I was thinking about how to do some climate engineering of Australia or Africa, and came up with a megastructure to do it.

I was thinking of putting several hundred square miles of something dark (black felt or something similar maybe) in the ocean just upwind of a region. The goal is to concentrate solar energy near the surface.

Increased evaporation would increase air humidity, and rain downwind would increase a lot. Seemed like the lowest tech, lowest cost way to convert solar into rain/fresh water on a massive scale.