Latest news with #DanielSwain
E&E News
5 days ago
- Climate
- E&E News
‘Biggest, baddest' rainfall events are getting worse
Texas hill country. Central North Carolina. New Mexico. Chicago. Kansas City. New York. Flash floods have wreaked havoc across the country this summer, transcending geography, topography and the built environment from the rural Southwest to the largest cities in the Midwest and Northeast. The outcomes have been fueled, in each case, by slightly different factors. Hard concrete surfaces in Chicago and New York forced rainwater to pool in the streets or pour into the subways. Wildfire scars near Ruidoso, New Mexico, left the soil loose and vulnerable to floods. Hilly terrain in Kerr County, Texas, sent runoff cascading into the nearby Guadalupe River, which swiftly overflowed its banks. Advertisement But a common ingredient triggered them all: explosions of torrential — and in some cases, record-breaking — rainfall. These heavy precipitation events are among the clearest symptoms of climate change, scientists say. Copious studies warn that they're already happening more often and becoming more intense, and they'll continue to worsen as global temperatures rise. And the most catastrophic rainfall events may be worsening the fastest, some experts say. 'The biggest, baddest, rarest extreme precipitation events are precisely those which are going to increase the most in a warming climate,' Daniel Swain, a climate scientist at the California Institute for Water Resources, said in a live YouTube talk shortly after the Texas floods struck in July. 'There is really abundant scientific evidence for this at this point.' Intensifying rainfall events are the product of simple physics, scientists explain. A warmer atmosphere can hold more water, increasing the odds that moisture-laden clouds will drop rainfall bombs when they burst. That rule has been well established for nearly 200 years. A 19th-century equation known as the Clausius-Clapeyron relation — still widely referenced by researchers today — dictates that air can hold about 7 percent more moisture with every degree Celsius of warming. But in recent years, scientists have noticed an alarming trend. Extreme storms in some parts of the world appear to be defying the Clausius-Clapeyron relation, producing far more rainfall as temperatures rise than the equation would predict. One recent study examined the influence of climate change on the unusually active 2020 Atlantic hurricane season. It noted that extreme short-term rainfall rates produced by the 2020 storms appear to have scaled at about twice the rate suggested by the Clausius-Clapeyron relation, given that climate change has warmed the Atlantic Ocean basin by as much as 0.9 degrees Celsius. In general, there's increasing evidence that the 'most intense convective downpours — meaning the heaviest torrential rain events from thunderstorms, specifically — are already increasing at a rate that greatly exceeds that of other types of precipitation,' Swain said. It's a phenomenon scientists have dubbed the super-Clausius-Clapeyron rate. Researchers are still investigating the reasons it's happening. At least one recent study, published in April, suggests the trend could be a statistical quirk caused by an increase in the frequency of thunderstorms compared with milder rainfall events. In other words, it's not that the storms themselves are defying established physics — the strongest kinds of storms are just becoming more common. That study focused only on storms in Europe, meaning more research is needed to understand what's happening with rainfall events around the globe. Still, the authors note that rainfall rates are clearly increasing faster than expected in some cases — and that's a trend scientists should account for when making projections for the future. At the same time, researchers have pointed to other ways climate change may be supercharging the worst precipitation events. One recent study warns that long-lasting summer weather patterns, such as extended heat waves or lingering storms, are on the rise — and physical changes in the atmosphere, driven by global warming, may be to blame. When already heavy rainfall events stall in place, they can dump massive volumes of water on a single location, triggering life-threatening floods. Put together, the science suggests that communities should prepare for record-breaking storms and flash flood events to continue worsening across the U.S., researchers warn. These events have been 'significantly underestimated as a hazard in a warming climate,' Swain said in his YouTube talk. 'There's a lot of evidence right now with the most recent science … that these are precisely the kinds of events that are going to increase the most, and in fact already are, and much faster than 'ordinary' precipitation events.'
RNZ News
21-07-2025
- Climate
- RNZ News
This is the summer of flooding across the US, and scientists know why
By Andrew Freedman , CNN A man looks at a damaged road after severe flash flooding that occurred during the July 4 holiday weekend, in Hunt, Texas, on July 6. Photo: Ronaldo Schemidt/AFP/Getty Images via CNN Newsource Once synonymous with leisure and reprieve, summer has increasingly become a season marked by anxiety and disruption. Fossil fuel pollution - alongside other compounding factors - has transformed these months into a time of mounting peril, punctuated by relentless heat waves, rampant wildfires and catastrophic flooding. This summer, in particular, has been defined by a tragic surge in deadly flash floods across the United States, underscoring the escalating volatility of our warming world. It's no accident this is the summer of flooding, climate scientists say, with 100-year to 1,000-year deluges happening nearly simultaneously in multiple states on multiple days. Large parts of the US have seen an unusually humid summer with record amounts of moisture in the air. When cold fronts and other weather systems come along, that moisture can get wrung out, squeezed like a water-laden sponge, yielding heavy and often highly localized downpours. For much of the summer, the atmospheric conditions over the US have funneled humid air north from the unusually warm Gulf and western Atlantic, including the Gulf Stream, UCLA climate researcher Daniel Swain told CNN. This has yielded unusually high levels of moisture at all levels of the atmosphere across the US east of the Rockies, Swain said. It has led to record levels of what meteorologists call precipitable water, which is the amount of rain that would result from instantaneously extracting all the water in the air. This pattern has led to one flash flood after another. Omar Gutierrez, 31, helps clear debris from the inundated dining area of La Salsa Kitchen, a Mexican restaurant, after deadly flash flooding in Ruidoso, New Mexico, July 9. Photo: Paul Ratje/Reuters via CNN Newsource First and foremost, there was the devastating Texas flood that killed more than 130 people on the night of July 4. But flash flood events have been focused elsewhere as well. Three people were killed in a flash flood related to torrential rains falling on a wildfire burn scar in Ruidoso, New Mexico, on July 8. Some major roads in Chicago were suddenly under water when a 1,000-year rainfall event struck in early July. In portions of North Carolina, the remnants of Tropical Storm Chantal led to deadly heavy rain and flooding the same weekend as the Texas tragedy . In New York City, water rushed into the subway tunnels when the city saw its second-heaviest rainfall total in one hour on July 14, with widespread flash flooding lasting into the 15th. And this past week, it was Kansas City's turn to flood on July 17. Some of these floods resulted from rainfall that has a return frequency of about 1,000 years, meaning it has just a 0.1% chance of occurring in any given year. But climate change is loading the dice in favor of extreme precipitation. "When we talk about e.g. '1000 year' events, we're talking about the likelihood of these events in the absence of human-caused warming (i.e. how often we would expect them from natural variability alone)," said climate scientist Michael Mann of the University of Pennsylvania. "These events are of course much more frequent *because* of human-caused warming," he said in an email. But his research has identified other factors, such as persistent large-scale weather patterns known as "atmospheric resonance," that can make extreme weather, including floods, even more likely. Just as sound waves or ocean waves can resonate and reinforce each other, atmospheric resonance can happen to undulating jet stream patterns in the upper atmosphere, resulting in weather systems that stay in place for weeks. A recent study Mann worked on found such weather patterns have tripled in incidence since the mid-20th century during the summer months. The problem is these patterns are "not necessarily well-captured in climate models," he said. This increases uncertainty about future projections for extreme weather trends. The influence of climate change on heavy rainfall is most evident when it comes to short duration extreme events, like what has happened repeatedly this summer, according to Swain. "It is not average precipitation that really is most affected by climate change," Swain said. "It truly is mathematically correct that the more extreme the rain event, the clearer the connection to climate change is." Tropical Storm Chantal flooded central North Carolina with torrential rain, seen here in Chapel Hill on July 7. Photo: Peter Zay/Anadolu/Getty Images via CNN Newsource The physics of how global warming affects heavy precipitation events is well known, according to climate scientist Kate Marvel. "This is almost a textbook example of climate change impacts," she told CNN. "The science behind it is so basic you can see it in daily life. Warm water drives more evaporation - the bathroom gets much steamier after a hot bath than a cold one," she said. "Warm air contains more water vapor - a cold beer gets wet on the outside on a hot day, because when air comes into contact with the cooler surface, it has to condense out its water vapor," Marvel said. "Warm ground makes it easier for moist air to balloon upwards - this is why thunderstorms happen on hot summer afternoons. Put these all together, and you get the perfect conditions for torrential rain," said Marvel, author of the new climate book "Human Nature." "Whether a downpour turns into a catastrophic flood depends on a lot of things: how porous the ground is, the topography of the area, the people and things in harm's way. But there is absolutely no doubt that climate change, caused by human emissions of greenhouse gases, is making extreme rainfall more extreme." - CNN
CNN
20-07-2025
- Climate
- CNN
This is the summer of flooding across the US, and scientists know why
Storms Climate change Air quality PollutionFacebookTweetLink Follow Once synonymous with leisure and reprieve, summer has increasingly become a season marked by anxiety and disruption. Fossil fuel pollution — alongside other compounding factors — has transformed these months into a time of mounting peril, punctuated by relentless heat waves, rampant wildfires and catastrophic flooding. This summer, in particular, has been defined by a tragic surge in deadly flash floods across the United States, underscoring the escalating volatility of our warming world. It's no accident this is the summer of flooding, climate scientists say, with 100-year to 1,000-year deluges happening nearly simultaneously in multiple states on multiple days. Large parts of the US have seen an unusually humid summer with record amounts of moisture in the air. When cold fronts and other weather systems come along, that moisture can get wrung out, like squeezing a water-laden sponge, yielding heavy and often highly localized downpours. For much of the summer, the atmospheric conditions over the US have funneled humid air north from the unusually warm Gulf and western Atlantic, including the Gulf Stream, UCLA climate researcher Daniel Swain told CNN. This has yielded unusually high levels of moisture at all levels of the atmosphere across the US east of the Rockies, Swain said. It has led to record levels of what meteorologists call precipitable water, which is the amount of rain that would result from instantaneously extracting all the water in the air. This pattern has led to one flash flood after another. First and foremost, there was the devastating Texas flood that killed more than 130 people on the night of July 4. But flash flood events have been focused elsewhere as well. Three people were killed in a flash flood related to torrential rains falling on a wildfire burn scar in Ruidoso, New Mexico, on July 8. Some major roads in Chicago were suddenly under water when a 1,000-year rainfall event struck in early July. In portions of North Carolina, the remnants of Tropical Storm Chantal led to deadly heavy rain and flooding the same weekend as the Texas tragedy. In New York City, water rushed into the subway tunnels when the city saw its second-heaviest rainfall total in one hour on July 14, with widespread flash flooding lasting into the 15th. And this past week, it was Kansas City's turn to flood on July 17. Some of these floods resulted from rainfall that has a return frequency of about 1,000 years, meaning it has just a 0.1% chance of occurring in any given year. But climate change is loading the dice in favor of extreme precipitation. 'When we talk about e.g. '1000 year' events, we're talking about the likelihood of these events in the absence of human-caused warming (i.e. how often we would expect them from natural variability alone),' said climate scientist Michael Mann of the University of Pennsylvania. 'These events are of course much more frequent *because* of human-caused warming,' he said in an email. But his research has identified other factors, such as persistent large-scale weather patterns known as 'atmospheric resonance,' that can make extreme weather, including floods, even more likely. Just as sound waves or ocean waves can resonate and reinforce each other, atmospheric resonance can happen to undulating jet stream patterns in the upper atmosphere, resulting in weather systems that stay in place for weeks. A recent study Mann worked on found such weather patterns have tripled in incidence since the mid-20th century during the summer months. The problem is these patterns are 'not necessarily well-captured in climate models,' he said. This increases uncertainty about future projections for extreme weather trends. The influence of climate change on heavy rainfall is most evident when it comes to short duration extreme events, like what has happened repeatedly this summer, according to Swain. 'It is not average precipitation that really is most affected by climate change,' Swain said. 'It truly is mathematically correct that the more extreme the rain event, the clearer the connection to climate change is.' The physics of how global warming affects heavy precipitation events is well known, according to climate scientist Kate Marvel. 'This is almost a textbook example of climate change impacts,' she told CNN. 'The science behind it is so basic you can see it in daily life. Warm water drives more evaporation — the bathroom gets much steamier after a hot bath than a cold one,' she said. 'Warm air contains more water vapor — a cold beer gets wet on the outside on a hot day, because when air comes into contact with the cooler surface, it has to condense out its water vapor,' Marvel said. 'Warm ground makes it easier for moist air to balloon upwards – this is why thunderstorms happen on hot summer afternoons. Put these all together, and you get the perfect conditions for torrential rain,' Marvel, author of the new climate book 'Human Nature,' said. 'Whether a downpour turns into a catastrophic flood depends on a lot of things: how porous the ground is, the topography of the area, the people and things in harm's way. But there is absolutely no doubt that climate change, caused by human emissions of greenhouse gases, is making extreme rainfall more extreme.'
CNN
20-07-2025
- Climate
- CNN
This is the summer of flooding across the US, and scientists know why
Storms Climate change Air quality PollutionFacebookTweetLink Follow Once synonymous with leisure and reprieve, summer has increasingly become a season marked by anxiety and disruption. Fossil fuel pollution — alongside other compounding factors — has transformed these months into a time of mounting peril, punctuated by relentless heat waves, rampant wildfires and catastrophic flooding. This summer, in particular, has been defined by a tragic surge in deadly flash floods across the United States, underscoring the escalating volatility of our warming world. It's no accident this is the summer of flooding, climate scientists say, with 100-year to 1,000-year deluges happening nearly simultaneously in multiple states on multiple days. Large parts of the US have seen an unusually humid summer with record amounts of moisture in the air. When cold fronts and other weather systems come along, that moisture can get wrung out, like squeezing a water-laden sponge, yielding heavy and often highly localized downpours. For much of the summer, the atmospheric conditions over the US have funneled humid air north from the unusually warm Gulf and western Atlantic, including the Gulf Stream, UCLA climate researcher Daniel Swain told CNN. This has yielded unusually high levels of moisture at all levels of the atmosphere across the US east of the Rockies, Swain said. It has led to record levels of what meteorologists call precipitable water, which is the amount of rain that would result from instantaneously extracting all the water in the air. This pattern has led to one flash flood after another. First and foremost, there was the devastating Texas flood that killed more than 130 people on the night of July 4. But flash flood events have been focused elsewhere as well. Three people were killed in a flash flood related to torrential rains falling on a wildfire burn scar in Ruidoso, New Mexico, on July 8. Some major roads in Chicago were suddenly under water when a 1,000-year rainfall event struck in early July. In portions of North Carolina, the remnants of Tropical Storm Chantal led to deadly heavy rain and flooding the same weekend as the Texas tragedy. In New York City, water rushed into the subway tunnels when the city saw its second-heaviest rainfall total in one hour on July 14, with widespread flash flooding lasting into the 15th. And this past week, it was Kansas City's turn to flood on July 17. Some of these floods resulted from rainfall that has a return frequency of about 1,000 years, meaning it has just a 0.1% chance of occurring in any given year. But climate change is loading the dice in favor of extreme precipitation. 'When we talk about e.g. '1000 year' events, we're talking about the likelihood of these events in the absence of human-caused warming (i.e. how often we would expect them from natural variability alone),' said climate scientist Michael Mann of the University of Pennsylvania. 'These events are of course much more frequent *because* of human-caused warming,' he said in an email. But his research has identified other factors, such as persistent large-scale weather patterns known as 'atmospheric resonance,' that can make extreme weather, including floods, even more likely. Just as sound waves or ocean waves can resonate and reinforce each other, atmospheric resonance can happen to undulating jet stream patterns in the upper atmosphere, resulting in weather systems that stay in place for weeks. A recent study Mann worked on found such weather patterns have tripled in incidence since the mid-20th century during the summer months. The problem is these patterns are 'not necessarily well-captured in climate models,' he said. This increases uncertainty about future projections for extreme weather trends. The influence of climate change on heavy rainfall is most evident when it comes to short duration extreme events, like what has happened repeatedly this summer, according to Swain. 'It is not average precipitation that really is most affected by climate change,' Swain said. 'It truly is mathematically correct that the more extreme the rain event, the clearer the connection to climate change is.' The physics of how global warming affects heavy precipitation events is well known, according to climate scientist Kate Marvel. 'This is almost a textbook example of climate change impacts,' she told CNN. 'The science behind it is so basic you can see it in daily life. Warm water drives more evaporation — the bathroom gets much steamier after a hot bath than a cold one,' she said. 'Warm air contains more water vapor — a cold beer gets wet on the outside on a hot day, because when air comes into contact with the cooler surface, it has to condense out its water vapor,' Marvel said. 'Warm ground makes it easier for moist air to balloon upwards – this is why thunderstorms happen on hot summer afternoons. Put these all together, and you get the perfect conditions for torrential rain,' Marvel, author of the new climate book 'Human Nature,' said. 'Whether a downpour turns into a catastrophic flood depends on a lot of things: how porous the ground is, the topography of the area, the people and things in harm's way. But there is absolutely no doubt that climate change, caused by human emissions of greenhouse gases, is making extreme rainfall more extreme.'
San Francisco Chronicle
16-07-2025
- Climate
- San Francisco Chronicle
This is what is keeping California cool while the rest of the U.S. sizzles
While much of the country has endured a barrage of historic floods and punishing heat and humidity this month, California's summer has been surprisingly tame. The Bay Area is already on track for one of its coolest starts to summer in decades, and forecast data suggest that trend isn't going anywhere. The Climate Prediction Center calls for continued below average temperatures across the state, essentially through the end of the month. The lingering cool trend is a result of a broader atmospheric setup that's been locked in for weeks. East of the Rocky Mountains, a sprawling and stubborn Bermuda high pressure system is pumping in heat, humidity and bouts of heavy rain. But over California, the jet stream has flattened into a fast-moving west-to-east flow of winds, interrupted only occasionally by subtle dips in the upper atmosphere. UCLA climate scientist Daniel Swain described this pattern as a ' sticky weak disturbance,' and the setup has been on repeat since early June. The airflow around a stronger than normal North Pacific High continues to stir up cooler water along the West Coast, while driving a surge of warm water across the central Pacific. This sets up a positive feedback loop; cooler coastal waters sharpen the daily temperature and pressure gradients from the ocean to the Central Valley, which enhance onshore winds and reinforce the cloud deck. The result is more marine layer influence, lower high temperatures, especially near the coast. It's not just the coast that's feeling the cooler temperatures. Inland areas that typically bake this time of year like the Central Valley, interior Bay Area and the high deserts, have struggled to mount any multiday heat waves. The kind of prolonged, widespread heat events California saw in July 2024 require a robust high pressure ridge centered closer to California, something that just hasn't materialized so far this summer. The extended 8- to 14-day temperature outlook shows a similar pattern, with continued cool conditions across California. Still, the state won't avoid the heat altogether. Brief surges into the triple digits remain likely in places like Redding, Fresno and Palm Springs. But those hot spells will be short-lived and the marine influence will remain strong along the coast. The cooler temperatures, both daytime and overnight, help tamp down fire weather risks. But as we push deeper into summer and fuels continue to dry, fire activity is still expected to increase. Wednesday's weather in the Bay Area will be a continuation of the pattern, with daytime highs running about 10 degrees below normal and marking the coolest day of the week. Wednesday outlook San Francisco: A thick marine layer will generate patches of drizzle in the early morning. And from there, the clouds will be slower to retreat to the coast than yesterday. But retreat they will, leaving a mostly sunny Wednesday afternoon and evening. Temperatures will top out in the low 60s west of the Twin Peaks and in the mid-60s downtown and in the Mission. Winds from the southwest pick up during the afternoon and clouds will return after dark, with lows in the mid-50s. North Bay: Pockets of drizzle will develop in Santa Rosa and along the Marin coast in the morning. Cloud cover from the marine layer will extend all the way back to Fairfield, but they will quickly break up by the early afternoon. Despite the sunshine, it's another cool day, with temperatures in the low to mid-70s. More clouds and drizzle overnight with lows in the 50s. East Bay: A thick cloud deck will extend all the way to I-680 in the morning. Things will clear up rather quickly across the interior and south of Oakland, with clouds hanging on a bit longer in Berkeley and Richmond. Temperatures will range from the upper 60s to low 70s in the I-580/I-80 stretch, with highs in the mid-70s to around 80 degrees in Hayward, Concord and Livermore. Mostly cloudy again overnight with lows in the mid- to upper 50s. Pacific Coast and Peninsula: Does the Pacific Coast see the sun this day? It's a tossup. Some sunshine may break through the clouds in the afternoon from Half Moon Bay up to Pacifica with temperatures in the low 60s. The rest of the Peninsula east of Skyline Boulevard will clear up earlier, with temperatures ranging from the upper 60s in South San Francisco, the low 70s in San Mateo and the mid-70s in Redwood City. The clouds return overnight with pockets of drizzle along the coast and lows in the 50s. South Bay and Santa Cruz: A predominantly southwesterly wind will keep the clouds locked and temperatures muted for a good part of the day in Santa Cruz, where it will be a struggle to hit 70 degrees. The South Bay will once again be the warm spot in the region, with temperature in the low 80s. Mostly cloudy again overnight with lows in the mid-50s.
