The US Department of Defense is one of the only organizations that takes a strategic look at the effects of climate change, and they are flat-out in a tizzy about it. (Side-glance to KB, for links to evidence...)
I fully expect, that before I die - sometime in the next 40 years - that I will have fortified my home, and will have strangers living in my yard.
They may be people from Phoenix, or Nevada, or Mexico, or Central American countries. But they will be there, because their homes became uninhabitable due to drought, weather, food, dust-bowl conditions, etc. They had to leave, to survive.
The migrant caravans will move north, ignoring borders and laws. Because when millions of people come walking into your town, the police are going to be entirely powerless against them. (CUT TO: scene of Walking Dead zombies shambling towards the camera)
Phoenix has no plan for when it runs out of water, in a couple of years.
LA's power infrastructure can't support sustained periods of 113 degrees, like they had this year.
Normal people cannot survive without the support of a fully-functioning city... flushing toilets, on-demand water from the tap, police and health services, food, etc. So the Climate Migrants won't be moving to the Sierra Nevadas and national parks and setting up Little House On The Prairie-kinds of existences, because they don't have the skills.
They will move to the big cities. Who are already taxed to the limit, and can't sustain an influx of hundreds of thousands of people. So a few will stay (couple of million), and the rest will continue on the road.
The Great American Migrant Caravan.
In my lifetime. I'll bet on it.
Well let's talk about this.
As far as conflict, nowaypablo probably has hella better knowledge about doctrine at this point considering he's at West Point learning how to win wars and influence geopolitics'n'shit. Here's a useful link, and a lengthy discussion, we had years ago:
As far as water, nobody read this for some dumb reason and it's poignant as hell:
Because here's the thing: it's not like the Ogalala makes a giant slurping sound and six weeks later we're settling scores in Thunderdome. What happens is food gets more expensive, land in the Southwest gets cheaper, quality of life goes down and people of means leave. People without means mostly die.
The Syrian Civil War was precipitated by a drought. By extension, the Syrian refugee crisis was precipitated by climate change. And while there are definitely far-right populist parties arguing about the horrors of "(CUT TO: scene of Walking Dead zombies shambling towards the camera)", the fact of the matter is Europe absorbed a million refugees without major shocks to the system.
I met maybe a dozen people from New Orleans in 2006. They had nowhere to go back to so they packed up and left. One day they had a home, the next day they didn't. And really, that was orderly. The Mojavification of the Southwest is going to be more stark than New Orleans being destroyed but it's also going to be slower. It's going to be gradual. And it's going to be a case of straws and camels and people shedding northward in dribs and drabs until what's left in Castaic will be a lot like what's left in the Salton Sea.
You're not gonna have strangers in your yard. You're gonna have motor homes on your street. But shit, you might already.
There are two books about this future you might enjoy. The better one is Paolo Bacigalupi's The Water Knife. It is not a great book, but it could have been. The worse one is Clare Vaye Watkin's Gold Fame Citrus. It is a terrible book and would never have been any other. Bacigalupi builds up a world where water ceases to be available. It is a rich universe. Watkin builds up a world where water is suddenly gone. It is fucking stupid.