is the sum of evaporation
and plant transpiration
. Potential evapotranspiration is the amount of water that could be evaporated or transpired at a given temperature
, if there was plenty of water
available. Actual evapotranspiration can not be any greater than precipitation
, and will usually be less because some water will run off in rivers
and flow to the oceans
. If potential evapotranspiration is greater than actual precipitation, then soils are extremely dry during at least a major part of the year.