Why has deadly flash flooding intensified in the U.S. this summer?

Yahoo

3 days ago

If it seems like summer 2025 has been filled with reports of flooding across the U.S. — that would be accurate. The National Weather Service has issued more flood warnings this year compared with any other year on record since 1986, meteorologist Michael Lowry said in a post on X.
Through July 15, there have been 3,045 flood warnings that have been issued so far in 2025, according to data from Iowa State University. That eclipses the 3,033 warnings issued in all of 1998.
This month alone has seen several back-to-back record-breaking flooding events across the country, including the states of Texas, North Carolina, Illinois and New Mexico and across the Northeast — many of which have been deadly.
In Kansas City, Kan., on Wednesday, rain fell at a rate of 1 to 2 inches per hour, leaving drivers stranded on roads and flooding at least one family's home.
Flash floods are the most dangerous type of flooding because of how fast and powerful they are, as indicated by the National Oceanic and Atmospheric Administration.
Here are some factors to consider around the recent flash flooding events and why they seem to be getting worse.
How common are flash floods and when do they happen?
Flash floods are common during the summer when warmer air is capable of holding more moisture, versus cooler air, AccuWeather reports. More moisture in the air means more fuel for thunderstorms and rainfall.
Flash floods happen when heavy rainfall is faster than the ground's ability to absorb it, as defined by NOAA.
Two key factors contribute to flash flooding, according to the National Weather Service: the rate of rainfall and how long the rain lasts. It also depends on how well the soil can absorb the rainfall, whether there's vegetation that can help with runoff and the topography of an area.
Flash flooding can be hard to predict, which is why it can be so destructive. Flash floods 'can happen within minutes of the causative rainfall, limiting the time available to warn and protect the public,' NOAA says.
Why have flash floods escalated recently?
Population
James Booth, professor of climate change and weather at the City College of New York, told Time that one factor as to why flash floods have gotten so bad is that more people in the population means more exposure to flash floods.
'For the most part, there's more people in more places across America than there were 50 years ago. So the increase in exposure [to flash floods]—that's not a tricky physics problem,' Booth told Time. 'I think we can't discount the possibility that there were flood type events back in 1950 that didn't get recorded because they didn't affect anyone.'
Infrastructure
Water runoff happens when the ground is so saturated that it cannot absorb any more rainfall and starts to flow over the ground surface. Densely populated areas are at high risk for flash floods because buildings, highways, parking lots and driveways reduce the amount of rainfall that's absorbed into the ground. Water is then sent to storm drains that can quickly overflow or become jammed with debris.
Much of the infrastructure across the nation, including roads, sewers and drainage systems, also wasn't designed to withstand the intense rainfall events that are becoming more commonplace, AccuWeather reports.
What factors contributed to the recent flash flooding events?
Texas
In central Texas, slow-moving thunderstorms dumped an entire summer's worth of rain — more than 7 inches — over a span of hours on July 4, causing river banks to surge, resulting in flash floods that killed at least 130 people.
North Carolina
Over the July Fourth weekend, heavy rains from Tropical Storm Chantal inundated central North Carolina, killing at least six people in widespread flooding. The Eno River crested at over 25 feet, shattering a record set in 1996 by Hurricane Fran.
Illinois
On July 8, a 1-in-1,000-year rainfall event hit Chicago as 5 inches of rain fell in just 90 minutes over Garfield Park. This quickly inundated homes and low-lying streets.
New Mexico
At least three people died as a result of severe flash flooding that swept through a south-central New Mexico resort town on July 8.
Last year, the South Fork and Salt fires scorched vast areas of land, creating what's known as 'burn scars.' Without vegetation the town has been left susceptible to mudslides and increased water runoff. The heavy monsoonal rains that fell on these areas created conditions that caused water to rise rapidly, the village said.
Northeast
At least two people died due to flash flooding in Plainfield, N.J., after parts of the Northeastern U.S. and mid-Atlantic were inundated with heavy rain on July 14. The storm caused flash flooding in areas of New York, New Jersey, Pennsylvania and central Virginia that gushed through subway stations, stranded vehicles and prompted a state of emergency.
'Five of the most intense rainstorms in New York City's history have taken place in the last four years,' Department of Environmental Protection Commissioner Rohit Aggarwala said on July 15, a day after the city's subways were inundated with flash flooding.
'[New York City's] sewers were designed over the last 100 or 200 years to deal with an intense rainstorm of up to 1.75 inches per hour,' Aggarwala said. 'The pipes were designed for a certain amount of water. A lot more water fell from the sky and was trying to get into them.'
Experts say climate change is escalating flash flooding
Experts say that while flash flooding is a common summertime threat, the risks are also changing as climate change can affect how intense and frequent rainfall occurs, according to the Environmental Protection Agency.
'A warming atmosphere means more moisture availability to storms,' Marshall Shepherd, a University of Georgia meteorology professor who previously served as president of the American Meteorological Society, wrote in Forbes.
Based on the laws of thermodynamics, for every degree Celsius that rises in Earth's temperature, the atmosphere can hold about 7% more water vapor.
'Water temperatures are warmer in the Gulf and other water bodies, which also boosts available moisture for these summer storms,' Shepherd writes. 'Heavy rain has increased in every part of the U.S. over the past few decades.'
Hourly rainfall rates are 15% higher in 126 U.S. cities (out of 144 analyzed) compared to rates in 1970, as noted in a recent study from Climate Central, a nonprofit research group.
'Yes, rain storms happen naturally, but they are more 'juiced' now,' writes Shepherd.