Using the Mississippi River as a dividing line, the eastern U.S. is wet, the western U.S. is dry (see map of mean annual precipitation here).
The American West is dependent on rivers, fed by mountain snowmelt, and its economy depends heavily on reclamation projects involving the damming of rivers. An excellent book on that subject is this one.
The West has three major river basins, two of them named after states: The Columbia, Missouri, and Colorado.
The Colorado waters the driest and most river-dependent region: The desert southwest (map here). It’s the watercourse that carved the Grand Canyon. Phoenix and Las Vegas draw their water supplies from it, as does California’s agriculturally lush Imperial Valley (described here). Wikipedia says (here),
“[T]he Colorado River and its tributaries are a vital source of water for 40 million people. The river and its tributaries are controlled by an extensive system of dams, reservoirs, and aqueducts, which in most years divert its entire flow for agricultural irrigation and domestic water supply. Its large flow and steep gradient are used for generating hydroelectric power, and its major dams regulate peaking power demands in much of the Intermountain West.”
(The “Intermountain West” is explained here.)
The Colorado River’s water is divided up under a complex set of agreements, called the Colorado River Compact (details here), and is fully appropriated, meaning all of it is being used, to the point where none reaches the ocean. There’s not one drop to spare, and when the flow shrinks, something has to give.
The flow is shrinking because of a years-long drought attributable to climate change. There’s simply less snow falling on the mountains. For a while, the shortage was made up by drawing down the reservoirs behind the dams. But now, something has to give. And just did.
“The federal government on Monday declared a water shortage on the Colorado River for the first time, triggering mandatory water consumption cuts for states in the Southwest,” CNN reported on August 16, 2021 (story here). The cuts will go into effect on January 1, 2022.
‘”It’s very significant,’ Brad Udall, senior water and climate scientist at Colorado State University, told CNN. ‘It’s something that those of us in the climate community have been worried about for over a decade, based on declining flows due to climate change.'”
“Under the complex priority system, Arizona and Nevada will be affected by the tier-1 shortage,” CNN said. “Arizona will see an 18% reduction in the state’s total Colorado River supply, primarily impacting agriculture.” Nevada’s allocation will be reduced by 7% next year. Further cuts could come in 2023.
The southwest has seen rapid urban growth in recent years. I’d be leery of moving to a place like Phoenix or Las Vegas. Ironically, residents of these “dry” cities enjoy the West’s lowest municipal water rates, while the “wet” cities of Portland and Seattle sock their residents with the highest rates. But Phoenix is rated at “extreme risk” of water scarcity; the taps may not go dry, but climate change “is making water shortages ever more likely in the West’s most populous places” (see story here).
Those shortages will fall hardest on farmers and ranchers (see story here). Even though cities use a lot of water, agriculture sponges up far more. About 90% of Colorado River water goes to irrigation. It follows they will suffer the brunt of allocation cuts. It will put some of them out of business.