Hargreaves equation (HG), which lacks a wind speed () term, was modified, through a linear regression calibration method, into LHGu which has terms. LHGu is effectively a simplified method for approximating FAO-56 Penman-Monteith equation (FPM) daily reference evapotranspiration () in tropics with only temperature data. In LHGu, the “0.0023” constant term in HG was calibrated as a shifted power function of , and the calibration constant was parametrized as a quadratic function of . LHGu was developed using simulated constant data and historical temperature data for four sites in West Africa: Abidjan, Accra, Daloa, and Lome. LHGu matched FPM better than HG over a wide range of : for Accra, for range 0.5–6.0 m/s, the modified coefficient of efficiency, , varied narrowly (0.83–0.98) for LHGu but widely (0.14–0.95) for HG optimized for m/s; the corresponding MBE ranges were −0.05–0.01 mm/d for LHGu and 0.02–0.63 mm/d for HG which cannot respond to varying daily . LHGu is useful for quickly computing practically accurate estimates of FPM for varying daily where only temperature data are available.