The true death toll of hurricanes in the U.S.

Tropical cyclones may have a more adverse public health impact than previously considered, particularly among young or black individuals.

Study: Mortality caused by tropical cyclones in the United States. Image Credit: BEST-BACKGROUNDS / Shutterstock.com

A recent study published in Nature investigates the excess mortality associated with tropical cyclones in the contiguous United States (CONUS) between 1930 and 2015.

The effects of tropical cyclones

Tropical cyclones, which are also referred to as hurricanes, represent a significant threat to the United States’ coasts, as they often inflict infrastructure, home, and business destruction, population displacement, societal and economic disruption, ecological changes, reduced availability of essential services, increased pollution, agricultural damage, and death.

Previous studies have primarily focused on direct mortality attributed to tropical cyclones. However, this narrow focus can may underestimate the wider costs of natural catastrophes, as they cause complex cascades of events.

About the study

In the present study, researchers estimate the mortality burden of 501 tropical cyclones throughout the CONUS coastline between 1930 and 2015. Excess deaths were calculated for every 100,000 individuals and wind speed in m/sec of the tropical cyclone.

Data were obtained from the U.S. Centers for Disease Control and Prevention (CDC), which included tropical storms and hurricanes. An alternate natural experiment was also conducted, in which tropical cyclones randomly affected the United States over time.

The precise date, location, and severity of tropical storms to populations was randomized. If mortality rates increased following the storms, researchers may conclude that the cyclones were likely to be the reason. Thus, this “reduced-form” method encompasses the potential ways in which tropical cyclones impact mortality without explicitly simulating each channel.
To estimate differences in state-level mortality each month throughout the 20 year period following each tropical cyclone, an econometric technique was used to identify the delayed impacts of tropical cyclones.

Fatality time-based series presented superpositions of numerous overlapping signals that represented a reaction to a specific tropical cyclone impact throughout the study period. These superimposing signals were isolated to deconvolute the fatality time series by experimentally retrieving the typical fatality impulse-response curve caused by one tropical cyclone impulse.

The Limited Information Cyclone Reconstruction and Integration for Climate and Economics (LICRICE) model was used to reconstruct the sequence of physical tropical cyclone events encountered by each state every month. These reconstructions resulted in estimates of the maximum wind speed experienced at each 0.125° × 0.125° ground pixel during each storm. This measure of tropical cyclone incidence significantly predicts physical damage and other economic and social repercussions globally.

Study findings

The United States National Oceanic and Atmospheric Administration (NOAA) reports that tropical cyclones resulted in an average of 24 direct deaths. However, after accounting for cascading consequences, tropical cyclones contributed to 7,170-11,430 indirect deaths.

Between 1930 and 2015, these cyclones caused 3.2-5.1% of deaths along the Atlantic coast.

Suicide, diabetes, sudden infant death syndrome, or unrecorded reasons caused about 59% of excess fatalities. Cardiovascular disease was the second leading cause of tropical cyclone-related excess mortality at 36% or 1.3 deaths, which was followed by cancer at 12% or 0.5 deaths.

A total of 50 deaths from tropical cyclones were among infants under 12 months of age, whereas 23 deaths were reported in individuals aged 65 years of age and older, in addition to 14 deaths reported in black populations. Importantly, increased excess fatalities may persist for up to 15 years after the tropical cyclone has occurred.

Tropical cyclones have a 2.8-fold higher death impact in unusual states than those where these storms more frequently occur. Thus, communities often adapt to their environment, which ultimately reduces the severity of comparable disasters.

Most tropical cyclone-related deaths occurred in southeastern states, including Florida, North Carolina, South Carolina, and Louisiana at 13%, 11%, 9%, and 8%, respectively. About 5.4 additional fatalities were calculated for every one m/sec increase in state-level wind speed over 172 months.

What causes excess mortality from tropical cyclones?

Several different factors contribute to the increasingly severe effects associated with tropical cyclones in CONUS. Recent climate shifts, for example, account for 12% of the trend, whereas population movement to coastal states and an aging CONUS population make up 7.5% and 80.5%, respectively.

Changes in social networks, such as the outmigration of working-age individuals, following cyclones may impact future health. Fiscal adjustments made by state or municipal governments may also influence future health outcomes, in addition to changes in the natural environment that arise following severe storms.

Conclusions

The study findings indicate that tropical cyclones may have a more adverse public health impact than previously considered, particularly among young or black individuals. However, the current study analyzed wind speeds and did not consider other features of tropical cyclones.

Future studies are needed to better understand the different factors that may contribute to the excess mortality associated with tropical cyclones, as this data can guide legislation to be more effective in response to these national disasters.