We could, as a human race, accept that climate change is real and something that needs to be tackled. Whether it's influenced by humans or not, it's still very much a problem and something that needs to be studied and have solutions found. We have the collective intelligence to do it, we just need to put forth the effort and fund it appropriately. I'm of the mind that humans do influence climate change,. but I also accept that some of it are likely due to the cycles of the Earth. It's an easier time to address the human element, so we should probably start there.
As for water, it's imperative that we come up with an efficient, cost-effective way to desalinize water. Build these plants along the coast and pipe the water where it needs to be. If we can send oil thousands of miles without issue, we can do so with water.
Power production needs to switch to make use of these new conditions. The west has gigantic areas with nothing in them that are hot, sunny, and dry. Build solar power stations there and use them to power the cities instead of relying on fossil fuels. Here in Salt Lake, the lake itself could easily support a nuclear power station too.
Areas in drought conditions need to take a good hard look at their industries too. Here in Utah, we grow alfalfa, which is one of the thirstiest crops making it extremely water-intensive. We don't have the water to sustain that, nor do we have the water to sustain huge cattle herds. We need to switch to a less water-intensive crop and probably switch to chickens or something for livestock. I get that you can't just ask farmers to quit farming, but you can make it prohibitively expensive for them to grow water-intensive crops. What's even worse is that a majority of our alfalfa doesn't even make it into the stomachs of American cows. It gets shipped to Asia since the quality of it sucks. Unfortunately, Gov Cox is an alfalfa farmer and wouldn't dream of doing anything to upset his homies.
Assuming none of that works, then the US government really needs to figure out a way to relocate people over the next 100 years.