helpful Links:

CIMIS data

Transpiration from precipitation

Evaporation from precipitation

ET from precipitation