Californien:Tørke, rekordvarme, brande og nu måske oversvømmelser

Californiere forsøgte at klare ekstremerne af et skiftende klima fredag, da en straffende hedebølge, der har hjulpet med at brænde dødelige skovbrande, fik staten til at vippe på kanten af ​​strømafbrydelser for en 10. dag i træk, mens en tropisk storm løb i land med løftet om køligere temperaturer, men også mulig oversvømmelse.

Det bratte sving i forholdene piskede endda vejrjunkier.

"Dette er måske den mest usædvanlige og ekstreme vejruge i et stykke tid i Californien - og det siger noget. Puha," skrev Daniel Swain, en klimaforsker ved University of California, Los Angeles, på sin blog om det vestlige vejr.

Selvom regnen kan være velkommen i den tørkeplagede tilstand og vil bringe lindring med mere normale temperaturer, forventes syndfloder og mere brutale hedebølger at blive faste inventar, efterhånden som klimaændringer opvarmer planeten og vejrrelaterede katastrofer bliver mere ekstreme.

"Vi vil se, at disse hedebølger fortsætter med at blive varmere og varmere, længere og længere, mere skovbrande," sagde Jonathan Overpeck, dekan ved University of Michigan School for Environment and Sustainability. "Odserne for virkelig intens nedbør stiger. Og det er derfor, vi er bekymrede for oversvømmelser forbundet med denne resterende orkan."

Californien er blot det seneste offer i et år med til tider dødelige hedebølger, der begyndte i Pakistan og Indien i foråret og fejede ind over dele af den nordlige halvkugle, inklusive Kina, Europa og andre områder i USA.

Klimaændringer har også forværret tørke, udtørret floder, gjort skovbrande mere intense og – omvendt – ført til massive oversvømmelser rundt om på kloden, da fugt, der fordamper fra land og vand, holdes i atmosfæren og derefter genaflejres af intens regn.

Forskere er tilbageholdende med at tilskrive nogen specifik vejrbegivenhed, såsom orkanen Kay, der nu er nedgraderet til en tropisk storm, når den er på vej ind i Californien, til global opvarmning. Men de siger, at hedebølger er præcis den type forandring, der vil blive mere almindelig.

Den såkaldte varmekuppel, der kogte Californien, blev sat på plads af et usædvanligt højtryksområde over Grønland, af alle steder, som i det væsentlige skabte en meteorologisk trafikprop, sagde Paul Ullrich, professor i regional klimamodellering ved University of California, Davis. Det forhindrede højtrykssystemet, der tvang varm luft over Californien i at bevæge sig med.

Et telt uden for et tidligere teater i LA's Chinatown sagde:"Satan ringede. Han vil have sit vejr tilbage."

Temperaturerne nåede et rekordhøjt niveau i Sacramento på 116 grader (46,7 C) tirsdag. Mange andre steder slog rekorder for september og endnu flere satte daglige topkarakterer.

Varmen, der farvede vejrkortene mørkerøde i mere end en uge i Californien, er kun et eksempel på kommende attraktioner.

Sacramento, statens hovedstad, har omkring 10 "ekstrem varme" dage om året, og det vil fordobles igen ved midten af ​​århundredet. I 1970'erne havde byen fem, sagde Ullrich.

"That's pretty much going to be the story for much of the Central Valley and much of Southern California," Ullrich said. "This kind of exponential growth in the number of extreme heat days. If you tie those all together, then you end up with heat waves like we've experienced."

For nine days through Thursday, the vast energy network that includes power plants, solar farms and a web of transmission lines strained under record-setting demand driven by air conditioners.

"If we're going to build a statue to anybody in the West, it will be a Willis Carrier," said Bill Patzert, retired climatologist at NASA's Jet Propulsion Laboratory, about the inventor of the air conditioner. "Really large areas of Southern California would essentially be unlivable without air conditioning."

Air conditioning puts the biggest strain on power sources during a heat wave and operators of the electrical grid called for conservation and warned of the threat of power outages as usage hit an all-time high Tuesday, surpassing a record set in 2006.

The state may have averted a repeat of rolling outages two summers ago by sending a first-ever text alert that blared on 27 million phones urging Californians to "take action" and turn off nonessential power. Enough turned up thermostats, turned off lights or pulled the plug on appliances to avoid power cuts, though thousands of customers did lose power at various times for other reasons.

The West is in the throes of a 23-year megadrought that has nearly drained reservoirs and put water supplies in jeopardy. That, in turn, led to a sharp decrease in hydropower that California relies on when power is in peak demand.

"Part of the country that's getting hit worst is the Southwest and Western United States," Overpeck said. "It is a global poster child for the climate crisis. And this year, this summer, it's really the Northern Hemisphere has been just an unusually hot and wildfire-plagued hemisphere."

The extreme heat helped fuel deadly wildfires at both ends of the state as flames fed on grass, brush and timber already "preconditioned to burn" by drought and then pushed over the edge by the heatwave, Overpeck said.

Firefighters struggled to control major wildfires in Southern California and the Sierra Nevada that exploded in growth, forced thousands to evacuate and produced smoke that could interfere with solar power and further hamper electricity supplies.

Two people were killed in the fire that erupted last Friday in the Northern California community of Weed at the base of Mount Shasta. Two others died trying to flee in their car from a fire in Riverside County that was threatening 18,000 homes.

What remains of the hurricane is expected to bring heavy rains and even flash floods to Southern California from Friday night through Saturday. Strong winds could initially make it difficult and dangerous for firefighters trying to corral blazes, Patzert said.

Heavy downpours could also unleash mudslides on mountainsides charred by recent fires. While several inches of rain could fall, much of it will run off the arid landscape and will not make a dent in the drought.

"It comes at you like a firehose and you're trying to fill your champagne glass," Patzert said. "Everybody's sort of excited, but on Saturday night a lot of people will be saying, 'Yeah, we could have done without that.'" + Udforsk yderligere

Two dead, thousands told to flee California wildfire

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