University of Florida

Turfgrass Evapotranspiration (ETc)

Consumptive use of water, or evapotranspiration (ETc), the total amount of water required by a crop for growing and development (transpiration) plus the amount of water lost from the soil surface (evaporation) (Beard and Kenna, 2008). It is different from potential evapotranspiration (ETo) which is defined as "the amount of water transpired in unit time by a short green crop, completely shading the ground, of uniform height and never short of water" (Penman, 1956). Most of the water transpired through the plant moves through openings in the leaves called stomates, whose primary benefit is the cooling effect resulting from the evaporation process.

The amount of water lost through the evapotranspiration process by turfgrasses depends on several environmental factors, such as soil moisture, temperature, solar radiation, humidity and wind velocity. Turfgrass evapotranspiration rates are higher in arid climates than in humid climates because of the greater water vapor deficit between the leaf and the atmosphere in dry air (Duble, 2006). High rates of evapotranspiration are also observed under well-watered conditions, whereas low rates are associated with water stress conditions. The evapotranspiration process continues to be of foremost importance in water resources planning and management and in irrigation development (Jensen et al., 1990).

Several methodologies available to determine crop evapotranspiration as well as some ETc rates for warm-season turfgrasses growing in Florida are described next.


Southwest Florida Water Management District