extreme weather

How is climate change connected to flooding?

A woman looks on at floodwater during heavy rainfall in Miami, on May 26, 2020. Credit: Chandan Khanna/AFP via Getty Images
A woman looks on at floodwater during heavy rainfall in Miami, on May 26, 2020. Credit: Chandan Khanna/AFP via Getty Images

Flooding has existed for millennia. What’s different now is a global population of more than 7.8 billion people, most living in a built environment that can make flooding worse, and forces of climate change that are increasing the risks from flooding.

There are different kinds of floods. Rivers can swell and overflow their banks, inundating whatever is located in a flood plain. Hurricanes and tropical storms can push coastal waters inland, the surge swallowing homes and businesses. Torrential downpours in cities, with their vast areas of hard surfaces like roads, parking lots and rooftops, can overwhelm stormwater management systems, prompting a need for water rescues. Dams can break.

Scientists say climate change can affect all these kinds of flooding disasters, raising risks and costing lives.

Take coastal flooding. The Fourth National Climate Assessment in 2018 by the U.S. government found that global average sea level has risen by about 8 inches since 1900, with almost half since 1993. As sea level rises, so does the prevalence of sunny day flooding, powered by the tides. In July 2021, the National Oceanic and Atmospheric Administration reported high-tide or sunny day flooding had doubled over 20 years, setting records, and was expected to be common along mosts American coasts by 2030

Rising seas also mean hurricanes or tropical storms can push a higher wall of water into inhabited coastal areas, making storm surge more deadly. The climate assessment predicted that sea levels would continue to rise by at least several inches in the next 15 years and by one to four feet by 2100.

Climate change has also energized extreme weather, providing a new awareness of terms like “rain bombs” and “atmospheric rivers.” While flooding can have effects across the economic spectrum, a National Academies of Sciences, Engineering and Medicine report on urban flooding from 2019 found that “poor, racial and ethnic minorities, the elderly, renters, non-native English speakers, and those with mobility challenges were disproportionately affected.”

According to the National Oceanic and Atmospheric Administration, a 1 degree Fahrenheit rise in temperature equals as much as a 4 percent increase in atmospheric water vapor. And an atmosphere with more water vapor can make more precipitation, says Deke Arndt, a top scientist with NOAA. “The biggest events are getting bigger, and big rain is taking up more of our annual rainfall budget,” Arndt notes.

The experts say it’s only going to get worse, as more people move to risky coastal areas, crowd into floodplains and rely on stormwater management systems that were not built with climate change in mind. “Heavy rainfall is increasing in intensity and frequency across the United States and globally and is expected to continue to increase,” the climate assessment concluded. 

— James Bruggers

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