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Water lost to the atmosphere through evapotranspiration (ET; soil evaporation + canopy transpiration) serves to cool the Earth's surface. Just as a thermometer is used to diagnose stress in the human body, land surface temperature (LST) derived from remote sensing data in the thermalinfrared (TIR) band (8–14 microns) is a valuable diagnostic of biospheric stress resulting from soil moisture deficiencies. Soil surface temperature increases with decreasing water content, while moisture depletion in the plant root zone leads to stomatal closure, reduced transpiration, and elevated canopy temperatures that can be effectively detected from space. In land surface modeling, TIR imagery can serve as an effective substitute for precipitation data, providing much needed water information in data-poor regions of the world.