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California braces for ‘brutal’ floods and mudslides, but experts warn rains won’t stop historic drought

(CNN) — Parts of California, plagued by years of drought, face a threat of powerful storms at the start of the new year, bringing torrential rains and even mud and debris flows to the state.

The last of the series of storms is expected to hit the coast this Wednesday morning, and while the entire state will be impacted by the end of Thursday, it is likely that northern California and the San Francisco experience the worst of the phenomenon.

The “bomb cyclone” over the Pacific Ocean—named for how quickly it intensifies in a short period of time—causes a series of storm fronts on the West Coast. These fronts are being fed with tropical moisture from a powerful atmospheric river that extends west to Hawaii.

While the prolonged wet conditions will provide some relief from the dry conditions, the rain has turned out to be a lot in a short period of time.

According to the National Weather Service, the storm could cause more widespread flooding, highway collapse, hillside collapse, downed trees, major power outages, “immediate disruption of business, and worst of all, likely loss of life.”

“It is truly brutal what we are seeing and it must be taken seriously,” added the NWS Bay Area office.

The storms are called “atmospheric rivers” because they essentially function as a conveyor belt of concentrated moisture in the atmosphere emerging from the warm waters of the Pacific Ocean. Such a storm unleashed rain, deadly flooding, debris flows and hurricane-force winds, particularly in Northern California, including the Bay Area, over the weekend.

San Francisco prepares for brutal rains and landslides (Credit: Justin Sullivan/Getty Images)

San Francisco prepares for brutal rains and landslides (Credit: Justin Sullivan/Getty Images)

It’s all happening against the backdrop of a years-long climate change-caused mega-drought that has drained the state’s reservoirs and led to water shortages. Against that backdrop, the current storms mark the arrival of much-needed rain and snow in the state. But Daniel Swain, a climate scientist at the University of California, Los Angeles, said they won’t be enough to erase the decades-long deficit that has caused the unrelenting drought.

“This will really help a lot with Northern California’s short-term drought, maybe even erase those short-term drought conditions, but it’s going to take a lot more to fully overcome the long-term, multi-year drought impacts.” “. Swain said, emphasizing that Wednesday’s atmospheric event will be a “high-impact storm.”

These drastic shifts between periods of dryness and high rainfall, or weather whiplash, can occur more frequently and become more intense in a rapidly rising climate. Scientists say the chances of these sudden transitions happening in California will be much higher as long as humans continue to pump out planet-warming gases.

“The two faces of the same coin”

Climate researchers say the drought in the west of the country has moved into historic territory due to a mix between a lack of precipitation, higher temperatures and an increase in evaporative demand, also known as the “thirst of the atmosphere”.

As wells dry up and reservoirs empty, Julie Kalansky, a climatologist at the Scripps Institution of Oceanography in San Diego, said these storms are dramatically needed more than ever to alleviate drought, despite the dangers they bring in some areas.

“They’re two sides of the same coin: they can be extremely beneficial because they contribute a lot of California’s water supply or they can even end drought,” Kalansky told CNN. “But when they’re spread out over time, they get too strong and the landscape doesn’t have a chance to absorb all the rain, they can cause these floods.”

An aerial view of flooded areas this Sunday after heavy rains caused a levee to burst, inundating Sacramento County roads and properties near Wilton, California.

An aerial view of flooded areas this Sunday after heavy rains caused a levee to burst, inundating Sacramento County roads and properties near Wilton, California.
Fred Greaves/Reuters

This winter is already showing some signs of respite for a state that is still almost entirely in drought conditions. Large reservoirs in Northern California, including Lake Shasta and Lake Oroville, are slowly replenishing. Meanwhile, smaller reservoirs like the Folsom Dam saw a rise of roughly 40-plus feet of water in three days.

Swain said the storms will have greatly improved northern California’s dry conditions in the near term. But in the long term, he said climate change is already making its mark, and it would take much more than one exceptionally wet year — it will take several consecutive wet years and cooler conditions to end this drought.

“In a warmer climate, the severity of droughts in places like the Southwest and California is being driven by increasing evaporative demand,” he said. “Essentially, the atmosphere requires more water as temperatures rise, so you would actually need more precipitation than you used to to balance that out, and right now we’re not experiencing more precipitation than we used to in the past. ”.

Persistent drought with periods of excessive rainfall

An average atmospheric river carries more than 20 times the water that the Mississippi River carries, but in the form of steam. California is prone to flooding from these storms as they reach the Pacific Ocean, and there has already been extensive flooding from this. However, climate change is complicating the scenario, increasing the territory and the number of people —millions— that could be affected.

Rainfall in parts of California exceeded 20 centimeters over the weekend, when the latest storm tore through the state. Oakland had its wettest day on December 31 when 12 cm of rain fell, and San Francisco marked its second-wettest day with 14 cm, almost half its average rainfall for the month of December.

A 2022 study authored by Swain found that climate change has already doubled the chances of a disastrous megaflood in California in the next four decades, a storm unlike anything anyone alive has ever experienced.

And while the recent series of storms are not yet as big as they could be, the study paints a picture of what the state could face as a result of global warming.

“We haven’t seen mega-floods, but there are definitely signs of increasingly extreme precipitation even in the midst of a period characterized by fairly severe and persistent drought,” Swain said.

However, despite this wet start to the year, it is worth noting that last year was relatively much wetter around this time, and yet the state was mired in a drought for the remainder of 2022.

“The shapes of droughts are changing,” Swain said. “It’s getting easier to get into a drought, even after a very wet winter, with just that increasing evaporative demand and hotter summers.”

“Multi-year droughts will look different than they used to,” he said.

CNN’s Brandon Miller contributed to this report.

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