A person looks at damage to the main building at Camp Mystic, along the banks of the Guadalupe River in Texas. A flash flood swept through the area in the early hours of July 4, 2025. Climate change is making heavy rain more common, leading to more flood risk in much of the U.S.

Julio Cortez/AP

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Julio Cortez/AP

The catastrophic flash floods in Texas over the weekend were caused by extremely heavy rain. Up to 12 inches of rain fell in South Central Texas in the early hours of July 4th, according to National Weather Service radar estimates.

Climate change is driving more extreme rain storms across much of the U.S., which drop more water in shorter periods of time and make dangerous floods more likely.

That’s what happened in Texas last week. When a large amount of rain falls very quickly, the ground can’t soak up the water. If the terrain is even a little bit hilly, all that excess water is funneled into low areas, picking up speed as it flows downstream. This can cause dangerous flash floods, when water rises quickly and is moving swiftly.

The part of Texas that flooded last week is known as Flash Flood Alley because of its impermeable limestone hills and frequent downpours, but these floods were unusually severe for the area.

And climate change is making such floods even worse.

That’s because a warmer atmosphere can hold more moisture. That extra water vapor means storms can drop more rain than in the past. Today, the heaviest rainstorms in Texas drop about 20% more water than they did in the late 1950s, when the planet was significantly cooler, according to the National Climate Assessment. And extreme rain in Texas is expected to get much more frequent in the coming decade, as the climate warms even more, according to a 2024 report by the Texas state climatologist.

It’s not just Texas. Across the U.S., the heaviest storms are projected to drop more rain as the planet continues to warm.

We don’t know yet how much climate change contributed to this particular storm. An initial analysis by a group of European scientists estimates that climate change may have caused slightly more rain to fall during the July 4 storm. Scientists will be able to do more accurate analyses as more detailed data from Texas become available in the coming days and weeks.

Friday’s rain was particularly intense because the remnants of Tropical Storm Barry were moving over Texas after the storm made landfall last week in Mexico. As the Earth warms, tropical storms and hurricanes are dumping more rain than they used to. Most of the excess heat that humans have trapped on Earth has been soaked up by the oceans, and warmer ocean water combined with warmer air in the atmosphere makes large, wet storms more likely.

Such storms can cause deadly flooding very far inland, a phenomenon that was on full display last year when Hurricane Helene caused devastating flooding in Appalachia. In 2021, flash floods from the remnants of Hurricane Ida killed dozens of people in the Northeastern U.S., after making landfall in Louisiana.

More than one third of the estimated $230 billion of damage caused by inland flooding in the U.S. between 1988 and 2021 would not have happened without human-caused climate change, according to the National Climate Assessment.

Outdated rain data hampers predictions and preparations

The flash floods in South Central Texas washed out roads and bridges, and swept away buildings and RVs along the Guadalupe River.

Despite the growing risks, many communities around the country are still not planning for more intense rainstorms as they build roads, floodways and storm infrastructure. That’s in part because local governments around the country rely on historical rainfall records from the National Oceanic and Atmospheric Administration, NOAA, to plan flood control systems. But in some places, the records are decades old, meaning they don’t reflect how rainstorms have already gotten more intense in most of the country.

In Texas’s Harris County, which includes Houston, NOAA updated the rainfall records in 2018 and found that extreme storms – those that have a 1% chance of occurring in any given year – now drop almost 18 inches of rain, compared to 13 inches prior to the 1960s and 70s.

That increase meant that one-third of the major roads and highways in Harris County are vulnerable to flooding. To respond to the growing risk, the county’s flood infrastructure plan became $150 million to $200 million more expensive, largely due to the flood safety needs.

NOAA is currently updating outdated rainfall records nationwide, taking into account how climate change could continue to make storms worse. Those updates are expected to be released starting next year.

NOAA did not respond to questions about whether that timeline is changing under the Trump administration, which has proposed significantly shrinking the agency, including programs that work on climate change research.