Evaporation and Transpiration
Much of the water that soaks into the soil from irrigation or rain ultimately returns the the atmosphere as water vapor through direct evaporation from the surface or by transpiration through plant leaves as the plants use the water for growth and seed production. This loss cools the surface and plant canopy just like the evaporation of sweat cools our skin. A cool field in an arid area indicates water use by irrigation.
Using the surface temperatures measured by satellites, and some additional information, water resource managers can determine the rate at which water is used in a farm field.
This animation illustrates the process of evapotranspiration. As water soaks into the ground, some is taken up by plants and some evaporates out of the soil. The plant leaves transpire some of the water they picked up. Both processes, together known as evapotranspiration, end up cooling the surface the water excapes from as it returns to the atmosphere.
Please give credit for this item to:
NASA/Goddard Space Flight Center Conceptual Image Lab