This is a really good episode, and I strongly recommend it. It features Andrew's coverage of and participation in the "Great Green Wall" in Africa.
The Great Green Wall features water harvesting structures, combined with planting of both grasses and trees.
This video of Andrew's has received 1,600,000 views--by far his most popular video--and it is easy to understand why.
Andrew calls this the Great Green Wall 2.0, because the first iteration featured failed tree planting projects with high tree mortality. Now they have more of an ecological understanding of what really works, where water harvesting works in conjunction with native plant communities. This also works in conjunction with people's need for food, by providing food for both people and livestock. That way, everyone is incentivized to support the projects.
I was surprised to learn that the Sahel region includes 30,000,000 nomadic herding people. Somehow, as Andrew reports, they have figured out how to make peace between the herders and the farmers, partly by figuring out how the camels, etc. can get water without trampling crops and fences.