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T = 20oC
Qn = 580 cal/cm2/d
v2 = 180 km/d
RH = 75%
The saturation vapor pressure at the overlying air temperature of
20oC is:
eo = 23.37 mb
For the given climatic conditions,
the mass-transfer evaporation rate according to Dunne is:
Ea = (0.013 + 0.00016 × 180) × 23.37 × [(100 - 75)/100] = 0.244 cm/d
The water density and heat of vaporization is:
ρ = 0.998 gr/cm3, and
λ = 586.0 cal/gr.
The evaporation rate due to net radiation is:
En = (580 cal/cm2/d) / (0.998 gr/cm3 × 586.0 cal/gr) = 0.992 cm/d
Penman's ratio (Table 2-4):
α = 2.19
The evaporation rate by the Penman formula is:
E = (2.19 × 0.992 + 0.244) / (2.19 + 1) = 0.757 cm/d. ANSWER.
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