Developing simplified Regional Potential Evapotranspiration (PET) estimation method for Abbay river basin

Abstract

Regional Potential Evapotranspiration (PET) estimation method was developed to estimate the potential evapotranspiration (reference evapotranspiration) over Abbay Basin as a function of basin maximum and minimum temperature, and modulated by site specific elevation data. The method is intended to estimate PET in largely un-gauged locations of Abbay basin. The new model was calibrated based on data from twenty three stations in the basin. Except two stations, which showed model performance (R²) to be less than 50%, performance of the regional model is encouraging. More than 50% of the stations’ performance (R²) is above 70% and the remaining stations performance is between 60 and 70 %. Therefore, the regional model can be used to estimate monthly potential evapotranspiration at any un-gauged location in the Abbay basin provided elevation data is available. The benefit of the new model is that site specific temperature data is not required as the basin average temperature modulated by site specific altitude ensures the local potential evapotranspiration (PET) estimate. The method is simple and can be used as alternative estimation method for agricultural and water resources planning, and studying the hydrology of the Basin. Practitioners in irrigated agriculture and water resources planning can benefit from the developed regional method. The author cautions the use of the method doesn’t substitute the availability of site specific data and should be used only under no or little data condition.

Keywords: Abbay basin, FAO Penman-Monteith method, Regional PET method.