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.