The 'pan coefficient' used when converting Class A pan evaporation to lake evaporation accounts for:
Choose the correct answer
Different rainfall in lake vs pan
Pan overheats relative to large water body — pan evaporation > lake evaporation by factor of ~1/0.7 = 1.43
Wind speed difference only
Color of the pan
Correct Answer
B. Pan overheats relative to large water body — pan evaporation > lake evaporation by factor of ~1/0.7 = 1.43
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Pan coefficient Kp = Lake evaporation / Pan evaporation ≈ 0.7–0.8. Pan coefficient < 1 because: (1) Pan water heats more than lake (less mass, more exposed metal surface); (2) Reflected heat from pan edges increases evaporation; (3) Turbulence differs. IS 5973: Kp = 0.7 for well-maintained land pan. Multiply pan reading by Kp to get lake evaporation.
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