Seems like we should be testing geoengineering in deserts first before we try it in much harsher environments like Mars. I think desalinated ocean water via low tech solar might be a good way to start - https://inhabitat.com/wp-content/blogs.dir/1/files/2016/08/F...
My understanding is that desalinization should be a method of last resort, since it produces a lot of brine that is hard to deal with at scale in a way that isnt bad for the marine life. Depending on the desert, dew collectors might work, although I havent looked into how much water sphagnum moss needs over a year, now much a dew collector can produce, how much evaporation would happen, etc.
