Sensitivity of Penman–Monteith estimates of reference evapotranspiration to errors in input climatic data

Abstract

The Penman-Monteith (P-M) equation with its new definition of reference crop evapotranspiration (ET0) is recommended by FAO as the standard method of crop water requirement calculation, and also to compare other methods. The ET0 component of the CROPWAT model, which is based on the P-M equation, was examined for sensitivity to errors in input data under the environment of a semi-humid sub-tropic region of Bangladesh. The results showed that the ET0 estimates are most sensitive to maximum temperature and least sensitive to minimum temperature. The order of sensitivity noticed is: maximum temperature > relative humidity > sunshine duration > wind speed > minimum temperature. The sensitivity coefficients showed seasonal variation. The model parameter‘Angstrom’s coefficients’ showed sensitivity to errors in single or pair values. The implications of sensitivity to ET0 estimates and in selecting appropriate method for ET0 estimation in a data-short environment are discussed.