Mapping Reference Evapotranspiration for Iraq Using FAO-Penman-Monteith Method

Abstract

The reference evapotranspiration is imperative for calculating crop and vegetation evapotranspiration, and for describing the local climate. The precise computation of evapotranspiration is vital in applications to irrigation planning, crop water management, basins water balance, climate characterization and climate change studies. For accurate estimation of evapotranspiration,various climatological factors are required which are often not available or incomplete or have doubtful quality. In this article, data from 23 weather stations for 31 years were used to estimate the monthly reference evapotranspiration using FAO Penman–Monteith procedure. Based on the average monthly ETo values, the map of Iraq was divided into three main zones: northern, intermediate, and southern zone in the order of minimum, medium, and maximum values of ETo, respectively. The estimated values of reference evapotranspiration were then generalized on the whole area of Iraq using interpolation and then a contour map of evapotranspiration was provided. This map is necessary in providing approximate values for evapotranspiration in some regions where there are no climatological stations. The interpolation was conducted via two ways. The first way was done by interpolating the factors that included in FAO Penman–Monteith procedure and then calculating the ETo from the resulted data. The second way was conducted by interpolating the ETo values of the recommended 23 available stations. It was found that the resulted values of ETo from the second way is slightly higher than those of the first way. Consequently, the second way is more reliable for design purposes. It was concluded that the maximum ETo occurred on July while minimum occurred on January. The results showed that the most affecting climatological factor on ETo in Iraq based on FAO-Penman-Monteith procedure is the air temperature.