Jeff Masters Weather Blog

What new data reveal about how hurricanes kill » Yale Climate Connections

On Tuesday, new research released by the National Hurricane Center underscored the threat posed by water in hurricanes — finding that over the past decade, rainfall flooding has accounted for nearly 60% of all U.S. deaths from tropical cyclones.

Though previous research concluded storm surge — seawater pushed ashore by the strong winds of a hurricane — accounted for nearly half of all U.S. tropical cyclone deaths from 1963-2012, since 2013 storm surge has been responsible for only about one in 10 direct hurricane fatalities.

During the more recent period, Hurricane Ian in 2022 caused 41 of the 50 (82%) storm-surge-related deaths since 2013. And 2017’s Hurricane Harvey, despite causing more direct deaths than any hurricane included in the latest study, accounted for only 25% of all rainfall-induced flooding deaths over the past decade. The new numbers indicate the tropical cyclone rainfall threat is prolific — regardless of storm intensity and hurricane category — and less tied to episodic catastrophic hurricanes like Ian.

two pie charts show that hurricane-related freshwater flooding killed more than twice as many people during the past 10 years than it did before 2013
Graphic: Michael Lowry

Inland flooding can catch people unaware

The inland flooding impacts from tropical cyclones have been front-and-center in recent years. Hurricane Matthew in 2016 and Hurricane Florence in 2018 caused extensive inland flooding and dozens of deaths from heavy rainfall, which filled river basins across multiple states. In many cases, major flooding in the aftermath of a hurricane can peak days after landfall and hundreds of miles away from the initial point of landfall. The delayed impact outside the immediate forecast cone can prove especially dangerous for those unprepared on the periphery.

Climate change is worsening the threat of heavy rainfall from tropical cyclones. Numerous studies project rainfall rates in Atlantic tropical cyclones will increase by 10-20% from a 2°C global warming. The more intense rainfall is colliding with population booms in coastal communities to exacerbate the dangers of extreme rainfall flooding, especially on the outskirts of tropical cyclones where populations are less prepared.

a chart lists the deadliest U.S. hurricanes (direct deaths). No. 1 was Hurricane Katrina, which killed as many as 822 in 2005.
Graphic: Jeff Masters

Although forecast rainfall totals are often conveyed to the public, the intense rate of rainfall unique to tropical cyclones and preexisting river levels and soil conditions are often more important indicators for potential flooding from heavy rainfall. The National Weather Service encourages the public to consult its Excessive Rainfall Outlook product, which includes many of these considerations, for guidance on potential flash flooding.

Water kills much more often than wind

Almost nine in 10 direct deaths from tropical cyclones over the past 10 years were attributed to water. In addition to freshwater (rainfall) flooding deaths (57%) and storm surge deaths (11%), 15% of all direct deaths were from high surf and ocean rip currents — powerful channels of water that can pull even the strongest swimmers away from shore — a significant increase from 6% in earlier findings. Deadly rip currents can happen far away from hurricanes and in the wake of a hurricane’s passing when skies clear and beachgoers return to the water.

Wind-related and tornado-induced deaths from tropical cyclones continue to account for only a small share (about one in 7) of hurricane-related fatalities.

Hurricanes also kill indirectly

Experts also reiterated the significance of pre- and post-storm threats from tropical cyclones in their study update. Indirect deaths — those not from trauma incurred by a direct hurricane force like wind-borne debris or flooding — were nearly as high as deaths directly tied to hurricane hazards.

a chart lists the deadliest U.S. hurricanes (direct and indirect deaths). No. 1 was Hurricane Maria, which killed as many 2,981 in 2017. Katrina ranks No. 1 with more than 1,000 deaths.
Graphic: Jeff Masters

Indirect deaths can occur for a variety of reasons. The most common causes of indirect deaths since 2013 have been traffic accidents (16%), preparation/cleanup accidents (15%), carbon monoxide poisoning (12%), lack of medical care (11%), power problem/electrocution (11%), and post-storm heat (9%). Traffic accidents — the most common cause of indirect deaths in recent years — often occur in association with downed trees or where traffic signals are inoperable in the wake of a storm.

The authors note that mortality data from Hurricane Maria in 2017 were not included in its most recent update, because no distinction was made between direct and indirect deaths in data used for the nearly 3,000 fatalities identified by a 2018 excess mortality study conducted by the George Washington University’s Milken Institute School of Public Health.

The study authors — including National Hurricane Center Director Michael Brennan — are in the process of merging the latest data with results from previous studies for a comprehensive picture of long-term deaths from tropical cyclones in the United States.

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