Management of irrigation water in Al-Baha, Saudi Arabia, using a simple alternative to the Penman–Monteith equation

Abstract

Estimating reference crop evapotranspiration (ETo) is very important in the planning and scheduling of irrigation water. A simple method for the estimation of ETo is needed, with fewer meteorological factors that are required for estimation using the Penmen–Monteith equation (PME). The aim of this study was to manage irrigation water in the Al-Baha region of Saudi Arabia using a simple equation to estimate ETo based on air temperature as an effective alternative to the PME. Four simple temperature-dependent equations proposed by Thornthwaite, Blaney-Criddle, Hamon and Linacre were selected for analysis. Of these four equations, the Linacre equation (LE) was found to be best for estimating ETo. Although the ETo rate was overestimated when using the LE compared with the PME, it had the lowest error percentage (9.55%) and the highest R2 (0.97). After deducing a new and accurate equation based on the LE with the ability to estimate the ETo rate, the modified LE produced values closest to the results obtained using the PME for the Al-Baha region. It can thus be relied upon for estimating irrigation needs in the Al-Baha region with the irrigation systems used in the region.