Management of irrigation water in Al-Baha Region, Saudi Arabia using simple and alternative equation to Penman-Monteith equation

Estimation of reference crop evapotranspiration (ETo) is very important in planning and scheduling irrigation water. An estimation of ETo by other simple methods is necessary with the loss of one or more meteorological factors required for estimation by the Penmen-Monteith equation. So, the aim of the 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 and an effective alternative to the Penmen-Monteith equation (PM). Four simple temperature dependent equations, Thornthwaite, Blaney-Criddle, Hamon and Linacre were selected. The results showed that the Linacre method is the best equation for estimating ETo and although the ETo rate was overestimated based on the Linacre equation compared to PM, it had the lowest error percentage (9.55%) in addition to the highest R2 (0.97). After deducing a new and accurate equation based on the Linacre equation and its high ability to estimate the ETo rate and give it values closest to the results obtained using PM in the Al-Baha region in Saudi Arabia, it can be relied upon to estimate the irrigation needs in the Al-Baha region with irrigation systems used in this region.