Trees produce the most "rainfall", and shrubs are next. How
Rainfall is Increased by Planting Trees and Shrubs.
Trees Create Rain.
Trees, and shrubs release water vapor (transpiration) from all parts, mostly through the leaf pores (stomata) and some of that water, condenses back into liquid water, drops back on and into the plant, and some extra rolls off the plant and onto/into the soil/mulch. This is a different form of rain, but it is still rain!
Plants Catch Water From the Tule
Fog, and More Rain is Produced
For several months every year, the San Joaquin Valley is covered by the tule fog, which hangs so low, and is so thick, that when you are driving a car, you cannot see the white line in the middle of the road, barely see the road itself, or even the edge of the road! Every 24 hours, the water that is in tiny droplets in the tule fog, contacts the leaves of the trees and shrubs and drips off the leaves and onto the ground. All together, trees, and shrubs, can significantly increase effective rainfall in a region. Generally, the taller and wider the tree, the more moisture it catches, and the more "rain" it produces! It also catches nutrients (ammonium, sulfate, nitrate) in the air, via the water vapor, that helps to acidify an alkaline soil. More "rain" from the plants-and-tule fog combination! This "rain" also may contain lower levels of alkali salts than the irrigation water!
How Planting Trees Helps the Land
Deep-rooted trees and shrubs: allow the soil to hold more moisture,
increase nutrients in the soil, decrease pH (make alkaline soils more
acidic), decrease soil EC (electrical conductivity) and decrease sodium
levels in the soil. Neighboring trees outermost leaves should touch
each other (canopy closure) for best results.
Vegetation Change = Rainfall Change
Researchers have discovered, much to their dismay, that when trees, are removed from an area, the rainfall drops in half!! and soil alkalinity increases! This means, if the measured rainfall in a region with the natural component of trees and shrubs, was 5 inches/year, in reality it was actually closer to 10 inches/year, adding in the water that drips from trees and shrubs (which is not caught in a rain gauge). If trees were then removed the rainfall would go from 10 inches/year down to truly 5 inches/year. Trees and shrubs make rain, and decrease alkali salts in soil!