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Local water availability is permanently reduced after planting forests:
River flow is reduced in areas where forests have been planted and does not recover over time, a new study has shown. Rivers in some regions can completely disappear within a decade. This highlights the need to consider the impact on regional water availability, as well as the wider climate benefit, of tree-planting plans.
"Reforestation is an important part of tackling climate change, but we need to carefully consider the best places for it. In some places, changes to water availability will completely change the local cost-benefits of tree-planting programmes," said Laura Bentley, a plant scientist in the University of Cambridge Conservation Research Institute, and first author of the report.
Planting large areas of trees has been suggested as one of the best ways of reducing atmospheric carbon dioxide levels, since trees absorb and store this greenhouse gas as they grow. While it has long been known that planting trees reduces the amount of water flowing into nearby rivers, there has previously been no understanding of how this effect changes as forests age.
The study looked at 43 sites across the world where forests have been established, and used river flow as a measure of water availability in the region. It found that within five years of planting trees, river flow had reduced by an average of 25%. By 25 years, rivers had gone down by an average of 40% and in a few cases had dried up entirely. The biggest percentage reductions in water availability were in regions in Australia and South Africa.
Partial river flow recovery with forest age is rare in the decades following establishment (open, DOI: 10.1111/gcb.14954) (DX)
(Score: 5, Informative) by Booga1 on Friday January 31 2020, @03:06AM (3 children)
You're absolutely right on several points. Benefits go far beyond simple water table levels. The question becomes: what is the largest benefit in the long term?
Check out this scenario(emphasis mine): A Brazilian couple replanted 1,502-acre forest in 20 years and also gave a home to 500+ endangered plant & animal species. [stillunfold.com]
(Score: 2) by corey on Friday January 31 2020, @10:30PM
Thanks for posting that, I didn't know about them. Really interesting.
(Score: 0) by Anonymous Coward on Friday January 31 2020, @11:07PM (1 child)
"After Salgado’s forest was created, it resulted in even more rainfall in the area."
So wait, is it saying that planting trees results in more rainfall? Seems far fetched no?
(Score: 2) by Booga1 on Saturday February 01 2020, @12:34AM
Not as far fetched as it might seem at first. Remember, trees add turbulence to wind, forcing air to slow down over the forest. This directly contributes to increased rainfall.
Trees also slow down the runoff of water by adding debris to the forest floor that slows down runoff and keeps more water locally instead of feeding rivers. At the same time, trees recycle that water back out of the ground and into the air. See Joe's post [soylentnews.org] for a bit of a rundown on that in Florida.
That rain water isn't necessarily "new" water. In part, it's just recycled water being dropped back over the forest it came from instead of being swept out to a different area via river, Whether that's the ocean, a city, or a forest further away just depends on the location. The net result is that forests can influence their own weather, rain included.