Correct option is A
The average value of the pan coefficient for a Class-A evaporation pan is approximately 0.70. This is a standard value used in hydrological studies to estimate evaporation from open water bodies.
Important Key Points:
1. Class-A Evaporation Pan:
· A circular evaporation pan with a standard diameter of 1.21 meters and a depth of 0.255 meters.
· It is widely used in meteorology and irrigation studies to measure the evaporation rate.
2. Pan Coefficient (Kp):
· The pan coefficient accounts for the discrepancy between pan evaporation and actual evaporation.
· The actual evaporation from a water body is calculated as: Eactual=Kp×Epan measured pan evaporation.
3. Standard Value:
· For a Class-A evaporation pan, the average pan coefficient is approximately 0.70, though it may vary depending on environmental factors such as humidity, wind speed, and temperature.
Lake evaporation = Pan Coefficient (Cp) × Pan Evaporation
| Sl. No. |
Types of pan |
Pan Coef. |
Range |
| 1 |
USWB Class A Evaporation Pan |
0.70 |
0.60 - 0.80 |
| 2 |
ISI Pan (Modified Class A) |
0.80 |
0.65 - 1.10 |
| 3 |
Colorado Sunken Pan |
0.78 |
0.75 - 0.86 |
| 4 |
USGS Floating Pan |
0.80 |
0.70 - 0.82 |
