Evaluation of sixteen reference evapotranspiration methods under sahelian conditions in the Senegal River Valley

Study region: Reference evapotranspiration (ETo) plays a key role in irrigation systems design, water management under irrigated and rainfed production. Under the sahelian conditions in the Senegal River Valley that receives less than 300 mm annual rainfall, rice crop water use should be estimated for the sustainability of the resource. Study focus: However the Penman–Monteith (PM) equation is revealed the most accurate one; it necessitates several climatic parameters that are not always available mostly in the developing countries. The objective of this study was to evaluate the performance of 16 ETo equations against the ASCE-PM equation under the sahelian conditions at Ndiaye and Fanaye (Senegal) for alternate equation for ETo estimation with less climatic parameters. The results showed that the Hargreaves, modified Hargreaves, Ravazzani and Tralkovic equations systematically overestimated ETo with the highest percentage error of estimate (PE). In contrast, Makkink–Hansen, Oudin and Turc equations systematically underestimated ETo. Temperature based equations of Romenenko and Schendel performed relatively better at Fanaye with 5.5% and 9.6% PE, fitting slopes of 0.92 and 1.05, and mean ratio (MR) of 1.00 and 1.14, respectively. Mass transfer equations of Trabert and Mahringer also had good performance compared to the Penman–Monteith equation. New hydrological insights for the region: Overall, Valiantzas, Trabert, Romanenko, Schendel and Mahringer equations were the promising equations that could be used for reference evapotranspiration estimation in the Senegal River Valley. Keywords: Reference evapotranspiration methods, Evaluation, Senegal River basin, Sahel