Floods, storms and hurricanes, devastating fires or heat waves… Since the beginning of the week, the United States has been hit hard by a series of disasters linked to climate change. Nearly 120 million Americans are affected by a heat wave alert that has hit parts of the Midwest and Southeast of the country. A dome of high atmospheric pressure indeed triggers exceptional phenomena on its periphery, such as record temperatures, explains the American national meteorological office. “Daytime temperatures will exceed seasonal norms by 10 to 20 degrees in many places on Friday and Saturday,” said the institute. In parts of Indiana, Kentucky and Ohio, the mercury should even reach 43°C.

“In many cases, if you have a strong enough heat wave, you will find all around its limit thunderstorms and tornadoes, flash floods, torrential rains,” American meteorologist Alex Lamers told AFP. At the northern fringe of this heat dome, high temperatures collide with masses of cool air and created severe thunderstorms on Monday, leaving several hundred thousand people without power in the Midwest. This cold front is likely to cause other destructive weather, such as hail or high winds.

Further west, Yellowstone National Park has been completely closed since Tuesday due to massive flooding and landslides that have cut roads and isolated some villages. All entrances to this 9,000 km2 park, straddling the states of Wyoming, Montana and Idaho (northwest), are affected by the closure linked to “extremely dangerous conditions” caused by rivers in flooded, swollen by rapid snowmelt and torrential rains.

According to calculations by the CNN channel, the amount of water that fell in just three days represents the equivalent of two to three months of rain for the month of June. Aerial reconnaissance revealed “major damage to multiple sections of road” linking different sites in the north of the park. “Many sections of road in this area have completely disappeared and will require significant time and effort to be rebuilt,” said the national parks agency in its latest report. “It is likely that sections in North Yellowstone will not reopen this season.”

Heatwave alerts have also been issued in several regions of California and Arizona, where temperatures and a historic chronic drought further increase the risk of fire. For several weeks, firefighters have been struggling to contain the flames of the Black Fire and Hermits Peak, which are fueled by exceptionally dry vegetation. The two fires, which have each covered more than 120,000 hectares, continued to burn in the state of New Mexico on Tuesday.

Already in 2020 and 2021, the western United States and Canada had been ravaged by flames. Last year, more than 2.5 million acres burned in California alone, in part due to the Dixie Fire, the second-largest blaze on record in the state. The latter had ravaged Greenville, a small town of 800 inhabitants, bending lampposts in the heat and destroying several historic buildings. While these phenomena are not new to the region, firefighters note that the frequency, size and intensity of forest and brush fires have continued to increase in recent years.

“Given the current state of the vegetation and the fires, I fear that we have four, five or even six very difficult months ahead of us, explains the fire chief of the Californian county of Orange, Brian Fennessy, to the Los Angeles Times. “It’s climate change. I’m no scientist, but I’ve been doing this for over 40 years, and I’ve never seen fire spread like it does. I’ve never seen what we’re going through today.”