A brutal and long-lasting heatwave is threatening to wreak havoc across California this week, as sweltering conditions, power shutoffs and a severe uptick in wildfire risks coincide with 4th of July celebrations.
The dangerous weather event is expected to stretch for days with little reprieve. Starting Wednesday, parts of the state will be subject to “extreme” levels of heat risk – reaching the highest level on the National Weather Service’s index – that will last until Sunday or longer. In some areas, life-threatening triple-digit temperatures could linger for longer than a week.
“This is going to be a severe, prolonged, potentially record-breaking heatwave that may have large impacts for much of California,” said climate scientist Dr Daniel Swain during a broadcast discussion of the heat event on Monday. The long duration will only add to the potential impacts and intensity, especially because little relief can be expected even after the sun sets. “It just isn’t going to cool off – even at night,” he said.
While central and northern California are expected to bear the brunt of this event, areas in the southern part of the state are also going to cook. Heavily populated centers and rural agricultural enclaves alike could see record-setting highs during the day as well as record overnight temperatures. In the Central Valley, the state’s agricultural hub, temperatures are expected to hover near 110F through the week without dropping below 70F.
Forecasters have warned the dangerous weather conditions will pose health risks to the majority of the population, especially those unable to access cooling. “These are places where, yes, it is hot in summer – but it’s not often hot like this, and certainly not for this duration,” Swain said.
The extreme weather will also set the stage for new wildfire ignitions that can quickly turn into infernos. An abundantly wet winter left landscapes across California coated in grasses that quickly dried as the weather warmed. The yellowing hillsides and valleys are thick with fuel for fast-burning brush fires. Even deserts, typically-barren this time of year, are now primed to burn. “Unfortunately, I am not using the term ‘if wildfires develop’ because I think it’s inevitable during this event,” Swain said.
Fire risks always rise on the 4th of July, when hot dry weather aligns with explosive celebrations. Across the country, more than 18,500 fires ignite on average due to Independence Day celebrations, whether from errant fireworks or badly tended campfires. But as the temperatures rise, so do the dangers. Both fire activity and fire behavior this week will likely be extreme and new ignitions may become difficult to contain.
“It’s going to be a challenge both day and night – so the message is prevention,” said the Cal Fire deputy director Nick Schuler. The agency is at peak staffing levels to prepare for what’s expected to be an extremely busy week, extending into an extremely busy summer. Already, California has seen more than 131,400 acres burn, with months left before the risks peak.
“The important takeaway is that 95% of wildfires in California are human-caused, and the majority of them are preventable,” Schuler said, noting that careless barbequing, a spark from a trailer chain hitting the road or even some well-intended brush clearing can rapidly turn disastrous during the hottest days.
But the heat won’t only amplify the fire risks and intensity this week – it will also work to dry out more vegetation that could help fuel future fires.
A fiery start to July only adds to what’s been an incredibly hot spring. May wrapped up the 12th consecutive month of record warmth across the world. The trend continued in June in many places, including parts of California, and the summer is on track to be a scorcher. 2023 was declared the hottest year on record, and 2024 may quickly claim the title.
“Heat sucks the moisture out of vegetation and soil,” said Dr Alexander Gershunov, a research meteorologist with the Scripps Institution of Oceanography, noting that, while this may be the worst heatwave to hit California this year, it will be far from the last.
While individual weather events can be difficult to connect to global heating more broadly, “heatwaves are the most directly impacted” by the climate crisis, Gershunov explained. Fueled by human-caused warming, heatwaves are increasing in both intensity and frequency, but they are also lasting longer and covering wider areas than before. This has only added to their potential to affect human health and put strain on systems.
“Heatwaves are certainly the weather extremes that are impacted by the steroids of climate change,” he said, explaining that the effect is similar to an athlete taking performance-enhancing drugs.
Summer weather has been extreme before, but it’s going to get hotter.
“The trend is toward more frequent, more extreme, longer-lasting heatwaves all over the world,” he said. “California is certainly no exception.”
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