What is driving massive and destructive rains across the country

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At a weather station in Fairbanks, Alaska, every hour of rain is on average about 50 percent more intense than it was half a century ago. The Wichita area is experiencing about 40 percent more rainfall these days. Huntington, W.Va., and Sioux City, Iowa, are seeing approximately 30% more extreme floods than in 1970.

Places across the nation are facing more frequent and extreme rainfall over time, a reality laid bare once again by record rains and catastrophic floods in eastern Kentucky and St. Louis last week.

The warm atmosphere is overloading any number of climate-related disasters: fires, hurricanes, crippling heat waves. But because it also feeds once-unthinkable amounts of rain in single gusts, the problem of so much water arriving so quickly is posing serious challenges in a nation where the built environment is not only obsolete but increasingly outdated.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.

Like two 1 in 1,000 rain events hit the United States in two days

From populated cities to rural outposts, the United States has long struggled with antiquated sewer and sewage networks, outdated bridges, and crumbling roads and culverts. But as more water falls from the sky faster in many places, these challenges have only become more urgent.

“What happened is a lot more than the system – any system – can handle,” said Sean Hadley, a spokesman for the St. Louis Metropolitan Sewer District, of the recent storms that dumped more than 9 inches of rain there. a few hours. breaking the previous daily record of 1915.

Record-breaking rain in St. Louis flooded drains and creeks. The sewage spilled into the houses. The River des Peres swelled beyond its banks. The area’s extensive drainage systems, some of which date back to the 19th century, were quickly overwhelmed.

“It was just too much water,” Hadley said.

An analysis of meteorological data by the non-profit group Climate Central found that nearly three-quarters of the locations surveyed by the group across the country experienced an increase in the amount of rain falling on the wettest day since 1950, particularly long. the Gulf Coast and Mid-Atlantic. The numbers show that 2021 was a record year for extreme rainfall events, with dozens of places having the wettest day in generations.

A separate report from Climate Central this spring found that of the 150 locations analyzed by the group, 90% now experience more average rainfall per hour than in 1970. Those increasing bursts of extreme rainfall carry profound economic and human health risks, similar. to which they were most recently on display in eastern Kentucky.

Jen Brady, a data analyst for Climate Central, said that in many places in the country it rains about the same, or in some cases, less rain every year than in the past. But it is the sudden and incessant rains that are contributing to flash floods and other problems.

“The damage that’s happening doesn’t show itself when you look at it [annual] rainfall record. It matters if you get 2 inches a day versus 2 inches an hour, “Brady said.” Our infrastructure isn’t designed to hold that much water in that long.

Scientists say there is no question about what is driving the shift towards more frequent and devastating rains: climate change.

“Individual events happen continuously and have happened continuously in our historical record. We need to be aware that just because we have an event doesn’t mean it represents something unusual, ”said Kenneth Kunkel, professor of atmospheric science at North Carolina State University.

But while it remains difficult for researchers to delineate the precise climate footprint on specific summer thunderstorms and other heavy rain events, they are increasingly able to detail the climate impact on massive tropical cyclones such as Hurricane Harvey. Additionally, after decades of observing and analyzing rainfall metrics across the country, Kunkel says the numbers tell a clear story of change.

“There is no question that the frequency and intensity of extreme rain 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] the signal was emerging, “he said.” That signal just got stronger.… The data is pretty definitive in proving it.

‘They’re not slowing down’: the rise of billion-dollar disasters

The explanation boils down to what Kunkel calls “basic physics”. For every degree Fahrenheit of air temperature rise, the atmosphere can contain about 4% more water.

The world has already warmed over 1.8 degrees Fahrenheit (1 degree Celsius) since pre-industrial times. This increase in heat means more humidity 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 rain events,” said David Easterling, a scientist at the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information. “All of this is very consistent with the idea of ​​a warm atmosphere.”

It’s not like St. Louis, for example, hasn’t had severe thunderstorms 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 unusual,” he said.

After severe flooding, Kentucky is grappling with the damage left behind

More intense rains alone don’t automatically translate into more floods. It matters if the ground where the rain falls is dry or already saturated, how populated the area is, and if the water has nowhere to go.

In an urban area like St. Louis, the sheer amount of paved surfaces contributed to the runoff that engulfed the drainage systems. In eastern Kentucky, the steep terrain has funneled catastrophic amounts of water into the flatter areas below, where most homes and people are located.

Regardless of geography, the heaviest rains pose a major planning, engineering and adaptation challenge on the ground.

One problem is that the country’s flood mapping and rainfall data collection are underfunded and outdated and have long been based on “a very piecemeal approach,” said Chad Berginnis, executive director of the Association of State Managers of the Plains. alluvial.

This means that engineers, planners and public works officials don’t always have access to the most accurate and up-to-date data on current and likely risks on the horizon.

Berginnis said some more resourceful local governments – places like Milwaukee, Nashville and Charlotte – have undertaken research to understand and plan the water-related challenges they face. New York City has also invested in its studies and measures to better protect itself from the heaviest rains and rising seas.

“They will see less damage going forward,” Berginnis said. But not all places are so lucky.

“In rural areas or places that have lower capacity, they are stuck with nationally available data, and they just aren’t that good,” he said. “Unfortunately, in many cases they are haves and haves.”

The problem of the most frequent and extreme rainfall is not only national but also global. Europe suffered deadly floods after heavy rains last summer. Parts of Australia have experienced tremendous rainfall in recent days, putting Sydney on track for its wettest year on record. Parts of China experienced devastating flooding this summer, fueled by rainfall that, in one area at least, discharged 3.3 inches in a single hour.

China’s summer floods and heatwaves fuel plans for a changing climate

Around the world, torrents show little sign of slowing down.

The federal government’s most recent National Climate Assessment found that, over the next century, “the observed increases in the frequency and intensity of heavy rainfall events in most of the United States are expected to continue.” The largest increases in heavy rainfall 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 leads to more frequent and intense extreme rainfall.” , the scientists wrote.

The same assessment found that the nation’s water systems “face considerable risks even without anticipated future climate change.” But with changes, the risk will increase from failing dams and levees, landslides and erosion on the west coast, further flooding in the lower Midwest and Southeast areas, and increased pressure on old and overloaded infrastructure in the United States. North East.

For now, extreme precipitation events are likely to only become more extreme and more common unless the world rapidly and drastically reduces 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 key goal of the Paris climate agreement – events are likely of rain and flood will get worse in the short term.

“We can’t just shut down our greenhouse gas emissions immediately,” he said. “We will see these events become more intense over the next two decades and there is very little we can do about it.”

That’s why investing in effective adaptation efforts and early warning systems is essential, he said. So it is to be more cautious 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, “these kinds of events are our new normal.”

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