Evapotranspiration (ET) is a measure of the amount of moisture lost to the atmosphere through evaporation from the ground and transpiration from plants. ET values can be used for determining irrigation required by estimating how much moisture is being lost.

There are several methods for calculating ET, some requiring more parameters than others. WIN calculates ET using the Priestley-Taylor method which uses a minimum number of parameters.

The following prototype ET map was generated from data collected from weather stations within the selected zones. The map shows the millimetres of moisture lost to evapotranspiration on the given day.