What is driving the massive and destructive rains across the country
Places across the country are facing more frequent and extreme rainfall over time — a reality laid bare once again by record rains and catastrophic flooding in eastern Kentucky and St. last week.
The warming atmosphere is fueling a number of weather-related disasters – wildfires, hurricanes, crippling heat waves. But since it also supplies once unthinkable amounts of rain in a single burst, the problem of such a rapid arrival of such a quantity of water poses serious challenges in a country where the built environment is not only outdated but of more and more outdated.
“The infrastructure we have is really built for a climate we no longer live in,” said Andreas Prein, a scientist at the National Center for Atmospheric Research (NCAR) who studies extreme rainfall.
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From populated cities to rural outposts, the United States has long struggled with antiquated sewer and wastewater systems, outdated bridges, and crumbling roads and culverts. But as more and more water falls from the sky faster in many places, these challenges have become even more pressing.
“What happened was more than the system — any system — can handle,” Metropolitan St. Louis Sewer District spokesman Sean Hadley said of recent storms that dumped more than 9 inches of rain in a few hours, breaking the previous daily record from 1915.
Record rain in St. Louis flooded storm drains and creeks. Sewage pumped back into homes. The Rivière des Pères grows beyond its banks. The region’s sprawling drainage systems, parts of which date back to the 19th century, were quickly overwhelmed.
“It was just too much water,” Hadley said.
An analysis of weather data by the nonprofit group Climate Central found that nearly three-quarters of the places the group looked at across the country saw an increase in the amount of rain falling on the wettest annual day since 1950. , especially along the Gulf Coast and the Middle. -Atlantic. Figures show that 2021 was a record year for extreme rainfall events, with dozens of places recording their wettest day in generations.
A separate report from Climate Central this spring found that of 150 sites analyzed by the group, 90% are now experiencing more average rainfall per hour, compared to 1970. These increasing bursts of extreme rainfall carry profound economic and health risks. human, such as those that have been exhibited more recently in eastern Kentucky.
Jen Brady, data analyst for Climate Central, said many places across the country are getting roughly the same rain or, in some cases, less rain per year than in the past. But it’s the sudden, incessant rains that contribute to flash flooding and other problems.
“The damage that occurs cannot be seen when you simply look [annual] rainfall records. It matters if you’re getting 2 inches per day versus 2 inches per hour,” Brady said. “Our infrastructure is not designed to hold so much water in such a short time.”
Scientists say there is little doubt what is driving the transition to more frequent and more devastating rains: climate change.
“Individual events happen all the time and have happened all the time in our history. We need to be aware that just because we have an event doesn’t mean it represents anything unusual,” Kenneth said. Kunkel, professor of atmospheric science at North Carolina State University.
But while it remains difficult for researchers to define the precise climate footprint of specific summer thunderstorms and other heavy rain events, they are increasingly able to detail the climate impact on tropical cyclones. massive events such as Hurricane Harvey. Moreover, after decades of observing and analyzing rainfall measurements across the country, Kunkel says the numbers clearly tell the story of change.
“There is no doubt that the frequency and intensity of extreme precipitation events are increasing,” Kunkel said, adding that the trend is particularly strong in the eastern and central United States.
“When I started 30 years ago, a [climate] signal was emerging,” he said. “This signal has become stronger and stronger. … The data is pretty definitive to show that.
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The explanation boils down to what Kunkel calls “basic physics”. For every degree Fahrenheit the air temperature increases, the atmosphere can hold about 4% more water.
The world has already warmed more than 1.8 degrees Fahrenheit (1 degree Celsius) since pre-industrial times. This increased heat means more moisture in the air – in the United States, much of which comes from the Gulf of Mexico – and more fuel for more intense thunderstorms.
“We’ve had an increase in the amount of atmospheric water vapor, … so we’re seeing more of these heavy precipitation events,” said David Easterling, a scientist with the National Centers for Environmental Information at the National Oceanic and Atmospheric Administration. “It’s all very consistent with the notion of a warming atmosphere.”
It’s not that St. Louis, for example, hasn’t had heavy torrential rains in the past. But these days, Easterling said, that same storm likely has access to a lot more moisture that can turn into torrential rain.
“What was really very unusual 100 years ago is no longer so,” he said.
After major flooding, Kentucky grapples with damage left behind
Heavier rains do not automatically translate into more flooding. It matters whether the ground where the rain falls is dry or already saturated, how populated the area is, and whether the water has a place to go.
In an urban area like St. Louis, the sheer amount of paved surfaces contributed to runoff that overwhelmed drainage systems. In eastern Kentucky, steep terrain has channeled cataclysmic amounts of water to flatter areas below where most homes and people are.
Irrespective of geography, more intense rainfall poses a major planning, engineering and adaptation challenge on the ground.
One problem is that the country’s flood mapping and rainfall data collection is underfunded and outdated, and has long relied on “a very patchwork approach,” said Chad Berginnis, executive director of the Association of State Floodplain Managers.
That means engineers, planners, and public works managers don’t always have access to the most accurate, up-to-date data on current risks — and those likely on the horizon.
Berginnis said some local governments with more resources — places such as Milwaukee, Nashville and Charlotte — have undertaken research to understand and plan for the water challenges they face. New York City has also invested in its own studies and measures to better protect against heavier rains and rising seas.
“They’re going to see less damage going forward,” Berginnis said. But not all places are so lucky.
“In rural areas or places that have less capacity, they’re stuck with the data available nationally, and it’s just not that good,” he said. “Unfortunately, it’s a bit of a haves and have nots in many cases.”
The problem of more frequent and extreme rainfall is not only national but also global. Europe experienced deadly flooding after heavy rains last summer. Parts of Australia have suffered huge rainfall in recent days, putting Sydney on track for its wettest year on record. Parts of China have seen devastating floods this summer, fueled by rainfall that, at least in one region, dumped 3.3 inches in a single hour.
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Torrents around the world show few signs of slowing down.
The federal government’s most recent National Climate Assessment found that over the coming century, “the observed increases in the frequency and intensity of heavy precipitation events over most parts of the United States are expected to continue. “. The largest increases in intense precipitation events have occurred — and are expected to continue — in the Northeast and Midwest.
“These trends are consistent with what would be expected in a warmer world, as increased evaporation rates lead to higher levels of water vapor in the atmosphere, which in turn lead to more frequent and intense extreme rainfall,” the scientists wrote.
That same assessment found that the country’s water supply systems “face considerable risks even without anticipated future climate changes.” But with the changes, the risk will increase for dams and levees at risk of failure, for landslides and erosion on the West Coast, for more flooding in low-lying areas in the Midwest and Southeast, and more pressure on old and overburdened infrastructure in the northeast.
For now, extreme precipitation events are likely only to become more extreme and more common unless the world makes rapid and drastic reductions in global warming emissions – which has yet to materialize.
Prein, the NCAR scientist, said that even if the world stops warming to 2 degrees Celsius (3.6 degrees Fahrenheit) beyond pre-industrial levels – a central goal of the Paris climate accord – the rains and flooding is likely to worsen further in the short term.
“We can’t just stop our greenhouse gas emissions immediately,” he said. “We will see these events become more intense over the next two decades, and there is not much we can do about it.”
This is why it is essential to invest in effective adaptation efforts and early warning systems, he said. The same goes for being more careful about where and how humans build new developments and manage existing infrastructure. Because the heavy rains will come.
“It’s sad but true,” he said, “those kinds of events are our new normal.”
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