HEC-HMS Technical Reference Manual Evaporation and Transpiration Current: Available Evaporation and Transpiration Methods PDF Download PDF Download page Available Evaporation and Transpiration Methods. Current page All pages Available Evaporation and Transpiration Methods A total of seven different evapotranspiration methods are available for use within HEC-HMS. These methods include:Hamon MethodHargreaves MethodPriestley Taylor MethodPenman Monteith MethodMonthly Average MethodSpecified EvapotranspirationAnnual EvapotranspirationThe following sections detail their unique concepts and uses. ×