Simplified limited data Penman’s ET0 formulas adapted for humid locations

•New evapotranspiration formula not requiring wind data for humid climate.•New formula requiring solar radiation and temperature only for humid locations.•The suggested new formulas were tested using data from humid stations. New reference evapotranspiration formulas based on simplifications of Penman’s equation were developed applicable to humid areas, where wind speed and/or relative humidity data are missing. The new formulas were obtained by empirical calibration adjustments using meteorological data obtained from the humid locations of the CLIMWAT global data base. The performance of the new derived formulas was tested under various climatic conditions using data set monthly and daily data obtained from 16 weather stations at humid locations of California, Florida, and Greece. Comparisons indicated that the suggested formulas performed better than other empirical methods not requiring wind and/or humidity data for the majority of humid locations.