How To Calculate Pan Evaporation In Meter

Pan evaporation is a crucial measurement in hydrology and meteorology, used to estimate water loss from open water bodies and wetlands. Understanding and calculating pan evaporation is vital for water resource management, irrigation planning, and climate studies.

1. Enter the temperature, wind speed, and relative humidity values.
2. Click the ‘Calculate’ button.
3. View the results and chart below the calculator.

The pan evaporation (E_p) can be calculated using the following formula:

E_p = E_0 * (1 + W * (U – U_0)) * (1 + H * (RH – RH_0))

Where:

• E_0 is the reference evaporation (mm/day),
• W is the wind factor,
• U is the wind speed (km/h),
• U_0 is the reference wind speed (km/h),
• H is the humidity factor,
• RH is the relative humidity (%),
• RH_0 is the reference relative humidity (%).

Pan Evaporation Data (mm/day)

Month	Temperature (°C)	Wind Speed (km/h)	Relative Humidity (%)	Pan Evaporation (mm/day)

Comparison of Pan Evaporation Methods

Method	E_0 (mm/day)	W	U_0 (km/h)	H	RH_0 (%)

• Always use a standard 12-inch diameter pan for consistent results.
• Ensure the pan is level and not shaded by surrounding vegetation.
• Record and track data regularly for accurate long-term averages.

1. Consider using a pan evaporation gauge for automated and more frequent measurements.
2. Consult local meteorological services for regional-specific pan evaporation data.

What is the difference between pan evaporation and potential evaporation?

Pan evaporation is a measured value, while potential evaporation is a theoretical maximum based on atmospheric conditions.

USGS Guide to Pan Evaporation

FAO Irrigation and Drainage Paper 56: Pan Evaporation