> If you tame the flash flood [3][5], you can change deserts

This is very hyperbolic. Yes it is helpful but desert are deserts.

Californians have been planting and watering huge in-land areas for decades. All these areas have reverted to pure desert every time there is a drought and water quotas.

Reforestation (and saving the rain forests) are x10 easier and cheaper in rainy regions !!!