Sensitivity of some potential evapotranspiration estimation methods to climate change

A simulation approach was used to generate estimates of the sensitivity of potential evapotranspiration (ET_p) to climate change using eight alternative ET_p estimation methods. The methods, which differ in structure and data requirements, were: Thornthwaite, Blaney-Criddle, Hargreaves, Samani-Hargreaves, Jensen-Haise, Priestley-Taylor, Penman, and Penman-Monteith. The simulations were performed using climate data from five sites in the North American Great Plains. The results indicate that the methods differ, in some cases significantly, in their sensitivities to temperature and other climate inputs. The degree of agreement among the methods is affected, to some extent, by location and by time of year. When two GCM-derived scenarios of climatic change were applied, the predicted response of ET_p varied in magnitude and in some cases in sign, according to the estimation method used. The differences among methods can be attributed both to differences in their sensitivities to climate, and to differences in the climatic factors they consider. The implications of these findings for studies of climatic change are discussed.