It requires large amounts of energy. Transpiration is the movement of water through a plant to the atmosphere. Scientists use the term evapotranspiration to describe both processes. The growth of crops is a function of water supply. If crops experience drought, yields are reduced.
Irrigation can supply crops with supplemental water.
By determining both actual evapotranspiration and potential evapotranspiration a farmer can calculate the irrigation water needs of their crops. The distribution of precipitation falling on the ground surface can be modified by the presence of vegetation. How much is intercepted is a function of the branching structure and leaf density of the vegetation. Some of the water that is intercepted never makes it to the ground surface. Instead, it evaporates from the vegetation surface directly back to the atmosphere.