Start / Water and irrigation / Crop water demand
Estimate how much water the atmosphere takes from a reference lawn per day, using only temperature and latitude.
Pre-sizing and estimating tool: the results do not replace a design, calculation, or report signed by a qualified professional, nor verification against the applicable standards.
Reference evapotranspiration for each month, with the same temperatures; the highlighted bar is the month of the day entered.
ET₀ for different ranges, with the same average temperature; the point is your day.
Drag the controls to simulate data different from what you entered (from 30% less to 30% more) and watch the result change instantly.
ET₀ for the same day with colder and hotter temperatures, and with different temperature ranges.
The calculation done in steps, with the values you entered.
The calculation memo gathers this page's inputs, results, equations, assumptions, and references, with fields for project, responsible person, and review. The full report also includes the charts and interpretations, in color. In the print window, choose Save as PDF.
Enter the site's latitude (negative in the Southern Hemisphere), the day of the year, and the maximum and minimum temperatures. The calculator estimates ET₀ and shows the radiation at the top of the atmosphere.
Latitude −13°, day 180 (end of June), maximum 31 °C and minimum 21 °C.
Ra about 27.6 MJ/m²/day, or 11.3 mm/day. Mean = 26 °C. ET₀ = 0.0023 × 11.3 × (26 + 17.8) × √10 = about 3.6 mm/day.
Because latitude and time of year determine how much radiation reaches the top of the atmosphere. In summer, at low latitudes, radiation is higher.
It is the crop coefficient: it relates ET₀ to the crop’s actual need at each stage. Use the reference value for the crop and stage.
Yes, to estimate the typical ET₀ for the month. For irrigation interval decisions, use daily values or data from the nearest station.
It works best in climates similar to those where it was calibrated. In humid places or with strong wind, the result tends to underestimate.
Important notice: the Agrocalcs tools make estimates and preliminary sizing based on the data entered and on published engineering methods. They do not replace a design, a calculation report or a report signed by a qualified professional (CREA/ART), nor verification against the applicable technical standards and legislation, such as the Regulatory Standards of the Ministry of Labor. Material and fuel properties vary: check with the manufacturer or with analyses of your process before deciding. By using the site, you agree to the Terms of Use.
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