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Suppose we create thousands of these tunnels in the Sahel countries. That would be combating desertification at its best. And we would create a fantastic carbon sink !
Maybe a suggestion for the Great Green Wall : why not using the drought-tolerant Navajo willow (Salix matsudana var. Navajo) for setting up a maximum of these tunnels, in which people could also grow their own fresh food ?
It would be killing several birds with one stone.
Don’t let me preach in the desert ! Just try it !