Calculate potential evaporation with energy balance and atmospheric factors. Track results, tables, and plotted trends. Built for precise study, testing, and field comparison needs.
Potential evaporation is the amount of water that could evaporate when energy and atmospheric demand are available without strong moisture limits. It is often used in environmental physics, hydrology, irrigation planning, and land surface studies.
This page uses a radiation-based Priestley-Taylor style approach. It focuses on net radiation, air temperature, psychrometric effects, latent heat, and an adjustment coefficient. The result is useful for comparing conditions across days, sites, or experimental scenarios.
1) Saturation vapor pressure:
es = 0.6108 × exp((17.27 × T) / (T + 237.3))
2) Slope of saturation vapor pressure curve:
Δ = 4098 × es / (T + 237.3)²
3) Daily potential evaporation:
PE = α × [Δ / (Δ + γ)] × (Rn / λ)
4) Total evaporation over the selected period:
Total PE = Daily PE × Days
Here, Rn is net radiation, T is air temperature, γ is the psychrometric constant, α is the Priestley-Taylor coefficient, and λ is latent heat of vaporization.
| Case | Net Radiation | Air Temp | γ | α | λ | Computed Δ | Daily PE |
|---|---|---|---|---|---|---|---|
| 1 | 8.00 | 18.00 | 0.066 | 1.26 | 2.45 | 0.1298 | 2.7272 |
| 2 | 12.00 | 22.00 | 0.066 | 1.26 | 2.45 | 0.1611 | 4.3782 |
| 3 | 16.00 | 26.00 | 0.066 | 1.26 | 2.45 | 0.1987 | 6.1769 |
| 4 | 20.00 | 30.00 | 0.066 | 1.26 | 2.45 | 0.2434 | 8.0913 |
It estimates how much water could evaporate when enough energy is available and surface moisture is not the limiting factor. It reflects atmospheric demand rather than actual observed loss alone.
Net radiation supplies the main energy driving phase change. When radiation rises, the energy available for evaporation usually increases, so the potential evaporation estimate also grows.
Temperature affects saturation vapor pressure and its slope. Those values influence how strongly available energy translates into evaporation in the Priestley-Taylor style formulation.
It links air pressure, heat capacity, and latent heat effects. In practice, it helps balance the energy term with atmospheric thermodynamic behavior in evaporation equations.
Use it when you already derived the slope of the saturation vapor pressure curve from another trusted workflow or dataset and want the calculator to follow that exact value.
A common value is 1.26 for moist surfaces in radiation-based applications. Still, your research method, calibration approach, or site condition may justify another coefficient.
No. Potential evaporation shows the atmospheric demand under favorable moisture conditions. Actual evaporation can be lower when water supply, vegetation, or surface resistance limits loss.
The calculator returns millimeters per day for the daily estimate and millimeters across the selected period for the total estimate, assuming the entered units follow the shown labels.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.