Water Measured From the Sky

Water management is serious business in the American West, where precipitation is scarce, irrigated agriculture is a major industry, new housing subdivisions spread across arid landscapes and water rights are allocated in a complicated seniority system. "If you can't measure it, you can't manage it," water officials are fond of saying. But measurement -- trying to determine how much water is diverted from rivers and how much is pumped from hundreds of thousands of wells -- has been an inexact and expensive science. Now a tool developed by the Idaho Department of Water Resources and the University of Idaho is changing the face of water management and conservation by efficiently offering specific measurements of the water consumed across a large region or single field. Using surface temperature readings from government satellites, air temperature and a system of algorithms, the new method lets officials measure how much water is "consumed" on a certain piece of land through evapotranspiration. Evapotranspiration is a combination of the evaporation of water into the atmosphere and the water vapor released by plants through respiration -- basically, a measurement of the water that leaves the land for the atmosphere, not water that is diverted or pumped onto land but then returned quickly to the water table or river for other users. Water resource management agencies in Idaho and other states see this as the best way to measure water consumption, since it is a more exact definition of how much water is being removed from the system by a given individual or entity...WPost