Hargreaves equation (HG), which lacks a wind speed (u2) term, was modified, through a linear regression calibration method, into LHGu which hasu2terms. LHGu is effectively a simplified method for approximating FAO-56 Penman-Monteith equation (FPM) daily reference evapotranspiration (ETo) in tropics with only temperature data. In LHGu, the “0.0023” constant term in HG was calibrated as a shifted power function ofu2, and the calibration constant was parametrized as a quadratic function ofu2. LHGu was developed using simulated constantu2data and historical temperature data for four sites in West Africa: Abidjan, Accra, Daloa, and Lome. LHGu matched FPMETobetter than HG over a wide range ofu2: for Accra, foru2range 0.5–6.0 m/s, the modified coefficient of efficiency,E1, varied narrowly (0.83–0.98) for LHGu but widely (0.14–0.95) for HG optimized foru2=2.0 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 dailyu2. LHGu is useful for quickly computing practically accurate estimates of FPMETofor varying dailyu2where only temperature data are available.