A new study revealed tat tropical cyclones in the contiguous United States may have been responsible for 3.6 to 5.7 million excess deaths between 1930 and 2015, significantly surpassing official government estimates.

In the study, published in Nature, investigators used advanced statistical methods to uncover previously overlooked long-term mortality impacts in disaster assessments. The findings suggested the tropical cyclone climate may be a major driver of mortality risk across the United States, particularly among vulnerable populations.

The investigators found that the average tropical cyclone (TC) generated between 7,000 and 11,000 excess deaths compared with 24 immediate deaths reported in official statistics, and TC-related mortality persisted for up to 15 years following each event. The investigators noted that tropical cyclone climate in the contiguous United States (CONUS) contributed to 3.2% to 5.1% of all deaths during the study period, and infants and Black individuals were disproportionately affected.

The investigators analyzed the impact of 501 tropical cyclones on mortality rates across the CONUS using a deconvolution technique. They employed the Limited Information Cyclone Reconstruction and Integration for Climate and Economics (LICRICE) model to estimate maximum wind speeds experienced at each location during storms. This data was linked to monthly state mortality records from the U.S. Centers for Disease Control and Prevention.

The econometric analysis accounted for several factors, including average differences across states, state-specific seasonal patterns, nonlinear state-specific trends, national month-of-sample effects, state-by-month-specific linear trends, and state-specific nonlinear effects of temperature on mortality.

The investigators identified a systematic increase in excess mortality that persisted for 172 months (14.3 years) following a tropical cyclone. In the month of landfall, monthly mortality rates increased by 0.033 deaths per 100,000 population per m/s of state-level wind speed incidence. For each 1 m/s of state-level wind speed incidence, the investigators estimated an average cumulative 5.37 excess deaths per 100,000 over 172 months.

Infants under 1 year of age were the most vulnerable, with 49.8 excess deaths per 100,000 per m/s, followed by those aged 65 years and older with a rate of 22.8 excess deaths per 100,000 per m/s. Black individuals experienced a cumulative excess mortality risk of 13.53 per 100,000 per m/s over 172 months compared with 4.19 for White individuals.

While 36% of TC-related excess deaths were attributed to cardiovascular disease, 58.9% were attributed to "other" causes. States with infrequent tropical cyclone exposure exhibited higher vulnerability, with 10.4 deaths per 100,000 per m/s after 172 months compared with 3.49 in more frequently affected states. An acceleration in TC-related mortality was observed after 2001, with an increase from +9.2 TC-related deaths per month before 2001 to +43.3 deaths per month after 2001.

The investigators concluded that the tropical cyclone climate is a significant driver of mortality risk in the United States, particularly among infants, individuals aged 1 to 44 years, and Black individuals. They called for further research to better understand the mechanisms behind these delayed mortality effects and to develop interventions that mitigate the long-term health impacts of tropical cyclones.

While the study highlighted the widespread mortality burden of tropical cyclones, the investigators acknowledged several limitations, including the use of wind speed as the primary measure of TC incidence, the lack of granular demographic data for the entire study period, and the inability to account for migration patterns following tropical cyclones. Despite these limitations, the findings pointed to the need for better strategies to address the critical health care needs of populations affected by tropical cyclones.

The authors declared no competing interests.