Some terminologies

a) Evapotranspiration: Evapotranspiration is the sum of the water lost to the atmosphere by the plants through transpiration and the water evaporated from the soil and water body surrounding the plants. It will eventually depend upon the available moisture for both the process of transpiration and evaporation.

b) Potential evapotranspiration (PET) & actual evapotranspiration: When sufficient moisture is freely available to completely meet the needs of vegetation fully covering an area, the resulting evapotranspiration is called potential evapotranspiration (PET).

c) Reference Evapotranspiration: The evapotranspiration rate from a reference surface, not short of water, is called the reference crop evapotranspiration or reference evapotranspiration.

d) Consumptive use: It refers to the total seasonal water loss from an area of land due to plant growth and evaporation usually being expressed in acre-feet.