Question

What is the correct expression of parameter Ea in Penman’s equation?

(a) Ea = 0.35 (1 + V2/160) (es – ea)

(b) Ea = 0.35 (1 + V2/160) (es + ea)

(c) Ea = 0.35 (1 – V2/160) (es – ea)

(d) Ea = 0.35 (1 – V2/160) (es + ea)

I got this question in a national level competition.

This is a very interesting question from Water Requirements of Crops topic in division Water Requirements of Crops of Irrigation Engineering

Answer 1

Correct answer is (a) Ea = 0.35 (1 + V2/160) (es – ea)

Easy explanation: The parameter Ea is estimated by as: Ea = 0.35 (1 + V2/160) (es – ea).

Where, V2 is the wind mean speed at 2m above the ground in km/day, es  is Saturation vapour pressure at mean air temperature in mm of Hg, and ea is actual mean vapour pressure of air in mm of Hg.