Evapotranspiration Calculator
Estimate reference evapotranspiration (ET₀) using a simplified Penman-Monteith approach from temperature, humidity, wind speed, and solar radiation.
Inputs
Results
Daily ET₀
5.16 mm/day
Weekly ET₀
36.1 mm/week
How to Use This Calculator
- Enter Mean Temperature, Relative Humidity, and Wind Speed.
- Set Solar Radiation.
- Review Daily ET₀ (mm/day) and Weekly ET₀ (mm/week).
- Use Monthly ET₀ (mm/month) and Annual ET₀ (est.) (mm/yr) to inform your decision.
- Use the chart to visualize the results and explore different scenarios by adjusting inputs.
How the result changes with Solar Radiation
| Solar Radiation | Daily ET₀ | Weekly ET₀ |
|---|---|---|
| 5.4 | 2.94 mm/day | 20.57 mm/week |
| 16 | 4.55 mm/day | 31.84 mm/week |
| 30 | 6.68 mm/day | 46.73 mm/week |
| 41 | 8.35 mm/day | 58.43 mm/week |
What each input means
- Mean Temperature
- Average daily air temperature at 2 m height in degrees Celsius
- Relative Humidity
- Mean daily relative humidity as a percentage (lower humidity = higher ET)
- Wind Speed
- Average wind speed at 2 m height in meters per second
- Solar Radiation
- Incoming solar radiation (10-15 = cloudy/winter, 25-35 = clear summer day)
How this is calculated
Formula
ET₀ = [0.408ΔRn + γ(900/(T+273))u₂(es-ea)] / [Δ + γ(1+0.34u₂)]Worked example, using the default values
- Identify Input Parameters4 parametersMean Temperature = 25, Relative Humidity = 50, Wind Speed = 2, Solar Radiation = 20 = 4 input(s) provided
- Calculate Daily ET₀Daily ET₀5.16 = 5.16
- Calculate Weekly ET₀Weekly ET₀36.1 = 36.1
- Calculate Monthly ET₀Monthly ET₀154.7 = 154.7
- Calculate Annual ET₀Annual ET₀1882 = 1882
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