Estimation of Reference Evapotranspiration during the Irrigation Season Using Nine Temperature-Based Methods in a Hot-Summer Mediterranean Climate

The FAO-56 Penman–Monteith (PM) equation is regarded as the most accurate to estimate reference evapotranspiration (ETo). However, it requires a broad range of data that may not be available or reasonable quality. In this study, nine temperature-based methods were assessed for ETo estimation during irrigation at fourteen locations distributed through hot-summer Mediterranean climate region Alentejo, Southern Portugal. Additionally, each location, Hargreaves–Samani radiation adjustment coefficient (kRs) was calibrated and validated evaluate appropriateness using standard value, creating locally adjusted (HS) equation. accuracy method evaluated by statistically comparing their results with those obtained PM. Results show calibration kRs, HS can used daily acceptably well, RMSE lower than 0.88 mm day?1, an error 4% R2 higher 0.69, proving model 8 (out 14) locations. A modified also performed 4 locations, 0.72–0.84 slope varying from 0.95 1.01 0.78. One conclude that, when weather missing, adequate season.