What is behind the heatwave in the American West?

PHOENIX – Much of the American West has been ravaged by sweltering heat this week as a high-pressure dome combines with the worst drought in modern history to push temperatures into triple digits, breaking records before even the official start of summer.

Daily records were set this week in parts of Arizona, California, New Mexico, Montana, Wyoming and Utah. Phoenix, which bakes in some of the hottest weather in the western United States, is expected to hit 117 degrees (47 degrees Celsius) Thursday and 116 degrees Friday and Saturday.

“Very dangerous record heat is expected to continue today in the deserts with peaks well above normal,” staff of the National Weather Service in Phoenix wrote on Facebook. “A very good day to stay indoors.


The heat comes from a high pressure system over the west, a loop in the jet stream winds that move across the United States and vast swathes of soil sucked in by a historic drought, Marvin said. Percha, senior meteorologist for the Phoenix agency.

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He and other scientists say the heat wave is unusual because it happened earlier and lasts longer than most years.

“In June of last year, things looked pretty normal,” said Park Williams, a climate and fire specialist at the University of California, Los Angeles. “The record heat waves occurred in August and September. ”

But with such an early heat wave this year, “it could be the tip of the iceberg,” Williams said.


A two-decade drought that some scientists call a “mega-drought” sucked moisture from the soil across much of the western United States. The researchers said in a study published last year in the journal Science that man-made climate change linked to greenhouse gas emissions can be blamed for about half of the historic drought.

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Scientists who studied the dry spell that began in 2000 examined an area of ​​nine states from Oregon and Wyoming through California and New Mexico and found only one that was slightly bigger. This drought began in 1575, a decade after the founding of St. Augustine, Florida, and before the Pilgrims landed at Plymouth Rock in 1620.

Hot weather can be linked to drought which dries up the landscape. Normally, some of the sun’s heat evaporates moisture from the soil, but scientists say western soil is so dry that the energy instead makes the air even hotter.

“When the ground is wet, heat waves aren’t that bad,” said Williams, who calculated that the soil in the western half of the country is the driest since 1895. “But if it’s dry, we are subjected to extreme conditions risk. ”


Scientists say the forest fires that have broken out in recent days have been fueled by excessive heat in the region. Climate change contributes to drought conditions and makes trees and shrubs more likely to catch fire.

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At least 14 new wildfires have broken out this week in Montana and Wyoming as record heat has triggered an early start to the fire season. Firefighters also battled fires in Arizona and New Mexico.

“From a fire potential perspective, what is capable this year is certainly much more serious than what we have seen in the past,” said Gina Palma, fire meteorologist for the US Department of the United States on Thursday. ‘Agriculture.

Palma said drought-related fire risks are particularly pronounced at higher elevations across much of the western United States, the Rocky Mountains in the southwest, and parts of California.

“You will see very extreme fire behavior, certainly conditions that we wouldn’t normally see in June,” she said.


A growing number of scientific studies are concluding that heat waves in some cases can be directly attributed to climate change, said Kristie L. Ebi, professor at the Center for Health and the Global Environment at the University of Washington.

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This means the western United States and the rest of the world can expect more extreme heatwaves in the future, unless authorities decide to reduce greenhouse gas emissions, according to Ebi and other scientists.

A study last month estimated the percentage and number of heat deaths each year that can be attributed to man-made climate change. It included around 200 US cities and found more than 1,100 heat deaths per year from climate change, which is about 35% of all heat deaths in the country.

On average each year, Phoenix has 23 climate-induced heat deaths, Los Angeles has 21 and Tucson has 13, according to the study.

“Climate change is hurting us now,” Ebi said. “It’s a future problem, but it’s also a current problem.”


Associated Press science writer Seth Borenstein contributed from Washington. Follow Snow on Twitter at https://twitter.com/asnowreports and Borenstein at https://twitter.com/borenbears.

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