Four physical factors determine water use by plants

There are four factors determining evapotranspiration of landscape and turf plants, or any plants.  The factors are radiant energy, wind, temperature, and relative humidity (or more precisely, the difference in the vapor density between the interior of the leaf and the air above the canopy).  Surveys have shown that most of the variability in evapotranspiration among observations within a region is explained by differences in radiant energy and wind.