FORT LAUDERDALE, Fla. -- Ask anyone the most dangerous element of a hurricane, and they may mention wind. They may mention storm surge. But they're unlikely to name the biggest current killer: rain.
In the past three years, as the impact of climate change on hurricanes became more apparent, rain has pushed aside storm surge to emerge as the top source of deaths.
About 75% of the 162 fatalities in hurricanes and other tropical cyclones striking the United States from 2016 to 2018 were caused by rain-induced flooding, with most victims drowning in or near their vehicles, according to the National Hurricane Center. The number excludes the toll from Hurricane Maria, which dumped enormous quantities of rain on Puerto Rico, because of uncertainties in the death count.
The fatalities occurred in a series of particularly wet hurricanes that set state and national rainfall records. Topping these was Hurricane Harvey, a 2017 storm that brought more than 60 inches of rain to parts of southeastern Texas, setting a U.S. record for tropical weather systems. Torrents of water swept away cars, carried off drivers attempting to escape on foot, and threw vehicles off low-lying bridges.
Such scenes may become more common as heavier rain pours from hurricanes forming in a warmer world.
"I think we're at the beginnings of the new normal," said Ben Kirtman, director of the Center for Computational Science Climate and Environmental Hazards Program at the University of Miami's Rosenstiel School for Marine and Atmospheric Science.
"It's pretty simple. A warmer atmosphere holds more water vapor. And so when it comes time to condense all that water vapor and produce rainfall, there's more water vapor available. The second element is the engine for tropical storms; the energy source for that engine is warm ocean surface temperatures, and those have risen. As the climate system warms, the ocean warms. That means there's more fuel for these hurricanes, which can lead to enhanced rainfall."
Several studies attribute Harvey's torrential rain at least partly to climate change. A 2017 study by scientists at the Lawrence Berkeley National Laboratory found that climate change probably increased the hurricane's rains in the Houston area by up to 38 percent.
A study by scientists at the National Center for Atmospheric Research and other institutions found a direct link between Harvey's rain and the unusual amount of heat in the Gulf of Mexico at the time, when the water temperate reached 86 degrees. The study, funded by the U.S. Department of Energy and National Science Foundation, linked the amount of rainfall directly to the quantity of water that evaporated from the Gulf of Mexico, showing that the heat lost from the ocean manifested itself in the amount of water that fell as rain.
"While hurricanes occur naturally, human-caused climate change is supercharging them and exacerbating the risk of major damage," the study said. " ... Harvey could not have produced so much rain without human-induced climate change. Results have implications for the role of hurricanes in climate. Proactive planning for the consequences of human-caused climate change is not happening in many vulnerable areas, making the disasters much worse."