The 'evaporation from open water surface' is measured using:
Choose the correct answer
Rain gauge measurement
Class A pan evaporimeter (IS 5973) — open pan with daily water level measurement; multiply by pan coefficient for lake evaporation
Soil moisture sensors only
Stream gauging station
Correct Answer
B. Class A pan evaporimeter (IS 5973) — open pan with daily water level measurement; multiply by pan coefficient for lake evaporation
Why is this the answer?
Evaporation measurement: (1) Class A pan evaporimeter (IS 5973): standard 1.21 m dia × 0.25 m deep floating or land pan; (2) Colorado sunken pan; (3) ISI pan (India). Pan evaporation × pan coefficient (Kp ≈ 0.7–0.8) = lake evaporation. Pan coefficient accounts for pan overheating. India: annual pan evaporation = 150–200 cm in arid areas.
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