What causes changes in evapotranspiration (ET)?

Reference evapotranspiration (ETo) is calculated by an equation. The Penman-Monteith equation is the standard equation used. The calculations shown in this chart were made using the FAO Penman-Monteith equation.

To calculate ETo, variables such as date, solar radiation, elevation, latitude, high and low air temperatures, humidty, and wind speed go into the equation. The equation then returns the ETo, which when calculated on a daily basis has units of mm/day (or inches/day). The ETo is calculated for a hypothetical reference…