Evapotransipration is the process through which water evaporates and is released as water vapor into the atmosphere. This metric also takes into account water vapor produced by plants as a biproduct of photosynthesis. We estimate evapotranspiration using the Harmon (1963) method, which depends upon the average day length and the saturated vapor pressure, which itself is a function of the daily mean temperature. Actual evapotranspiration is estimated based on the surface water inputs (i.e. precipitation and outdoor water use) and open waters (i.e. estuary, ponds, and swimming pools).
Potential evapotranspiration = (715.5 * day length * saturated vapor pressure) / (average daily temperature + 273.2)
Used to calculate: impervious runoff from hardtops and pervious runoff from soil
Depends upon:
—Parameters: hours per day, temperature and water content of steam
—Other metrics: ecosystem area, residents, water used outside, water held on plants and rainfall