In brief:
- The atmosphere can contain more water vapor when it’s warmer, enabling tropical cyclones to dump more rain.
- Tropical cyclones are already dropping more rain than they did in the past.
- Studies from several different research groups have found that climate change worsened the rainfall of recent hurricanes, such as Hurricanes Harvey, Helene, and Melissa.
- Slow-moving, stalled, and slow-to-weaken tropical cyclones may also increase in frequency because of climate change.
- Dangerous freshwater flooding from tropical cyclones is likely to increase in the future.
One of the more confident predictions scientists can make for future tropical cyclones — the catch-all term for hurricanes, tropical storms, and tropical depressions — is that they will dump more rain. Global warming increases the amount of water vapor the atmosphere contains when fully saturated: Every one degree Celsius of ocean warming leads to about 7% more water vapor in saturated air.
This increase in atmospheric water vapor can cause a much larger increase in hurricane rainfall than one might think. The reason: Water vapor retains the extra heat energy required to evaporate it, and when it condenses into rain, this “latent heat” is released. The extra heat helps power the hurricane, making it larger and more intense, allowing it to pull in water vapor from an even larger area and dump even more rain.
For example, a 2024 study found that hurricanes undergoing rapid intensification — which occurs more often now because of climate change — take in approximately three times more moisture (up to 2,500 km from the cyclone center) than non-rapidly intensifying hurricanes and dump far more rainfall.
When an intense hurricane makes landfall, it carries this expanded moisture plume inland. A 2019 study found a significantly increasing heavy rain threat since 1900 from landfalling major U.S. hurricanes that are now carrying higher amounts of moisture inland because a warmer atmosphere holds more water vapor.
Observations show hurricanes are dumping heavier rains
Generally, climate change has been increasing the magnitude and frequency of extreme precipitation events in the early 21st century at a rate more quickly than previously anticipated, making the 20th-century definitions of a one-in-100-year storm seriously outdated. A one-in-100-year storm is one that has about a 1% chance of occurring in a given year.
A 2023 paper, Exposure of the US population to extreme precipitation risk has increased due to climate change, found that in the U.S., “as much as one-third of the population is expected to experience the current definition of a one-in-100-year storm as often as three times in their lifetime.” The authors provided a map of how much the odds of a one-in-100-year storm had changed in the new climate of the 21st century (Fig. 1).
Observations of rainfall from tropical cyclones in the U.S. plotted over two overlapping 50-year periods from 1949-2018 (Fig. 2) show that the area of the U.S. experiencing a four-inch (100 mm) tropical cyclone rainfall event at least once every 25 years has increased by 70%. That matters because a four-inch event is a general precipitation threshold for generating flooding. And very concerningly, rarer but far more destructive extreme rainfall events of at least eight inches (200 mm) saw a greater than 10-fold increase in area.
A 2021 paper found that globally, the rainfall rate of tropical cyclones increased by about 8% between 1999 and 2018. Most of this increase occurred in the outer spiral bands; a decrease in precipitation was noted in the inner core region. A 2021 paper, Global increase in tropical cyclone rain rate, reported a similar result. A 2023 paper attributed the observed decline in inner-core precipitation to more cooling of the ocean occurring in the cold wakes of hurricanes as the climate warms.
Keep in mind, though, that an increase in extreme precipitation does not always translate to an increase in extreme flooding. A 2015 study found that very heavy precipitation — in the 99th percentile — in the contiguous U.S. resulted in 99th-percentile flooding only 36% of the time. The odds of 99th-percentile flooding increased to 62% when the soils were already moist, though.
Near-real-time attribution studies evaluate the influence of climate change on hurricanes
Still in their infancy, attribution studies examining specific hurricanes evaluate the degree to which climate change influenced a given weather event. For example, three independent attribution studies using different methodologies estimated that climate change increased the rainfall of 2017’s Hurricane Harvey in Texas by 13%-28% and rainfall intensity by 8%-19%. The most recent Intergovernmental Panel on Climate Change (IPCC) report concluded that attribution studies had shown that “there is high confidence that human-caused climate change contributed to extreme rainfall amounts during Hurricane Harvey (2017) and other intense tropical cyclones.” A 2020 paper estimated that the economic costs of Hurricane Harvey attributable to climate change ranged from 33 to 74% of Harvey’s total damage.
Traditional attribution studies take months to years to be completed because of the intensive computer simulations needed for the work. But in recent years, near-real-time attribution studies have appeared, primarily using a “storyline” approach in which a model simulates the hurricane twice — first using the present climate, and then using a theoretical climate without climate change. This approach is typically not computationally intensive, so it can be done very quickly after an extreme event. However, it has the limitation that only the change in magnitude of an extreme weather event can be judged, not the change in probability.
Michael Wehner, a scientist at Lawrence Berkeley National Laboratory who has used the “storyline” approach to investigate how warming affected rainfall in dozens of tropical cyclones, said in a recent interview for Climate Central, “Every single hurricane we’ve looked at is wetter because of climate change.”
An example of the storyline technique is shown in Fig. 3 for a 2023 study he co-authored on Category 4 Hurricane Ian of 2022. Ian dumped 10 to 20 inches (250-500 mm) of rain across much of Florida, bringing “widespread historic freshwater flooding that caused destruction and significant damage to many structures and roadways, leading to over 250 water rescues and 12 deaths,” according to the National Hurricane Center. Wehner’s study used a model that was run both with and without the influence of climate change, determining that Ian’s extreme rainfall amounts increased by 18% because of climate change.
Scientists have performed similar event attribution analyses for Hurricanes Katrina (2005), Irma (2017), Maria (2017), Florence (2018), and Hurricane Dorian (2023), finding that human-caused climate change increased their rains by 5-10%.
Three different groups released rapid-attribution studies after 2025’s Hurricane Melissa made landfall in Jamaica as the strongest landfalling hurricane on record, with sustained winds of 185 mph (300 km/h). The Imperial College of London found that human-caused climate change increased Hurricane Melissa’s eyewall rainfall rate by 16%, and that increase, along with the 7% increase in winds attributable to climate change (11 mph, or 18 km/h), made 34% of its damages attributable to climate change. World Weather Attribution, an international scientific group, concluded that climate change was increasing the intensity of rainfall in hurricanes like Melissa by more than 9%. A third organization, France-based climatameter.org, found hurricanes similar to Hurricane Melissa are locally up to 14 mm per day (up to 10%) wetter today than in the past.
The three groups have also released reports on two devastating hurricanes that hit Florida in 2024, Helene and Milton, finding that climate change likely intensified the rains of the hurricanes by as much as 30%.
Slow-moving, stalled, and slower-decaying hurricanes may increase because of climate change
A slower-moving tropical cyclone will tend to dump more concentrated rains over small areas, representing an increased flood threat, and there is some evidence from researchers Kossin (2019) and Hall and Kossin (2019) for a slowing of tropical cyclone forward speeds over the continental U.S. and in near-coastal regions over the past century, between 1948 and 2017. The slowdown can plausibly be linked to climate change, but more research is needed to confidently make this connection (see, for example, Zhang et al. 2020).
As discussed in our previous post, dangerous high-volume extreme precipitation events are increasing over the contiguous U.S., with seven out of 11 of the top events since 1949 occurring in the past 10 years. Six of these events were slow-moving tropical systems.
In addition, if a hurricane stalls near land, it can dump more concentrated rains. A 2026 paper, Global stalled tropical cyclones in a changing climate, found that stalled tropical cyclones produce about 12% more accumulated rainfall within an area about 15% smaller than that of non-stalled storms. The study predicted that under a moderate global warming scenario, climate change will cause an increase in tropical cyclones stalling near or inland along the Atlantic coast, increasing daily rainfall by about 28% by the years 2062-2099.
Also, if hurricanes are weakening at a slower rate once they move inland, they will remain stronger longer and tend to dump more rain. A 2020 paper, Slower decay of landfalling hurricanes in a warming world, argued that such a shift may have already occurred for Atlantic hurricanes. The authors found that in the late 1960s, a typical Atlantic hurricane lost about 75% of its intensity in the first day past landfall. However, the corresponding decay in recent years had been only about 50%. Using computational simulations, they showed warmer sea surface temperatures induce a slower decay by increasing the stock of moisture that a hurricane carries as it hits land. They concluded, “our findings suggest that as the world continues to warm, the destructive power of hurricanes will extend progressively farther inland.”
What the future holds: wetter storms
Under a moderate global warming scenario, four prominent studies completed using the IPCC models found a 10-29% increase in mean end-of-century tropical cyclone rain rates within 100 kilometers of the storm center.
A 10-29% increase in rainfall rate may not seem like a big deal, but according to the U.S. Army Corps of Engineers, most coastal engineering works in the U.S. aren’t designed for such extremes. A 20% increase in extreme rainfall can often cause a threshold to be crossed, for example, when a levee designed to hold a one-in-50-year flood becomes overwhelmed by what is now a one-in-40-year flood.
Although storm surge has historically been a major killer during U.S. hurricanes, freshwater flooding has been an increasingly dangerous threat in recent years (Fig. 4), thanks to some very wet (and mostly slow-moving) storms such as Harvey (2017), Helene (2024), and Florence (2018).
Damages and deaths from freshwater flooding are only going to increase as hurricanes become wetter — and potentially slower-moving — because of climate change. A 2022 paper, Tropical cyclone climatology change greatly exacerbates US extreme rainfall-surge hazard, projected that along the majority of the U.S. coast, the most intense 10% of hurricanes would intensify by 15-30% and move 20-30% more slowly in the future compared to the historical period.
“The increase in storm intensity coupled with the decrease in translation speed drives an increased likelihood to observe both extreme rainfall and extreme storm tide in the future,” the authors wrote.
Bob Henson contributed to this post.
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