5.1. Do forests have an effect on climate?
The importance of forests on global climate is relatively
moderate compared to changes in the polar ice caps, in the temperature
of oceans and in the transmission of sunlight and heat from the
surface of the earth. Since two thirds of the surface of the globe
is covered by oceans and polar ice caps, these have the most significant
impact on climate. More...
5.1.1. Forests do have an effect on rainfall. Although
on a global scale the main source of water vapor is the surface
of the oceans, evaporation from land surfaces, including forests,
can be important regionally. In the Mississipi Valley, ‘recycled’
land water was found to account for one third of the average precipitation,
whereas in the Amazon forest it accounted for one half. More...
5.1.2. The foliage of the canopy intercepts falling rain
and thereby regulates cycles of water flow (into rivers, soils,
underground reserves, etc.). Variables such as the foliage density
or the soil composition make it difficult to state whether forests
increase or decrease water flow. It is clear however that forests
help reduce the severity of tropical rainstorms and rapid snowmelt,
thus mitigating floods and ensuring a more steady water flow. Forest
cover does this by producing litter that protects the soil and allows
more water to seep into the ground. If this protection is decreased
because of logging or fires, it can lead to increased overland flow,
which is quicker to reach and flood rivers. Hydrological processes
however are complicated and involve many factors. More...