Why flash floods are surging across the US this summer and how climate change is driving the deluge

Over the past month, record-breaking downpours have struck from Texas to New York.

Once a season of leisure, summer in the United States is now more likely to be defined by climate anxiety and destruction. In 2025, extreme flash floods have become the latest symbol of this shift — inundating cities, destroying homes, and killing hundreds. The dramatic increase in deadly deluges across multiple states isn’t a coincidence, scientists say, but a direct result of a warming climate reshaping our weather systems, CNN reported.

Over the past month, record-breaking downpours have struck from Texas to New York. A flash flood on July 4 in Texas killed more than 130 people. In the days that followed, floods ravaged Ruidoso, New Mexico; Chicago; central North Carolina; New York City; and Kansas City. These are not once-in-a-decade disasters. Some were 100- or even 1,000-year events — the kind statistically expected once every century or millennium in a stable climate. Yet now they’re happening almost weekly.

What’s driving this extreme rainfall?

According to climate experts, the underlying physics are straightforward: warmer air holds more water. And when that water gets released, it can come down with devastating intensity. “This is almost a textbook example of climate change impacts,” said climate scientist Kate Marvel. “Warm water drives more evaporation. Warm air holds more water vapor. And when it rains, it pours.”

This summer, much of the US east of the Rockies has seen unusually high levels of atmospheric moisture, thanks to warm waters in the Gulf of Mexico and the western Atlantic. As storm systems sweep across the region, they act like sponges being wrung out — dropping intense rainfall in short bursts, often over small areas.

Daniel Swain, a climate researcher at UCLA, noted that these conditions have created record-high levels of “precipitable water,” the amount of rain that would fall if all the water in the air suddenly condensed.

In short: the atmosphere is supercharged, and each passing storm is loaded with more fuel than before.

A changing weather system

Beyond the moisture, the behaviour of weather systems is also changing. Michael Mann, a climate scientist at the University of Pennsylvania, points to a phenomenon called “atmospheric resonance” — a kind of feedback in the upper atmosphere that can cause jet streams to lock into place. When that happens, weather patterns can stagnate for days or even weeks, allowing storms to linger and intensify over the same regions.

Mann and his colleagues have found that such patterns have tripled in frequency since the mid-20th century, especially during summer. These long-lived systems — sometimes not well captured in climate models — can trap moisture-rich air masses over the same location, compounding rainfall and increasing the risk of catastrophic flooding.

The most extreme events are the clearest signal

While overall annual rainfall may not change dramatically, Swain said, the most extreme events are becoming more intense — and more clearly tied to human-caused climate change. “It truly is mathematically correct that the more extreme the rain event, the clearer the connection to climate change is,” he explained.

The tragic flooding in 2025 mirrors what scientists saw coming in 2024, when an unprecedented number of flood emergencies unfolded across the US That year, too, was punctuated by summer storms dumping massive amounts of water on unprepared infrastructure and communities. “It was a warning of what was to come,” one researcher noted.

How this unfolds on the ground

The impacts of these intensified rain events depend on geography and infrastructure. Urban areas with poor drainage — like New York City’s subway system — are quickly overwhelmed. Wildfire burn scars, like those in New Mexico, become flash flood zones when even modest rainfall hits. In flatter regions, water lingers and spreads, inundating roads and homes. Poorer communities, especially those with limited access to early warning systems or flood protections, often suffer the most.

As the world warms, the risk of compounding disasters rises — not just from rain, but from the intersections of heat, drought, wildfire, and flood. A hot summer day used to mean beach outings and ice cream. Now, increasingly, it means red alerts, sirens, and clean-up crews.

“There is absolutely no doubt,” said Marvel, “that climate change, caused by human emissions of greenhouse gases, is making extreme rainfall more extreme.”