El Niño occurs when surface waters warm across the central and eastern tropical Pacific, weakening or even reversing the trade winds that typically blow from the Americas toward Asia. That shift sends warm water sliding eastward, fueling rising air and storm activity. Historically, the pattern has meant wetter winters for Southern California, and this year’s version is shaping up to be an intense one.

“Big El Niño events tend to tilt the odds toward more winter storms hitting the North Pacific, and bigger storms too, because of the energy the ocean pumps into the atmosphere,” said Dan Cayan, a researcher at the Scripps Institution of Oceanography.

Scientists classify an El Niño when sea surface temperatures rise half a degree Celsius above normal, according to Tyler Rodenbaugh, chief meteorologist for the San Diego County Water Authority. When temperatures climb 1.5 degrees above normal, forecasters call it a “very strong” El Niño — which is exactly what’s developing now.

Past strong El Niño winters have brought San Diego prolonged, heavy rain. During 1982-83, the region logged 70 rainy days, compared with the usual 40 to 45 — roughly one and a half times the normal number of storm days, Cayan said. The same pattern repeated in 1997-98. Both winters dumped nearly 20 inches of rain at Lindbergh Field, far above the typical 10-inch average, and also boosted Sierra Nevada snowpack, driving heavier statewide runoff.

But the so-called “Godzilla El Niño” of 2015-16 broke that trend, delivering a relatively dry winter with just 8 inches of rain recorded at the airport.

“What actually happens depends on specific storms called atmospheric rivers, which aren’t governed by El Niño itself,” said Alexander Gershunov, a research meteorologist at Scripps. Atmospheric rivers are long, narrow bands of moisture-rich air — essentially rivers in the sky — that can unleash torrential rain regardless of the broader ocean pattern.

Built at the base of hillsides, atop flood plains and threaded with canyons, San Diego’s geography makes it especially vulnerable to flooding. How much damage actually occurs often comes down to the condition of the infrastructure meant to hold the water back.

The devastating January 2024 flooding along Chollas Creek, which damaged roughly 1,000 homes in the Shelltown neighborhood, remains a stark example. Fire officials have described it as a once-in-a-thousand-year event that was largely unavoidable, with Cayan noting the creek drains a small watershed vulnerable to sudden, intense downpours.

But many residents argue the damage was worsened by years of neglected maintenance. Thousands of flood survivors have filed lawsuits claiming the city failed to properly maintain its storm drain channels, and many say they continue to suffer health problems — including skin rashes, respiratory issues and swelling — that they attribute to floodwater exposure or the mold that later took hold in their homes.

The city’s current budget cites more than $800 million already spent on stormwater system upgrades, including 18 completed projects last year, but also lists $3.3 billion in additional needed improvements without a clear funding plan. City officials say crews are working to keep the drainage system as functional as possible, clearing channels and debris so water can flow freely during storms. Fire-Rescue Deputy Chief Robert Rezende, who is overseeing the city’s El Niño preparedness effort, said crews are also coordinating with the San Diego Lifeguard Service’s swift-water rescue team to clear brush, open floodgates and remove obstructions to ensure emergency access if people become trapped.

San Diego County is taking similar steps, monitoring conditions and dispatching field crews to clean storm drains and culverts, trim trees and sweep roads in unincorporated areas, according to county spokesperson Donna Durckel.

In North County, Rep. Mike Levin announced a $26 million federal grant to repair the levee system along the San Luis Rey River near Oceanside and clear sediment from the channel — improvements to a flood-prone waterway that had been promised since 1970 but never carried out.

Pollution remains another persistent concern. Residents of southern San Diego and neighboring Imperial Beach regularly contend with sewage and industrial runoff flowing north from the Tijuana River. During heavy rain, that flow can overwhelm treatment plants, sending more untreated waste into the river and out to the ocean, creating hazardous beach conditions.

Flood control efforts are further complicated by the age of San Diego’s dams, which average about 100 years old — among the oldest in the nation. Four dams have safety issues requiring repair, including one at Lake Hodges rated “unsatisfactory” with an “extremely high downstream hazard potential” by the state Division of Safety of Dams.

That dam needs full replacement, but a plan to rebuild it by 2029 collapsed after cost estimates jumped from $275 million to as much as $697 million. The county water authority had agreed to cover half the replacement cost but backed out once the price more than doubled.

City officials are pressing forward regardless. In 2024, the City Council approved a 10-year, $100 million management contract for San Diego’s Dam Safety Program and expanded its dam safety team, which handles inspections and maintenance. The city is currently designing 36 short-term repair projects, according to spokesperson Jennifer McBride, though officials estimate $3 billion will be needed over the coming decades to complete all necessary upgrades.

In the meantime, the state has ordered San Diego to keep Lake Hodges below 280 feet to reduce the risk of dam failure during flooding. Some residents worry the lower water level is harming wildlife habitat, while reduced water storage could also raise wildfire risk — a real concern given that El Niño winters can swing toward drought just as easily as deluge.

Then there’s the surf. Big waves are already on forecasters’ radar, delighting surfers while worrying coastal officials. These swells build as sea levels rise from warmer water expansion, low-pressure systems, shifting ocean circulation patterns, and the layering of higher sea levels atop unusually high tides.

Gershunov warned that oversized waves can devastate coastal infrastructure, pointing to the 1982-83 El Niño, when the historic Scripps Pier suffered irreparable damage and the landmark Marine Room restaurant flooded. “There was a lot of coastal damage because big waves coincided with astronomically high tides,” he said. “The risk of coastal damage and erosion is elevated again this winter.”

Still, he noted a silver lining: “I think surfers who love big waves should be pretty happy this winter.”

Original source: CalMatters

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The climate pattern, driven by warmer-than-normal waters in the tropical Pacific and weakened trade winds, has historically ushered in wet winters for Southern California. But its track record is inconsistent enough that emergency planners are hedging their bets rather than betting on a single outcome.

“Large El Niños tend to tilt the odds toward more winter storms moving through the north Pacific, and bigger ones too, because of the extra energy the ocean feeds into the atmosphere,” said Dan Cayan, a climate researcher at Scripps Institution of Oceanography.

Still, the relationship between ocean warming and actual rainfall has grown less reliable in recent decades, complicating forecasts and pushing local governments to prepare for a broad spectrum of possibilities. Compounding the uncertainty is San Diego’s stormwater infrastructure, much of it decades old, along with a fleet of century-old dams that need major repairs.

In response, the city of San Diego has assembled an El Niño task force pulling in representatives from every municipal department to coordinate emergency response.

“From San Ysidro up through Sorrento Valley and Lake Hodges — anywhere there’s a creek, river or lake — we have to watch those spots closely to make sure we’re ready if extreme weather hits,” said Assistant Fire Chief Robert Rezende, who is overseeing the effort.

A pattern with a mixed history

El Niño takes shape when sea surface temperatures rise in the central and eastern tropical Pacific. The trade winds that typically blow from the Americas toward Asia slacken, sometimes even reversing course toward the California coast. That shift pushes warm water eastward, causing air to rise and spawning storm activity.

Meteorologists classify an El Niño once ocean temperatures climb a half-degree Celsius above average, according to Tyler Rodenbaugh, senior meteorologist for the San Diego County Water Authority. A reading of 1.5 degrees above normal earns the label “very strong” — which is where conditions stand today.

History shows these events can bring dramatically more rain. During the El Niño winters of 1982-83 and 1997-98, San Diego logged about 70 rainy days compared with the usual 40 to 45, and nearly 20 inches of rain fell at Lindbergh Field, roughly double a typical year’s total. Statewide, Sierra Nevada snowpack swelled as well, adding to runoff.

Yet the so-called “Godzilla El Niño” of 2015-16 broke that pattern entirely, delivering just 8 inches of rain at Lindbergh Field — well below normal.

“What actually happens depends on individual storms known as atmospheric rivers, and those don’t necessarily follow El Niño’s lead,” said Alexander Gershunov, a research meteorologist at Scripps.

Atmospheric rivers are narrow bands of concentrated moisture — essentially rivers flowing through the sky — that ferry water vapor from the tropics and can trigger intense downpours, according to the National Oceanic and Atmospheric Administration.

Flood risk on the ground

San Diego’s terrain — hillside developments, floodplain construction and a maze of canyons — makes it especially prone to flooding when storms do arrive. How much damage results often comes down to whether the region’s flood-control systems can keep pace.

The January 2024 flooding along Chollas Creek offered a stark example, damaging roughly 1,000 homes in the Shelltown neighborhood of southeastern San Diego.

Rezende described it as a “1,000-year flood” that couldn’t have been avoided, and Cayan noted the creek’s small watershed is especially vulnerable to sudden, intense rain bursts. But many residents believe the destruction was made worse by years of deferred maintenance. Thousands filed lawsuits alleging the city failed to properly maintain its storm channels, worsening the flooding. Survivors say they continue to grapple with health issues — rashes, respiratory trouble, swelling — that they link to floodwater exposure and subsequent mold contamination in their homes.

The city’s current budget touts more than $800 million already spent on stormwater upgrades, including 18 projects finished last year, but acknowledges another $3.3 billion in needed work without a clear funding plan. City officials did not respond to requests from CalMatters for additional details on stormwater spending.

Still, officials say they’re keeping up routine maintenance where they can. The Stormwater Department is clearing debris from channels to keep water flowing during storms, according to Rezende, and is coordinating with the San Diego Lifeguard Service’s swiftwater rescue team to clear vegetation, open gates and remove obstructions so rescuers can reach anyone trapped by rising water.

San Diego County is taking similar precautions, tracking weather forecasts and sending crews to clear drains and inlets, trim trees and sweep streets in unincorporated areas, county spokesperson Donna Durckel said.

Further north, Rep. Mike Levin recently secured a $26 million federal grant to repair the levee system protecting the San Luis Rey River near Oceanside and to clear sediment buildup from the channel — repairs residents had been promised since 1970 but never received.

Pollution remains a persistent headache as well. Communities in south San Diego and neighboring Imperial Beach regularly deal with sewage and industrial contamination flowing from the Tijuana River. Heavy rain can overwhelm treatment plant capacity, sending more untreated waste downstream and fouling coastal waters.

Aging dams add to the risk

San Diego’s flood-control challenges are compounded by dams that average 100 years old, among the oldest in the country. Four are flagged for safety concerns requiring repair, including the dam at Lake Hodges, which state regulators rate “unsatisfactory” with “extremely high downstream hazard potential,” according to the California Division of Safety of Dams.

That dam needs to be rebuilt entirely, but a plan to complete the project by 2029 collapsed after cost estimates jumped from $275 million to as much as $697 million. The San Diego County Water Authority, which had agreed to split the cost, pulled out once the price more than doubled.

The city is now moving forward on its own. In 2024, the City Council approved a 10-year, $100 million contract to manage its Dam Safety Program, expanding the team responsible for inspections and maintenance and drawing up 36 near-term repair projects, according to city spokesperson Jennifer McBride. Full upgrades across the system are expected to cost $3 billion over the coming decades.

In the meantime, the state has directed the city to keep Lake Hodges below 280 feet to reduce the chance of dam failure during a major storm. Some residents argue the lower water level is hurting wildlife habitat and could leave the area more vulnerable during wildfire season — a real concern given that El Niño years can just as easily bring drought as deluge.

Waves to watch

Beyond flooding, forecasters are also eyeing dramatic surf conditions this winter — a mixed blessing for surfers and coastal managers alike.

Rising sea levels driven by warmer water expansion, shifting atmospheric pressure systems and altered ocean currents can combine with unusually high “king tides” to produce punishing swells.

Such waves have caused serious damage before. During the 1982-83 El Niño, massive surf destroyed the historic Scripps Pier beyond repair and flooded the landmark Marine Room restaurant. “There was a lot of coastal damage because the big waves coincided with astronomically high tides,” Gershunov said. “The risk of coastal damage and erosion is higher again this winter.”

Still, he noted a silver lining: “I think the surfers who love big waves should be satisfied this winter.”

Original source: CalMatters

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“I’ve never seen so many people homeless as what I have right now,” said Janalea England, of Steinhatchee, Florida, a small river town along the state’s rural Big Bend, as she turned her commercial fish market into a storm donation site for friends and neighbors, many of whom couldn’t get insurance on their homes.

Helene blew ashore in Florida’s Big Bend region as a Category 4 hurricane late Thursday with winds of 140 mph (225 kph).

From there, it quickly moved through Georgia, where Gov. Brian Kemp said Saturday that it “looks like a bomb went off” after viewing splintered homes and debris-covered highways from the air. Weakened, Helene then soaked the Carolinas and Tennessee with torrential rains, sending creeks and rivers over their banks and straining dams.

Western North Carolina was isolated because of landslides and flooding that forced the closure of Interstate 40 and other roads. All those closures delayed the start of the East Tennessee State University football game against The Citadel because the Buccaneers’ drive to Charleston, South Carolina, took 16 hours.

There have been hundreds of water rescues, none more dramatic than in rural Unicoi County in East Tennessee, where dozens of patients and staff were plucked by helicopter from a hospital rooftop Friday. And the rescues continued into the following day in Buncombe County, North Carolina, where part of Asheville was under water.

“To say this caught us off guard would be an understatement,” said Quentin Miller, the county sheriff.

Asheville resident Mario Moraga said it’s “heartbreaking” to see the damage in the Biltmore Village neighborhood and neighbors have been going house to house to check on each other and offer support.“There’s no cell service here. There’s no electricity,” he said.

While there have been deaths in the county, Emergency Services Director Van Taylor Jones said he wasn’t ready to report specifics, partially because downed cell towers hindered efforts to contact next of kin.

Relatives put out desperate pleas for help on Facebook. Among those waiting for news was Francine Cavanaugh, whose sister told her she was going to check on guests at a vacation cabin as the storm began hitting Asheville. Cavanaugh, who lives in Atlanta, hasn’t been able to reach her since then.

“I think that people are just completely stuck,” she said.

The storm, now a post-tropical cyclone, was expected to hover over the Tennessee Valley on Saturday and Sunday, the National Hurricane Center said.

‘Catastrophic’ flooding

It unleashed the worst flooding in a century in North Carolina, where Gov. Roy Cooper described it as “catastrophic” as search and rescue teams from 19 states and the federal government came to help. One community, Spruce Pine, was doused with over 2 feet (0.6 meters) of rain from Tuesday through Saturday.

And in Atlanta, 11.12 inches (28.24 centimeters) of rain fell over 48 hours, the most the city has seen over two days since record keeping began in 1878.

President Joe Biden said Saturday that Helene’s devastation has been “overwhelming” and pledged to send help. He also approved a disaster declaration for North Carolina, making federal funding available for affected individuals.

With at least 25 killed in South Carolina, Helene is the deadliest tropical cyclone for the state since Hurricane Hugo killed 35 people when it came ashore just north of Charleston in 1989. Deaths also have been reported in Florida, Georgia, North Carolina and Virginia.

Moody’s Analytics said it expects $15 billion to $26 billion in property damage. AccuWeather’s preliminary estimate of the total damage and economic loss from Helene in the U.S. is between $95 billion and $110 billion.

Climate change has exacerbated conditions that allow such storms to thrive, rapidly intensifying in warming waters and turning into powerful cyclones sometimes in a matter of hours.

The storm, now a post-tropical cyclone, was expected to hover over the Tennessee Valley on Saturday and Sunday, the National Hurricane Center said.

Evacuations and overtopped dams

Evacuations began before the storm hit and continued as lakes overtopped dams, including one in North Carolina that forms a lake featured in the movie “Dirty Dancing.” Helicopters were used to rescue some people from flooded homes.

And in Newport, Tennessee, Jonah Wark waited so long to evacuate that a boat had to come to the rescue. “Definitely a scary moment,” Wark said.

After touring the damage by helicopter, a stunned U.S. Rep. Diana Harshbarger said, “Who would have thought a hurricane would do this much damage in East Tennessee?”

Among the 11 confirmed deaths in Florida were nine people who drowned in their homes in a mandatory evacuation area on the Gulf Coast in Pinellas County, where St. Petersburg is located, Sheriff Bob Gualtieri said.

None of the victims were from Taylor County, which is where the storm made landfall. It came ashore near the mouth of the Aucilla River, about 20 miles (30 kilometers) northwest of where Hurricane Idalia hit last year at nearly the same ferocity.

“If you had told me there was going to be 15 feet to 18 feet of storm surge, even with the best efforts, I would have assumed we would have had multiple fatalities,” Florida Gov. Ron DeSantis said Saturday.

Taylor County is in Florida’s Big Bend, went years without taking a direct hit from a hurricane. But after Idalia and two other storms in a little over a year, the area is beginning to feel like a hurricane superhighway.

“It’s bringing everybody to reality about what this is now with disasters,” said John Berg, 76, a resident of Steinhatchee, a small fishing town and weekend getaway.

Timmy Futch of Horseshoe Beach stayed put for the hurricane before driving to high ground when the water reached his house. many homes in the town, which his grandfather helped found, were reduced to piles of lumber.

“We watched our town get tore to pieces,” Futch said.

The storm, now a post-tropical cyclone, was expected to hover over the Tennessee Valley on Saturday and Sunday, the National Hurricane Center said.

The aftermath

A Florida resident provided a devastating first-hand look at hard-hit Cedar Key Friday morning after parts of the town were flattened by Hurricane Helene.

About 60 miles (100 kilometers) to the north, cars lined up before sunrise Saturday at a free food distribution site in Perry, Florida, amid widespread power outages.

“We’re making it one day at a time,” said Sierra Land, who lost everything in her fridge, as she arrived at the site with her 5- and 10-year-old sons and her grandmother.

Thousands of utility crew workers descended upon Florida in advance of the hurricane, and by Saturday power was restored to more than 1.9 million homes and businesses. But hundreds of thousands remain without electricity there and in Georgia.

Chris Stallings, director of the Georgia Emergency Management and Homeland Security Agency, said crews were focused on opening routes to hospitals and making sure supplies can be delivered to damaged communities.

Helene was the eighth named storm of the Atlantic hurricane season, which began June 1. The National Oceanic and Atmospheric Administration has predicted an above-average season this year because of record-warm ocean temperatures.

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By Columbia Mailman School of Public Health

The Southwest and West face a second week of extreme temperatures that have already claimed more than a dozen lives. Approximately one in three Americans received excessive heat warnings, watches or advisories last weekend, according to the National Weather Service. Globally, July was the hottest month on record, pushing the world closer to the critical 1.5-degree Celsius temperature rise threshold, the most optimistic target for limiting global warming.

Meanwhile, Canadian wildfires, preceded by doubts, continue to create smoke that carries thousands of miles, triggering air quality warmings and unhealthy conditions across wide swaths of the United States, reaching as far south as Miami, and communities across New England and the Northeast struggled to recover from recent powerful storms and flash flooding.

Environmental health scientists from Columbia University Mailman School of Public Health—home to the country’s first climate and health program in a school of public health—are working to study and address these challenges, both through original research and teaching front-line health workers and the next generation of public health leaders.

“There is no doubt that extreme weather and wildfires are happening with greater frequency because of climate change,” says Cecilia Sorensen, an emergency medicine physician and associate professor of environmental health sciences at Columbia Mailman School. Studies show that climate change has led to a 50 percent increase in the acreage burned. “We are especially concerned with vulnerable groups, including individuals with preexisting respiratory and cardiovascular conditions, the elderly, small children, and infants, people without stable housing, and those who work outside.”

Sorensen points to a slate of health risks from extreme weather. Exposure to wildfire smoke is dangerous for people with asthma and other respiratory conditions and prolonged time spent outdoors is a risk to everyone. High temperatures are most dangerous to the same vulnerable groups, including the elderly and those who work and live outside. Stormy weather introduces the risk of injury, such as from landslides and downed powerlines, and creates a breeding ground for mosquitoes and other infectious disease vectors. All these stressors disrupt lives and have a negative impact on mental health—as can the larger anxiety about climate change.

In situations of extreme weather, individuals should seek out guidance from their local authorities on cooling centers, road closures, masking guidance, and more. Air quality information is available online(link is external and opens in a new window) and offers a general framework for how safe it is to be outdoors. Sorensen adds her own advice: “Check in on your loved ones. Often our most valuable front-line responders are friends and family,” she says.

Sorensen leads the Global Consortium on Climate and Health Education (GCCHE), which is based at Columbia Mailman. With 310 medical, nursing, public health, and other health professions schools as members, GCCHE develops curricula and conducts trainings on climate and health around the world. She is a member of the Lancet Countdown on Health and Climate Change(link is external and opens in a new window) and serves on the National Academy of Medicine Action Collaborative for Decarbonization of the U.S. Health Sector(link is external and opens in a new window). She is the co-editor of the textbook Climate Change and Human Health: From Science to Practice.

In its trainings, GCCHE focuses on ways communities can protect themselves and build resiliency. These include early warning systems for extreme weather, rain gardens and other methods to mitigate flooding, cooling centers, and more.

Informing these trainings is research by Sorensen and other Columbia Mailman faculty scientists, including Darby Jack, Marianthi-Anna Kioumourtzoglou, Robbie Parks, Jeff Shaman, Lew Ziska, and others. These studies have linked elevated temperatures to injury deaths(link is external and opens in a new window), wildfire smoke to jump in ICU admissions(link is external and opens in a new window), tropical cyclones to elevated hospitalizations(link is external and opens in a new window) and death rates, including the specific illnesses involved(link is external and opens in a new window) and special risks to older adults(link is external and opens in a new window). They have also examined the effects of heat stress on kidney function of agricultural workers(link is external and opens in a new window), as well as the broader impacts of climate change on women’s health(link is external and opens in a new window) and on food security. Meanwhile, research continues to demonstrate the negative health impacts of the main driver of climate change—air pollution from fossil fuel combustion.

“Climate changing is stressing all of society, especially the most vulnerable,” says Sorensen. “It’s critical that we come together to protect ourselves as extreme weather becomes the new normal. At the same time, we need to push for a speedy transition to a green economy.”

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