They could always try to build some dams and save up water for emergencies like this instead of tearing them out.
You have to have river flows to dam up. That region has periods lasting centuries where river flows will be half to kne quarter what they were during the dam building era of the 1930s the Colorado river system has more dam capacity that it can possibly fill already it was built for 14 million acre feet per year the multi century avg flow of that river is half that value no amounts of dams will fix that. Desalination will be needed, both ocean water and saline groundwater desal will be needed