Evapotranspiration is nothing but the combination of evaporation and transpiration. Evaporation accounts for the movement of water to the air from sources like soil, canopy interception and waterbodies.
Transpiration accounts for the movement of water within the plant and the subsequent loss of water as vapor through the stomata.
Factors affecting evapotranspiration are:
soil cover,
solar radiation,
humidity,
temperature, and
wind.