What is Evapotranspiration?

Evapotranspiration refers to the combined loss of water from a vegetative surface through both plant transpiration and soil evaporation. Daily evapotranspiration figures are generated by weather stations combining the effects of solar radiation, temperature, wind and humidity to estimate crop water use. Evapotranspiration is measured in millimeters (mm).

Reference Evapotranspiration (Eto)

Reference evapotranspiration (Eto) figures represent an estimate of the water used by a healthy, well-watered, full cover grass surface. It provides a standard method to compare water use across a range of crop types and locations.

Crop coefficients (Kc) for winegrapes

Most horticultural crops do not fully cover the ground, and the Eto figure needs to be adjusted by a crop coefficient (Kc) in order to estimate the crop evapotranspiration (Etc). Crop coefficients are a set of numbers that reflect the crop being grown and the developing canopy. These adjustments have been made in the following graphic to estimate recent and future winegrape water requirements at Mildura and Swan Hill. This knowledge can assist winegrape growers with their irrigation management.

The table below is the set of Kc values used in these calculations. They represent moderate vigour winegrapes.  Kc values will vary slightly with winegrape variety, growth stage, crop load, canopy size, rootstock, soil type and row spacing.