Long, informative, definitely worth a read - and depressing.
If natural climate fails to deliver water, and neigbours claw away what they can while it's upstream - this means either desalination, condensing water out of air (I would prefer if this technology was needed on Mars)... or just retreating from a place where nothing worthwhile can be done.
Both desalination and condensation tend to be incredibly energy-intensive, which limits their use. It's going to take solar getting a bunch cheaper before we see them used at scale for irrigation