Analysis and calibration of empirical relationships for estimating evapotranspiration in Qatar : case study

Knowledge of evapotranspiration (ETₒ), which is the process of water loss from vegetated soils due to evaporation and transpiration, is important in real-time irrigation management and water-resource allocation, particularly in water-scarce regions. In this study, several methods used in estimating evapotranspiration, including the Blaney-Criddle, Hargreaves-Samani, Jensen-Haise, Linacre, and Turc methods were calibrated and validated against the Penman-Monteith model, which is considered as the standard method of estimating evapotranspiration. The paper utilizes data from the Doha International Airport meteorological station over a period of 30 years (January 1985–December 2014). ETₒ values were estimated using the different methods. These values were then compared to those obtained by the Penman-Monteith method. Using appropriate indicators, the Turc method was found to be the best for estimating ETₒ over Doha (R2=0.9519R2=0.9519, RMSE=1.4511  mm day−1RMSE=1.4511  mm day−1, and MAE=1.1633  mm day−1MAE=1.1633  mm day−1). The Turc method comes in handy for estimating ETₒ over Qatar as it utilizes only three meteorological parameters (mean temperature, relative humidity, and solar radiation), which are easily measurable over that area.