New research shows that hurricanes and tropical storms in the United States cause a sharp increase in deaths for almost 15 years after the storm hits.

Official government statistics only give the number of people killed in these storms, which are collectively called “tropical cyclones.” Typically, these direct deaths, which official estimates put at an average of 24 per storm, occur as a result of drowning or other types of trauma. However, a new analysis, published on October 2 in Naturereveals a larger, hidden death toll in the wake of hurricanes.

“Each month, people die earlier than they would have if the storm had not hit their community,” said study senior author Solomon Hsiang, a professor of environmental social sciences at the Stanford Doerr School of Sustainability.

“A big storm will hit and there will be cascading effects: urban rebuilding, household displacement, or social networks being severed. These cascades have serious public health consequences.”

Hsiang and lead author Rachel Young estimate that the average U.S. tropical cyclone indirectly kills between 7,000 and 11,000 additional people. Overall, they estimate that tropical storms have accounted for between 3.6 and 5.2 million U.S. deaths since 1930 — more than all deaths nationwide from car accidents, infectious diseases or battle fatalities during the same period. Official government statistics put the total death toll from these storms at around 10,000.

Underestimated effects of the hurricane

The new estimates are based on a statistical analysis of data from 501 tropical cyclones that hit the Atlantic and Gulf coasts between 1930 and 2015, as well as the mortality rates of different populations in each state immediately before and after each cyclone.

Scientists developed ideas from a 2014 Hsiang study that found tropical cyclones slow economic growth by 15 years, and a 2018 Harvard study that found Hurricane Maria caused nearly 5,000 deaths in the three months after as the storm hit Puerto Rico – almost 70 times the official government count.

“When we started, we thought we might see a delayed effect of tropical cyclones on mortality, perhaps by six months or a year, similar to heat waves,” said Young, a doctoral candidate at the University of California, Berkeley, where she began working on the study as a graduate student at Hsiang’s lab before joining the Stanford faculty in July 2024.

The results show that hurricane deaths remain significantly higher not only for months but years after flood waters recede and public attention begins.

Unequal health burdens

Young and Hsiang’s study is the first to suggest that hurricanes are an important factor in the distribution of overall mortality risk across the country. While the study found that more than three in 100 deaths nationwide are related to tropical cyclones, the burden is much greater for some groups, with black people three times more likely to die from a hurricane than white people .

This finding brings into stark relief concerns that many Black communities have stoked for years about the unequal treatment and experiences they face in the wake of natural disasters.

Scientists estimate that 25% of infant deaths and 15% of deaths among people ages 1 to 44 in the U.S. are related to tropical cyclones. Young and Hsiang write that for these groups, the additional risk from tropical cyclones makes a large difference in overall mortality risk because the group starts with a low baseline mortality rate.

“These are babies born many years after the tropical cyclone, so they couldn’t even have experienced the event in utero,” Young said. “This points to a long-term economic and maternal health situation in which mothers may not have as many resources even years after a disaster as they would in a world where they have never experienced a tropical cyclone.”

Adaptation in future danger zones

The long, slow rise in cyclone-related deaths tends to be much higher in places that have had fewer hurricanes in the past. “Because this long-term impact on mortality had never been documented before, no one in the field knew to adapt to it and no one in the medical community had planned a response,” Young said.

The study’s findings could inform government and financial decisions on climate change adaptation plans, build coastal climate resilience and improve disaster management, as tropical cyclones are expected to become more intense as the climate changes.

“As the climate changes, we expect tropical cyclones to become potentially more dangerous, more damaging, and have an impact on who they hit,” Young said.

Towards solutions

Based on Nature research, Hsiang’s Global Policy Lab at Stanford University is currently working to understand why tropical storms and hurricanes cause deaths every 15 years. This research group combines economics, data science and social science to answer policy questions that are central to managing the planet’s resources, often related to the effects of climate change.

Given the mortality risk from hurricanes, the challenge is to untangle the complex chains of events that follow a cyclone and that may ultimately impact human health and then evaluate possible interventions.

These events can be so disconnected from the initial threat that even the people affected and their families may not see the connection. For example, as Hsiang and Young write, individuals may use retirement savings to repair property damage, thereby reducing their ability to pay for future health care. Family members may move away, weakening support networks that may be crucial to good health in the future.

Public spending may focus on immediate recovery needs at the expense of investments that could otherwise promote longer-term health.

“Some solutions may be as simple as telling families and governments that a few years after allocating money for treatment, you may want to think about additional savings for health care costs, especially for older people, communities of color and mothers or mothers-to-be,” she said Young.