Irrigation Flow Calculator

Irrigation flow rate: sizing water demand

Flow rate per hectare comes from Q (L/h) = ETc · area / efficiency. Here ETc is the crop evapotranspiration in mm/day, the area is in m², and efficiency is the system's loss factor. In Brazil, ETc tends to sit near 5 mm/day through summer for most annual crops. Efficiency depends heavily on the method you pick. A center pivot runs 70–80%, a conventional sprinkler 65–75%, and drip irrigation clears 90%. Take 1 ha (10,000 m²) with ETc = 5 mm/day on an 80% pivot: that works out to 50,000 L/day / 0.8 = 62,500 L/day. Switch to localized drip and the number drops about 15%, since you lose nothing to wind drift or evaporation off wet soil.

Applications

It shows up in precision agriculture work, EMBRAPA water-management guidance, and water-grant requests filed under Lei 9.433/1997 (Política Nacional de Recursos Hídricos). Engineers also lean on it to size pumps and pipes, and to lay out the irrigation schedule once the dry season hits.

FAQ

How do I measure ETc? Take the reference evapotranspiration (ET0, pulled from a weather station) and multiply it by the crop coefficient (Kc). Kc shifts as the plant moves through its growth stages.

Why does drip beat pivot? Because it puts water right at the root zone, where almost nothing is lost to evaporation or wind. That pushes the effective fraction up toward 95%.

Do I need a water grant? In Brazil, once a catchment goes past the state's insignificant-use threshold (usually around 1 L/s), you need an outorga from ANA or the state water agency.