FAO-56 Penman-Monteith Daily ET_𝑜 from Linear Regression Calibrated Hargreaves Equation with Wind Terms in Tropics with Limited Data

Table 3

Example comparison of the number of intermediate calculations required to estimate ET_𝑜 for a day using LHG, LHGu, and FPM for latitude = 5.55°N, altitude = 69.0 m, 𝑇_𝑥 = 32.6°C, and 𝑇_𝑛 = 20.1°C; 𝑢₂ = 3.2 m/s.

Estimated; parameter	Units	ET𝑜 equation
		LHG	LHGu	FPM
𝑘HG	—	—	0.0028	—
𝑘4	Mm d^−1	—	−0.5979	—
𝑅𝑎	MJ m^−2 d^−1	22.7655	22.7655	22.7655
Δ	kPa°C^−1	—	—	0.2022
𝛾	kPa°C^−1	—	—	6.7096
𝑒𝑎	kPa	—	—	2.3528
𝑒𝑠	kPa	—	—	3.6356
𝑅𝑠	MJ m^−2 d^−1	—	—	33.8897
𝑅𝑠𝑜	MJ m^−2 d^−1	—	—	25.4641
𝑅nl	MJ m^−2 d^−1	—	—	4.2461
𝑅ns	MJ m^−2 d^−1	—	—	17.5294
𝑅𝑛	MJ m^−2 d^−1	—	—	13.2834
ET𝑜	mm d^−1	5.0	5.4	5.6