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Evapotranspiratie Calculator

Referentie-ET0 via de Hargreaves-Samani-vergelijking.

Inleiding

Evapotranspiration Calculator — Reference ET0 via the Hargreaves-Samani equation. Enter Mean temp (°C), Max temp (°C), Min temp (°C), Extraterrestrial radiation Ra (mm/day equiv.) to get an instant, accurate result.

Formule

Simplified Hargreaves-Samani (1985) equation: ET0 (mm/day) = 0.0023 × (Tmean + 17.8) × √(Tmax − Tmin) × Ra, where Ra is extraterrestrial radiation entered directly in mm/day water-equivalent. This is a temperature-only estimate of reference evapotranspiration; the full Penman-Monteith method (the FAO-56 standard) additionally requires wind speed, humidity, and measured solar radiation and is not implemented here.

Stap voor stap

  1. Enter the Mean temp (°C).
  2. Enter the Max temp (°C).
  3. Enter the Min temp (°C).
  4. Enter the Extraterrestrial radiation Ra (mm/day equiv.).
  5. Click Calculate to see your result instantly.

Praktijkvoorbeeld

Example: With Mean temp (°C) = 20 °C, Max temp (°C) = 28 °C, Min temp (°C) = 14 °C, Extraterrestrial radiation Ra (mm/day equiv.) = 15, the Evapotranspiration Calculator gives Et0 Mm Day: 4.8795.

Veelgestelde Vragen

Why do I have to enter Ra myself instead of a location?
Extraterrestrial radiation depends on latitude and day of year through solar geometry calculations that this simplified tool does not model, so it is accepted as a direct input — you can look it up from standard Ra tables for your latitude and month.
How accurate is Hargreaves-Samani compared to Penman-Monteith?
It is a widely used, lower-data-requirement approximation that is generally reasonable for planning purposes, but Penman-Monteith is considered the more accurate reference method when full weather-station data is available.
What inputs does the Evapotranspiration Calculator need?
You'll need to provide: Mean temp (°C), Max temp (°C), Min temp (°C), Extraterrestrial radiation Ra (mm/day equiv.). All fields use sensible defaults, so you can see a working example immediately and then adjust the values to match your own numbers.
How accurate is the Evapotranspiration Calculator?
The Evapotranspiration Calculator applies the formula exactly as calculated — Simplified Hargreaves-Samani (1985) equation: ET0 (mm/day) = 0.0023 × (Tmean + 17.8) × √(Tmax − Tmin) × Ra, where Ra is extraterrestrial radiation entered directly in mm/day water-equivalent. This is a temperature-only estimate of reference evapotranspiration; the full Penman-Monteith method (the FAO-56 standard) additionally requires wind speed, humidity, and measured solar radiation and is not implemented here. — so results are precise for the inputs you provide. Accuracy depends on entering correct, realistic input values.
Is the Evapotranspiration Calculator free to use?
Yes, the Evapotranspiration Calculator is completely free, requires no signup, and runs instantly in your browser.

Over Evapotranspiratie Calculator

The Evapotranspiration Calculator uses a real, verifiable formula — Simplified Hargreaves-Samani (1985) equation: ET0 (mm/day) = 0.0023 × (Tmean + 17.8) × √(Tmax − Tmin) × Ra, where Ra is extraterrestrial radiation entered directly in mm/day water-equivalent. This is a temperature-only estimate of reference evapotranspiration; the full Penman-Monteith method (the FAO-56 standard) additionally requires wind speed, humidity, and measured solar radiation and is not implemented here. — so results are accurate every time, not an approximation.