Environmental Engineering Reference
In-Depth Information
regulate water loss from the plant. Many factors influence evapotran-
spiration, but the most important are humidity, temperature, wind and
canopy resistance (Fig. 7.1).
Humidity
Water loss from the plant occurs because of the gradient that exists
between the water-saturated cells and the moisture in the surrounding
air. In drier air, the gradient is steeper and water is therefore lost faster.
As would be expected, the highest evapotranspiration rates are in arid
climates, where the humidity is the lowest.
Temperature
Increasing temperature directly accelerates evaporation, but temperat-
ure's effect on transpiration is more complex. Initially, leaves transpire
more in order to cool themselves down, but when temperature rises too
high, partial closure of the stomata can be triggered in order to conserve
water. Turf-grasses adapted to the tropics use this type of physiological
defence less than do cool-season turf-grasses, and unless the temperature
is very high, they increase their evapotranspiration when the tempera-
ture rises.
Evapotranspiration (ET)
Canopy resistance
Transpiration
from plants
Environment
humidity
temperature
wind
Management
mowing height
fertility
Evaporation
from soil
Fig. 7.1. Factors influencing evapotranspiration of turf.