Evapotranspiration estimation of crops protected by windbreak in a Mediterranean region

This study is part of a number of studies designed to improve the applicability of the FAO56 model (Irrigation and Drainage Paper by the FAO); the aim of this study is to estimate the crop evapotranspiration (ETc) protected by windbreaks.The study was conducted in three steps: (i) We parameterised the effects of the windbreak on the inputs to the FAO56 model. The calibration parameters were obtained from an experimental study performed on two typical crops of the Mediterranean environment, durum wheat and beans. The former is a rain-fed crop, and the latter is an irrigated crop. A new modified version of the FAO56 model, named the FAO56-wb, which takes into account the windbreak effects, is suggested. (ii) We validated the evapotranspiration (ETwb) provided by the FAO56-wb in daily and seasonal scales. The validation was performed using an independent data set of measured soil-water balances that can determine the evapotranspiration (ET) at various distances from the windbreak. The calculated data of the ETwb and the measured data agree, both in the daily and in the seasonal scales, as demonstrated by the Relative Root Mean Square Error test (RRMSE, between 19.9 and 16.3 for durum wheat and between 12.3 and 16.7 for beans) and by the linear regression (R2 > 0.8 for durum wheat and R2 > 0.9 for beans). (iii) We evaluated the simulation of the ETwb for durum wheat and beans using a 25-year series of agro-meteorological data. The FAO56-wb simulates the evapotranspiration as a function of the porosity of the barrier. The simulations demonstrated the windbreak's potential to contain the evapotranspiration of durum wheat and beans in a semi-arid environment, such as the Mediterranean. The effects on ET reduction were more clearly seen with the use of a windbreak with low porosity (20%) and 3 m in height. In this case, a maximum reduction of 31% of the evapotranspiration in a summer crop, such as beans, occurred within a distance from the windbreak equal to 15 times the barrier height.The results showed that the FAO56-wb is a useful tool to predict the effects of a windbreak even though the model requires only a few agro-environmental inputs.

► The use of windbreak is a dry farming practice which reduces evapotranspiration.
► In case of windbreak, FAO56 model calculates ETc if new parameters are introduced.
► Field surveys let to parameterise the windbreak effects on the inputs to the FAO56.
► Few agro-environmental inputs are required to model the effect of windbreak.
► Modified FAO56 simulates the benefits on water crop in presence of windbreaks.