Why our annual April showers are becoming April storms

After months of cold, April brings brightness to the Northern Hemisphere. Rain helps seeds germinate, brings flower blooms, and refills drinking water supplies. But too much can hinder spring planting, lead to major flooding, and damage infrastructure.

Researchers say April showers are transforming from sprinkles into heavier storms as Earth’s temperature rises. Since the 1950s, heavier rain events have become more frequent and intense across most of the United States, according to the U.S. National Climate Assessment.

As a result, communities are dealing with more frequent and unprecedented heavy rain events. Last April, for example, heavy rains, flash flooding, tornadoes, and large hail pounded Missouri, Arkansas, Tennessee, Kentucky and Mississippi—dropping a record three months’ worth of precipitation in days. The historic round of severe weather claimed 24 lives; 15 were linked to flooding. 

Such a storm in the region is considered rare, but scientists say it was far more likely to happen today—about 40 percent more probable—than centuries ago because of human-caused climate change. And it’s only expected to worsen in the years ahead.

“What we see is that more rain is falling from heavier events and less from moderate events,” says Angeline Pendergrass, an atmospheric scientist at Cornell University. “Those are important things that we can plan for and should plan for.”

The physics of a warmer atmosphere

It’s typical to see more rain, flooding, and high river levels during springtime, especially in April. Coming out of winter, soils can be saturated from snowfall and lead to more rainfall run-off—like a sponge that can’t hold any more water. The April showers haven’t brought May flowers yet either; most plants haven’t sprouted, so roots aren’t drawing moisture from the soil. 

(Where to find the first flowers of spring)

“A little bit of rain goes a long way in the spring” says Jonathan Winter, a climate scientist at Dartmouth College.

Now, springtime storms are receiving a boost from warmer air and ocean temperatures. 

 The link between warmer temperatures and rainfall is relatively straightforward, as a warmer atmosphere can “hold” more water. For every degree Fahrenheit that air temperature rises, the atmosphere can hold 4 percent more water (known as the Clausius-Clapeyron relationship). 

(How global warming is disrupting life on Earth)

While no weather is caused by climate change, the warmer conditions are creating a more water-loaded environment for storms to thrive. 

“You can think of it as a bigger bucket,” says Winter. When an intense thunderstorm or strong cold front comes through “to squeeze out the atmosphere, you have that bigger bucket to empty.”

Warmer ocean temperatures can also increase evaporation, transferring more heat and moisture to the atmosphere. During the record rainfall last April, scientists found water in the Gulf of Mexico was heated by about 2.2 degrees Fahrenheit from climate change, increasing the amount of moisture available for the storms.

(How warm oceans supercharge deadly hurricanes)

But climate change is also affecting the flow of energy in and out of the atmosphere, says Pendergrass. As water evaporates, it pulls heat from the surface and into the atmosphere. When the vapor condenses into clouds and rain, it releases that energy and transfers it back to the surface. 

The changes in flow is also speeding up and intensifying the water cycle in some parts of the U.S., researchers found. 

Where spring storms are intensifying the most

According to the National Climate Assessment, the largest increases in extreme precipitation have occurred in the eastern half of the country, where storms can pull in more moisture from the Gulf of Mexico—particularly in the Northeast and Midwest. During its heaviest storms, the Northeast has experienced about 60 percent more rain than six decades ago, the report shows. The Midwest has seen an increase of about 45 percent more rain in their strongest downpours.

While autumn showed the largest increase in rainfall since 1950 (10 percent) largely due to tropical storms, spring and summer showed the second largest (3.5 percent). Most of the heightened spring rainfall is concentrated over the central U.S. because of more frequent intense and longer-lasting large thunderstorms, according to research. The collision of warm, moist air from the Gulf of Mexico, dry air from the Rocky Mountains, and cool, dry air from Canada causes extreme atmospheric instability and high wind shear that sustain storms for hours in the central U.S.

And research shows the extreme rains are expected to worsen, especially in the spring and Midwest. The U.S. has warmed about 2.6 degrees Fahrenheit since 1970, leading to longer heatwaves, more frequent wildfires in the West, and accelerated sea level rise. Under more warming, parts of Tennessee and Alabama, for instance, could experience 40 percent more rain in their wettest storms.

Predicting the next heavy rain

The fatal April 2025 storms across the Midwest were relatively rare, even in a warmer world—expected to occur in today’s climate about once every 90 to 240 years, analysis found. But such uncommon storms and flooding seem to be popping up more often.

(What causes flash floods? Here's how they get so destructive so quickly)

Yet Pendergrass says it’s difficult for experts to predict where a catastrophic rain event or flash flood may happen in any given year. Climate change can boost existing weather systems, but rain events are subject to many varying factors beyond temperature—like El Niño/La Niña conditions characterized by unusual ocean surface temperatures in the tropical Pacific.

“It's pretty hard to say what's going to happen…definitely should not expect to have everything monotonically increasing just a little bit different than last year,” says Pendergrass. “It's not super likely that we'll have big floods again that are a little bigger than last year in the same place.”

Even so, it is possible to anticipate the areas that will be more vulnerable to flooding during a heavy rain event. Winter says the most susceptible places are those that are low-lying, have been flooded before, close to a floodplain or has been close to flooding before. 

(What disaster preparedness experts have packed in their go bags)

“We do have extreme precipitation events that are larger than what we've seen in the historical record,” says Winter. “But in terms of the flooding damages, they're going to occur in places that previously flooded.”

In the northeast, Winter is working organizations, such as town planners and transportation departments, to better adapt to the change in rainfall extremes. Some are resizing culverts that channel water, building higher and more resilient bridges and even preemptively moving people away from flood-prone areas.

“We're not going to be surprised about who's going to get most impacted by flooding,” says Winter.