A heat dome is burning in Arizona and Nevada, where temperatures have climbed to over 115 degrees this week and doctors are warning that people can get third-degree burns from the crackling asphalt.

At Lake Mead, which supplies water to 25 million people in three southwestern states and Mexico, the water level has dropped to its lowest level since the reservoir was filled in the 1930s. In California, farmers are giving up their thirstiest crops to save others and communities are debating whether to ration tap water.

In Texas, power grids have come under pressure as residents crank up their air conditioners and utility companies ask their customers to turn off their appliances to avoid blackouts. Forest fires are raging in Arizona, Montana, and Utah.

And it’s not even summer yet.

“We are still a long way from the peak of the forest fire season and the peak of the dry season,” said Daniel Swain, climate scientist at the University of California at Los Angeles. “Things are likely to get worse before they get better.”

Global warming, fueled by fossil fuel burning, has been heating and drying up the American West for years. Now the region is boiling under a combination of a drought that’s the worst in two decades and a record-breaking heat wave.

“The southwest is being hit harder by climate change than almost any other part of the country, except perhaps coastal cities,” said Jonathan Overpeck, a climate scientist at the University of Michigan. “And as bad as it may seem today, it’s as good as it gets if we can’t get global warming under control.”

With temperatures expected to continue to rise as nations struggle to contain their global warming emissions, the western United States will face difficult and costly adaptation measures. This includes redesigning cities to withstand the heat, conserve water, and develop networks that won’t fail in extreme weather conditions.

This month has provided insights into whether states and cities are up to the task and has shown that they still have a lot to do.

From Montana to Southern California, much of the west suffers from unusually high temperatures. About 50 million Americans are being warned about heat warnings. Records have been set or broken in places like Palm Springs, Salt Lake City, and Billings, Montana.

As temperatures boiled 115 degrees in the Roosevelt Row arts district in Phoenix on Tuesday, Timothy Medina, 58, sat on a black metal platform 12 feet above the sidewalk finishing the blue lettering on a sign for a coffee shop. “It’s brutal – that heat against the wall,” he said. “Let me have a drink of the water.”

Construction workers, landscapers, and exterior painters like Mr. Medina have few options to endure the heat. He wore jeans so as not to burn his skin, along with a long-sleeved fluorescent yellow shirt and a $ 2 woven hat. But soon the heat won.

“I feel out of breath, tired,” he said.

Extreme heat is the clearest signal of global warming and the deadliest. Last year, the heat killed at least 323 people in Maricopa County, which includes Phoenix, a record by far.

Outdoor workers, the elderly, and anyone who does not have adequate protection or access to air conditioning are particularly at risk.

Across the country, heat waves are becoming more frequent, lasting, and happening earlier in the year, according to the Environmental Protection Agency. High heat in spring can be especially dangerous because it takes people by surprise, experts say.

Cities like Phoenix are struggling to keep up. While the city operates air-conditioned cooling centers, many were closed last year amid the pandemic. And making the centers accessible to all is a challenge.

Kayla and Richard Contreras, who sleep in a blue tent on a baking sidewalk at a homeless camp near downtown Phoenix, said the cooling centers are not an option because they have a dog and are concerned about keeping their belongings unattended in their tent allow.

They said she knew 10 homeless people who died in the heat last year.

Mr. Contreras, 47, fills water bottles from the spigots of houses he passes by. Ms. Contreras, 56, said she saves food stamps to buy popsicles on the hottest days. “That keeps us alive,” she said as she handed a friend an orange popsicle. “I feel like in hell.”

The sunset brings no relief. In Las Vegas, where the National Hockey League playoffs take place, forecasters expected the mercury to hit over 100 degrees on Wednesday night when the puck fell.

Last month, Phoenix City Council approved new $ 2.8 million climate spending, including the establishment of a four-person office for heat response and mitigation.

“This is a good start, but we are clearly not doing enough,” said David Hondula, an Arizona State University scientist who studies the effects of heat. A drastic reduction in heat deaths would require adding trees and shade in underserved neighborhoods and increasing funding to help residents who need help with energy bills or who lack air conditioning, among other things, he said.

“Each of those heat deaths should be preventable,” he said. “But it’s not just a technical problem. It means tackling difficult issues like poverty or homelessness. And the numbers suggest that we are going in the wrong direction. At the moment the heat deaths are increasing faster than population growth and aging. “

Strong heat waves also pose a challenge to the power grids, especially if the operators do not plan for them. Rising temperatures can reduce the efficiency of fossil fuel generators, transmission lines and even solar panels just as demand increases.

This week, the Texas power grid had reached its limits as electricity demand hit a June record while several power plants were offline for repairs. Network operators urged Texans to keep their thermostats at 78 degrees to save electricity.

Victor Puente, 47, stood in the shade of the porch of his blue wooden house in Pueblo de Palmas, outside the border town of McAllen, Texas, Tuesday. He said he tries to turn off his air conditioning during the day to save energy so it is available for sleeping.

“The last thing we need is to lose power over long distances,” he said.

In California, where temperatures hit 110 degrees, the grid operator has warned it could face challenges this summer, in part because droughts have reduced the capacity of the state’s hydropower plants.

Andrew Dessler, a climate scientist at Texas A&M University, found that tensions in the lattice illustrate the nonlinear effects of climate change. “Most people may not notice that it gets a little hotter every year,” he said. “But then the temperature reaches a certain threshold and suddenly the network fails. There are a number of these thresholds that are built into our infrastructure. “

That spring, the American west was hit by a severe drought that stretched from the Pacific coast to the Great Basin and the desert southwest to the Rocky Mountains and the northern plains.

Droughts have long been a feature of the West. But global warming is making things worse as rising temperatures dry out the soils and use up the snowpack in the mountains that normally provides water in spring and summer. These parched soils, in turn, add to this week’s heat wave and create a more violent explosion than would otherwise.

“It’s a vicious circle,” said Dr. Swain from UCLA

Arid conditions also suggest a potentially devastating fire season coming a year after the unusually devastating flames hit California, Oregon, and Colorado.

The drought has tightened water supplies across the west and shrunk reservoirs. In a California lake, the water became so shallow that officials identified the wreckage of an airplane that crashed into the lake in 1986.

The Inverness Public Utility District in Marin County, Calif., Will vote next week on whether to introduce rationing for 1,100 customers, allocating a certain amount of water to each household. It would be a first for the city, which last July called on residents to stop washing cars and filling swimming pools.

The drought has forced farmers to take drastic measures. Sheep and cattle breeders are selling this year’s herds months earlier, and some dairy farmers are selling their cows instead of raising the 50 liters of water that each animal uses each day. Farmers plant fractions of their usual amount or leave part of their land fallow.

“We went through droughts. This is one of the driest we can remember, ”said Dan Errotabere, 66, whose family has grown fruits, vegetables and nuts near Fresno for a century. It keeps 1,800 acres fallow and cuts down on garlic and tomatoes to divert water for almond and pistachio trees.

The impact on farms could lead to supply problems and higher prices nationwide, said Mike Wade, executive director of the California Farm Water Coalition. California produces two-thirds of the country’s fruit and one-third of its vegetables.

Many California farmers are already using micro-irrigation, drip hoses, and other water-saving methods. “We stretched every drop,” said Bill Diedrich, a fourth generation farmer in Fresno County.

Agricultural communities are at risk when the plants and trees die without water.

“When you run a long-standing family farm, you don’t want to be the one to lose it,” says Eric Bream, the third generation of his family to run a citrus farm in California’s Central Valley. Today he still has enough water. But “tomorrow everything could change in the blink of an eye.”

Elsewhere in the west, states are preparing for further cuts.

Lake Mead, which was created after the Hoover Dam was completed in 1935, has 36 percent capacity because the Colorado River’s outflows have declined faster than expected. The federal government is expected to declare a shortage this summer that would trigger a cut of about a fifth in water supplies to Arizona and a much smaller cut for Nevada starting next year.

Experts have long predicted this. The Colorado basin suffered from years of drought coupled with a steadily increasing consumption, as a result of population and economic growth as well as the expansion of agriculture, by far the largest water consumer in the west.

“We need to stop thinking of drought as a temporary thing,” said Felicia Marcus, visiting scholar on Stanford University’s Water in the West program.

Many cities have prepared. Tucson is one of the nation’s leading providers of wastewater recycling, treating more than 30 million gallons of gallons every day for irrigation or fire fighting. Cities and water districts in California are investing billions in infrastructure to store water in wet years to save it for droughts.

However, experts said there is a lot more that can be done, and it is likely costly.

“The Colorado River basin is ground zero for the effects of climate change on water supplies in the United States,” said Kevin Moran of the Environmental Defense Fund. “We have to plan for the river that climate scientists tell us we will likely have, not the one we want.”

Edgar Sandoval and Catrin Einhorn contributed to the reporting.