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 sys-tems design, water management under irrigated and rainfed production. Underthe sahelian conditions in the Senegal River Valley that receives less than 300 mmannual rainfall, rice crop water use should be estimated for the sustainability of theresource. Study focus: However the Penman–Monteith (PM) equation is revealed the mostaccurate one; it necessitates several climatic parameters that are not always avail-able mostly in the developing countries. The objective of this study was to evaluatethe performance of 16 ETo equations against the ASCE-PM equation under thesahelian conditions at Ndiaye and Fanaye (Senegal) for alternate equation forETo estimation with less climatic parameters. The results showed that the Har-greaves, modified Hargreaves, Ravazzani and Tralkovic equations systematicallyoverestimated 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 relativelybetter at Fanaye with 5.5% and 9.6% PE, fitting slopes of 0.92 and 1.05, and meanratio (MR) of 1.00 and 1.14, respectively. Mass transfer equations of Trabert andMahringer also had good performance compared to the Penman–Monteith equa-tion. New hydrological insights for the region: Overall, Valiantzas, Trabert, Romanenko,Schendel and Mahringer equations were the promising equations that could be usedfor reference evapotranspiration estimation in the Senegal River Valley.