As part of its water use activity, the San Joaquin District has been measuring evaporation from U.S.W.B Class ‘A’ pans located in standard irrigated pasture environments since the 1950s. This site contains a summary of monthly evaporation from pans near Bakersfield from 1958-2007 and at California State University at Fresno from 1968-2007 with the data arranged in tables of monthly averages, standard deviation and standard error, data collection descriptions and a photo of an evaporation pan. Evaporation pan data for specific months is available in the annual tables.

Typical standardized site (irrigated pasture) with a U.S. Weather Bureau Class ‘A’ Pan, tank and DWR agroclimatic station.

AVERAGE MONTHLY EVAPORATION FROM CLASS 'A' PAN IN IRRIGATED PASTURE ENVIRONMENTS NEAR BAKERSFIELD, CALIFORNIA FROM 1958-2007

AVERAGE MONTHLY EVAPORATION FROM CLASS 'A' PAN IN IRRIGATED PASTURE ENVIRONMENTS AT CALIFORNIA STATE UNIVERSTIY AT FRESNO FROM 1968-2007

Evaporation measurements are taken from evaporation pans located at standardized sites (irrigated pastures) with static water levels maintained in the pans by float valves and water supply tanks. The surrounding environment around evaporations pans is critical for obtaining quality evaporation measurements. At locations where environments do not meet standardized criteria, severe weather events may require adjustments to pan measurements (based on correction tables) before estimating crop evapotranspiration. The sites are visited at least weekly to measure evaporation form a U.S. Weather Bureau Class ‘A’ Pan. Other agro meteorological equipment (i.e. rain gauge, anemometer, ambient air thermometers) is installed and read at DWR agroclimatic stations, and this data is collected weekly along with pan evaporation.

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