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RNZ News
3 days ago
- 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
3 days ago
- 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
3 days ago
- 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.
Scientific American
15-07-2025
- Climate
- Scientific American
AI Couldn't Forecast the Texas Floods
CLIMATEWIRE | Artificial intelligence is showing promise when it comes to weather forecasting, but it still couldn't predict the Texas floods. The best-performing weather models during the July 4 floods were traditional ones specially designed to produce local forecasts at high resolution. Global-scale models were far less accurate — and so were AI models, weather experts say. 'All those new fancy AI models? They missed it too,' said Daniel Swain, a climate scientist at the California Institute for Water Resources, in a live YouTube talk on July 7. On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. Some meteorologists say that could change. AI weather models are starting to exhibit an ability for deep learning of atmospheric physics, which means they could be capable of forecasting unprecedented weather events based on atmospheric conditions. New AI models are "certainly capable of predicting 'out-of-sample' events — events that they haven't seen before,' said Corey Potvin, a scientist at NOAA's National Severe Storms Laboratory in Norman, Oklahoma. But looming budget cuts at NOAA — along with years of lagging federal investment in AI weather systems — are a major hurdle for the improvement of federal AI weather models, experts say. It's the latest example of how President Donald Trump's efforts to shrink government could hobble the country's weather forecasting capabilities, at a time when extreme weather is on the rise. Kim Doster, NOAA's director of communications, said in an email that budget cuts would not negatively impact the agency's research and forecasting priorities. Commerce Secretary Howard Lutnick, head of the department that houses NOAA, "is committed to integrating advanced technologies like AI to deliver the fastest, most accurate data to Americans," she said. "This administration is working hand-in-hand with meteorologists and scientists to modernize research, cut forecast lead times, improve mapping, and streamline operations across the bureau." Today's most advanced AI weather prediction models largely exist in the private sector. Many of them failed to see the Texas floods coming with the same accuracy as the high-resolution traditional forecasts. One major reason is that many AI models are still focused on forecasting large-scale weather patterns at the global level, according to Russ Schumacher, a meteorologist at Colorado State University and Colorado's state climatologist. 'Forecasting precipitation at the local scale is very challenging, and has not really been the focus of most of the AI models in use now,' he said in an email. That's despite some recent suggestions that the Texas forecasts could have benefited from more investment in AI prediction at the National Weather Service. Tim Gallaudet, who served as acting NOAA administrator during the first Trump administration, suggested in a July 7 op-ed that NWS should 'incorporate more artificial intelligence' into its atmospheric, oceanic and hydrologic modeling systems for more accurate forecasts during incidents like the Texas floods. But some scientists have expressed concerns about AI's ability to forecast record-breaking weather events, like the extreme rainfall that triggered the Texas floods. AI systems are often trained on historical weather data, and extreme events are — by definition — rare. That means there aren't many examples of them for AI systems to learn from. In a 2023 comment published in the scientific journal Nature, weather experts Imme Ebert-Uphoff and Kyle Hilburn warned that AI systems are 'often unpredictable when the program operates under conditions that it has never encountered before,' adding that extreme weather events 'might therefore trigger highly erratic predictions.' Potvin predicted new AI models could forecast rare events, though not quite as accurately as they would if they had lots of examples to train on. And although most AI models are still focused on large-scale weather patterns, high-resolution models are likely on the horizon. NOAA is working on some local weather-modeling projects that include AI components. The National Severe Storms Laboratory's experimental Warn-on Forecast system, or WoFS, is designed to rapidly incorporate radar and satellite observations into a high-resolution model. It can produce updated forecasts about every 15 minutes, increasing meteorologists' ability to accurately warn communities about sudden extreme events, like flash floods. NSSL scientists are also perfecting an AI version of WoFS, known as WoFSCast. By design, it can only perform as well as the original non-AI model — but it can theoretically produce forecasts much faster and with far less computing power, making it a cheaper option for local NWS offices. There's also NOAA's High-Resolution Rapid Refresh model, known for its ability to forecast storms at the local scale. HRRR was one of the models that best predicted the rainfall in Texas — and scientists are developing an AI version as well, a model known as HRRRCast. 'As far as I know, WoFSCastand HRRRCast are the only [AI] models currently being developed for higher resolution prediction,' Potvin said. Lag in investment NOAA still lags far behind the private sector when it comes to investment in AI weather prediction. That's a big concern for NWS forecasts, some experts say. AI is swiftly becoming a new frontier in weather modeling, and it could easily become an asset to NWS meteorologists — if NOAA had more resources to invest. 'The private sector is well ahead of where NOAA is now, to the point that even if we were in normal budget cycles, I'm not sure they could catch up,' Mary Glackin, former president of the American Meteorological Society, said at an AMS-hosted panel last week. Meanwhile, the White House has proposed around $2.2 billion in cuts to NOAA in its budget request for fiscal year 2026. Chief among these is the elimination of NOAA's entire research arm. That includes the agency's large network of cooperative research institutes and laboratories, like the NSSL, where researchers are still improving forecasting systems like WoFS and its AI counterpart. Scientists have warned that these cuts would damage NOAA's weather forecasting capabilities, putting communities at risk when extreme weather events strike. The private sector alone can't make up for lagging federal investments in weather forecasting technology, scientists and meteorologists have warned. Agencies like NWS are invested in public service and free forecasts, with the aim of ensuring that all U.S. communities — even those with limited resources — have access to high-quality, life-saving weather warnings. More public-private partnerships could help NOAA get a jump on AI weather system development, Glackin suggested. Such an arrangement 'meets the needs of the private sector, who are looking for a profit and a competitive edge, but remains true to the public service concept and not leaving the least behind,' she said. But such partnerships require the continued existence of research infrastructure at NOAA — which might not survive if Congress follows through with Trump's proposed cuts. Meanwhile, AI isn't the only frontier in weather forecasting. Traditional weather models also improve year over year as scientists collect and incorporate more data. That's how hurricane forecasts become so advanced over the last few decades. "As big a fan as I am of AI, it would be a mistake to put all of our investment into AI and then neglect the traditional side of weather modeling,' Potvin said. 'Because that in the end, would be undercutting future AI development.' Meteorologists have warned that traditional weather forecasts will plateau — or even degrade — if Trump's proposed cuts go into effect and hamstring NOAA's research capabilities. 'I worry about the loss of investments in science,' Brad Colman, another former AMS president, said at the July 10 panel. 'That's our seed corn, and the impact of that will be long-lasting. So I really hope that a greater wisdom will prevail, and that we will maintain that capacity.'
