Environmental Engineering Reference
In-Depth Information
reached the ground surface. This effect is greatest when the rainfall is light and the leaf
density high. Small quantities of moisture may flow down the stems of the plants, but
with heavy or prolonged
Figure 8.7
The hydrological cascade in a soil - plant -
atmosphere system.
Source: After Oke (1987).
rain some droplets will fall right through the crop to moisten the soil surface, eventually
reaching the plant roots.
The output of the system is primarily through transpiration from the leaves and
evaporation from both soil and leaves. Moisture is extracted from the soil to maintain
transpiration, but if the soil becomes too dry during droughts the plants may wilt or even
die. During periods of rain, input is usually far higher than evapotranspiration alone. This
surplus goes to recharge moisture in the soil or it becomes run-off - the horizontal flow
of moisture on the soil - which eventually forms part of the river system.
THE MICROCLIMATE OF WOODLAND
So far we have been dealing with the microclimate either on, or at least close to, the
ground surface. From it we have been able to illustrate the processes controlling the
climate at that level. As the crop or vegetation gets larger, so the degree of modification
