SUMMARY
Let us now be clear about how trees affect total precipitation. The case taken is where winds blow inland from an ocean or large lake:
1. The water in the air is that evaporated from the surface of the sea or lake. In contains a few salt particles but is 'clean'. A small proportion may fall as rain (1520%), but most of this water is CONDENSED out of clear night air or fogs by the cool surfaces of leaves (8085%). Of this condensate, 15% evaporates by day and 50% is transpired. The rest enters the groundwater. Thus trees are responsible for more water in streams than the rainfall alone provides.
2. Of the rain that falls, 25% again re-evaporates from crown leaves, and 50% is transpired. This moisture is added to clouds, which are now at least 50% 'tree water'. These clouds travel on inland to rain again. Thus trees may double or multiply rainfall itself by this process, which can be repeated many times over extensive forested plains or foothills.
3. As the air rises inland, the precipitation and condensation increases, and moss forests plus standing cluods may form in mountains, adding considerably to total precipitation and infiltration to the slower slopes and streams.
4. Whenever winds pass over tree lines or forest edges of 12 metres (40 feet) or more in height, Eckman spirals develop, adding 40% or so to rainfall in bands which roughly parallel the tree lines.
5. Within the forest, 40% of the incident air mass may enter and either lose water or be rehumidified.
6. And in every case, rain is more likely to fall as a result of organic particles forming nucleii for condensation, whereas industrial aerosols are too small to cause rain and instead produce dry, cloudy conditions.
Thus, if we clear the forest, what is left but dust?
Works at a residential alternative high school in the Himalayas SECMOL.org . "Back home" is Cape Cod, E Coast USA.
Come join me at www.peacockorchard.com
Be the Mr. Rogers of your neighborhood. This tiny ad will help you:
Lazy Ass Gardening by Robert Kourik
https://permies.com/w/lazy-ass-gardening
|