In August, 2005, Anand Irimpen, a cardiologist and a professor at Tulane University, evacuated New Orleans during the approach of Hurricane Katrina. He and his family watched it make landfall from a hotel room in Dallas. “The storm passed by and I was ready to go home,” Irimpen told me. “But then my wife said, ‘The levees broke. We can’t go back.’ ” The damage to New Orleans lingered; they ended up staying in Dallas for months. And when his hospital finally reopened, in February of the following year, doctors began noticing unexpected changes. “My fellows said they were seeing more heart attacks than before the storm,” Irimpen recalled.

At first, he thought they must be exaggerating. “You can’t just say that,” he told them. “You have to do a study.” So his team collected data on heart attacks for two years and compared it to pre-Katrina data. “I was blown away,” he said. The rate of heart attacks at his hospital was three times what it had been before the storm, a finding that made the Times-Picayune. Perhaps even more surprising is that the rate has remained elevated ever since. “I thought that in a year or two we’d come back to baseline,” Irimpen told me. “It hasn’t decreased at all.”

In an age of climate change, we can expect more storms like Katrina. Hurricane Melissa, a Category 5 storm that plowed through the Caribbean in late October, was as powerful as any Atlantic hurricane on record, with sustained winds of a hundred and eighty-five miles per hour and one of the lowest atmospheric pressures ever measured. It was fuelled by abnormally warm ocean temperatures.

When these storms come, we tend to think of their impacts in physical and immediate terms. Rachelle Salnave, a filmmaker in Haiti, sent me videos of a piece of the Route Nationale, the country’s main transportation artery, collapsing like a glacier into a roiling, swollen river. Western Jamaica was “just devastated,” George Hernandez Mejia, a director of a community relief organization, told me from Kingston. He sent me a video of what looked like acres of swift-moving flood waters, studded with dead trees. Black River, which is home to the only hospital in St. Elizabeth Parish, had been “utterly levelled,” he added. The death toll across the region was seventy-five, according to Hernandez Mejia.

But research increasingly shows that the aftereffects of disasters last longer, and extend to more domains of our lives, than official death tolls can capture. According to the National Oceanic and Atmospheric Administration (NOAA), the average tropical cyclone, a category that encompasses hurricanes and tropical storms, causes twenty-four deaths; most of them tend to be due to drownings or physical trauma. But, in 2021, a team led by Robbie M. Parks, an epidemiologist at Columbia, studied Medicare data from seventy million hospital visits across nearly a thousand counties affected by tropical cyclones. He told me that many of a hurricane’s health effects come from “a panoply of hazards” that are not normally associated with storms. In the counties studied, admissions for cardiovascular disease, infections, and injuries went up; in the week after a storm, respiratory disease spiked more than anything else. Even hospitalizations for cancer and dementia became more common.

Parks’s team estimated that, among Medicare patients alone, tropical cyclones are associated with nearly seventeen thousand excess hospitalizations per decade in the United States. “It’s shocking, to be honest,” Parks told me. He sees each hurricane as a profound disruption to affected communities. “Once the water subsides, it becomes a huge, invisible burden,” he said. The hazards extend beyond rain, flooding, or wind. “They’re existential,” he said. “They pull at every element of the fabric of society.”

A decade ago, two researchers, Edward Rappaport and B. Wayne Blanchard, set out to measure what they called the indirect deaths from storms: “Casualties that, while not directly attributable to one of the physical forces of a tropical cyclone, would not be expected in the absence of the storm.” How many more people are harmed than the official tallies suggest? “To answer those questions, one is faced with others,” the researchers wrote in a 2016 paper. How far in advance of a storm should they search? (During evacuations, a person could die from an untreated emergency or a car crash.) How long after? (Injuries can cause death weeks after they occur.) How far from the storm’s center? Where, and when, and in what way, should they look?

Rappaport and Blanchard settled on an old-fashioned methodology: scouring reams of death records in the vicinity of fifty-nine storms, dating back to 1963. (To look back at Hurricane Camille, in 1969, they reviewed more than a thousand death-certificate records.) The pair ultimately identified more than fourteen hundred indirect deaths—almost as many as the total number of direct deaths reported from the storms. Many fatalities, such as electrocutions from downed power lines, were accidental. But the largest share reflected Irimpen’s findings from New Orleans. “Heart attacks and other cardiovascular failures are the most pervasive elements in indirect deaths,” the researchers wrote. Most seemed to be triggered by physical exertion—loading sandbags before Hurricane Wilma, for example, or bailing water out of a car owing to Hurricane Floyd. But, during Hurricane Hugo, in 1989, one man reportedly dropped dead after he “saw everything he had, totally demolished.” Their research echoed findings from other studies of disasters. Three years after a 2004 earthquake in Japan, mortality from heart attacks was found to be fourteen per cent higher than pre-quake. In the two weeks after Hurricane Sandy, New Jersey recorded thirty-six more strokes and a hundred and twenty-five more heart attacks than usual. Many were fatal.

Elena Naumova, a data scientist at Tufts, was part of a team that analyzed around four hundred thousand Medicare hospitalizations after Katrina. They found that hospitalizations for cardiovascular problems increased up to sixfold, and remained elevated for two months. “These are hidden consequences,” Naumova told me. “It’s very hard to connect what happens months later to the hurricane . . . but the risks linger for a long time.” Naumova now thinks of a storm as similar to an outbreak whose effects ripple out in her data. “The health-care system will be constantly bombarded by these cascading effects,” she said. “You see one wave, and another, and another.”

When researchers want to study the collateral consequences of a major event, whether a natural disaster or a pandemic, they often use the concept of excess deaths. Mortality rates don’t capture the full extent of harm; for one thing, they exclude injuries and illnesses that people recover from. But they can capture broad trends that might otherwise escape notice. When Hurricane Maria devastated Puerto Rico, in 2017, the official death toll was sixty-four—a number that seemed low, given the storm’s violence. Then a team of researchers surveyed more than three thousand households, searching for fatalities that could be related to Maria. Based on their results, they estimated that mortality had likely increased more than sixty per cent in the three months after the storm. If all of Puerto Rico experienced a similar uptick, the storm would be responsible for nearly five thousand excess deaths.

Rachel Young, an environmental economist at the University of California, Berkeley, told me that she had read the Hurricane Maria paper and had an idea: perhaps she’d find a signal if she studied mortality across the entire United States. Young and Solomon Hsiang, a colleague at Stanford, tried to link state-by-state mortality data to five hundred tropical cyclones since 1930. “I ran the analysis, and I thought I must be doing something wrong,” she told me. “We were stunned.” Their results, published last year in Nature, suggested that the average tropical cyclone generated between seven and eleven thousand excess deaths, up to fifteen years after the storm—three hundred times as many as NOAA had tallied. For years, they tried repeatedly to invalidate their findings. “We really wanted to stress-test the result,” Young told me. In the end, they concluded that large storms “reverberate for so much longer than we thought,” she said. “They’re not just disasters of the week.”

One of the most striking findings in Young and Hsiang’s paper hinted at how storms were causing long-term damage. Infants were impacted more than any other group—and many died at least twenty-one months after the storm in question, meaning that they had not been conceived at the time of landfall. This suggested that “cascades of indirect effects,” not “personal direct exposure,” were proving deadly, Young and Hsiang wrote. Displaced people may lose access to medical care, child care, and support networks; disasters undermine not only physical but also mental health.

Irimpen’s research at Tulane helps pick apart these cascades. In his initial study, two years post-Katrina, he observed increased unemployment, lack of insurance, smoking, and substance abuse—but not an increase in risk factors traditionally associated with cardiovascular disease, such as diabetes or high blood pressure. Ten years later, however, these illnesses had increased as well. “We think there is a compounding effect,” he explained. Stress and adverse behaviors contribute to chronic diseases, which then further increase the risk of heart attacks. The disaster’s impacts were lasting enough that some of these trends took a decade to detect.

Economic factors are probably involved, too. A global 2014 study showed that national incomes decline after a cyclone and remain depressed for up to twenty years. The largest storms reduce per-capita income more than seven per cent, effectively undoing years of development. A similar study, focussed on the Philippines, found that the economic impacts of a cyclone increased infant mortality far more than the cyclone did directly. In the aftermath of the event, individuals and governments alike presumably have less to spend on resources that support health. “A hurricane destroys a road, and you have to rebuild the road,” Young said. “That money comes from somewhere; it’s a massive redistribution.” Even within a household, she said, “If you have to spend money to rebuild, that’s money you can’t spend on food.”

The rippling effects of storms are already visible in the wake of ones like Melissa. Salnave told me about a conversation she’d had with the director of Haiti’s Saint-Michel Hospital, in Jacmel. “He wondered how fuel trucks will reach the city,” she wrote. “Without fuel, the hospital’s generators can’t power the oxygen tanks or maintain electricity for patients.” Detours in the roads were difficult and dangerous, she added, and could double the time required for people to access care, if they could do so at all. Hernandez Mejia, the relief worker in Jamaica, said that roads there were inundated with thick mud, and people were walking miles in search of food and water. Tourism was an important part of the economy, he added. “Now that’s all gone,” he said. “There is a worry for those cascading effects economically.”

In a warming world, these problems will get worse. Climate change, Parks noted, causes “stronger, more powerful, and longer-lasting tropical cyclones, supercharged by forming over warmer water.” These storms will likely “magnify impacts on health and mortality.”

What we’re learning about the profound aftereffects of storms should reshape our approach to recovery and rebuilding, Young said. “Now that we know there’s this delayed impact, it should really change the amount that we invest,” she told me. Given the vulnerability of infants, she pointed out, neonatal and maternal care deserve particular assistance. She also suggested other wide-ranging interventions: small-business loans, rapid-response recovery checks, open enrollment for health-insurance plans. I pointed out that the Trump Administration may soon move in the opposite direction; earlier this year, the President said that he planned to phase out the Federal Emergency Management Agency, which responds to hurricanes. “Under all Administrations we were probably underspending on these kinds of disasters,” Young said. “We should be spending more to help people recover.” ♦