What is driving the massive and devastating rainfall across the country


At a weather station in Fairbanks, Alaska, hourly precipitation is about 50 percent More intense, on average, than it was half a century ago. The Wichita area is seeing 40 percent more precipitation these days. Huntington, W. Fa, and Sioux City, Iowa, are experiencing floods that are nearly 30 percent more extreme than they were in 1970.

Places across the country experience more frequent and extreme precipitation over time — a reality that was once again revealed by record-breaking rains and catastrophic flooding in eastern Kentucky and St. Louis last week.

The Supercharged warming atmosphere Any number of weather-related disasters – wildfires, hurricanes, crippling heat waves. But because it also feeds unimaginable amounts of rain in one go, the problem of so much water arriving so quickly poses serious challenges in a country where the built environment is not only outdated but increasingly outdated.

“The infrastructure we already have is built for a climate we don’t live in anymore,” said Andreas Brin, a scientist at the National Center for Atmospheric Research (NCAR) who studies extreme precipitation.

How two rain events every 1 in 1,000 years hit the United States in two days

From populated cities to rural outposts, the United States has long struggled with old sewer and sewage systems, old bridges, and dilapidated roads and canals. But with more water falling from the sky more quickly in many places, those challenges are becoming more pressing.

“What happened was a lot more than the system — any system — could handle,” Sean Hadley, a spokesman for the Metropolitan St. Louis Sewer District, said of the recent storms that dumped more than 9 inches of rain there within hours. The previous daily record is from 1915.

Record massive rain in St. Louis flooded rainwater drains and streams. Consolidation of sewage water in homes. The Des Perez River swelled beyond its banks. The area’s sprawling drainage systems, parts of which date back to the 19th century, were soon overrun.

“It was just a lot of water,” Hadley said.

that Analytics From weather data by the nonprofit Climate Central Group it found that nearly three-quarters of the locations the group examined across the country had experienced an increase in the amount of rain falling on their wettest annual day since 1950—particularly along the Gulf Coast and the mid-Atlantic. . The numbers show that 2021 was a record year for extreme precipitation events, with dozens of places recording their wettest day in generations.

a separate central climate report This spring it found that of the 150 sites the group analyzed, 90 percent are now seeing more average rain per hour, than they did in 1970. Those increased eruptions of intense rain carry profound economic and human health risks, the likes of which were recently shown in Kentucky. Eastern.

Many places across the country are seeing roughly the same, or in some cases, less rainfall annually than they have in the past, said Jane Brady, a data analyst with Climate Central. But it is the sudden, relentless rainfall that contributes to flash floods and other problems.

“The damage done doesn’t show when you just look. [annual] precipitation records. “It’s important to get two inches a day, as opposed to two inches an hour,” Brady said. “Our infrastructure is not designed to hold that much water for that long.”

Scientists say there is little doubt about the driver behind the shift toward more frequent and destructive rain: climate change.

Individual events happen all the time and they happen all the time in our historical record. “We have to realize that just because an event exists doesn’t mean it represents something unusual,” said Kenneth Kunkel, professor of atmospheric sciences at North Carolina State University.

But while it remains difficult for researchers to determine the exact climate footprint on specific summer thunderstorms and other heavy rain events, they are increasingly able to detail the impact of climate on massive tropical cyclones like Hurricane Harvey. What’s more, after decades of observing and analyzing rainfall gauges across the country, Kunkel says the numbers tell a clear story of change.

“There is no doubt that the frequency and intensity of extreme precipitation events are increasing,” Konkel 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 showing.” This signal became stronger and stronger. … the data is very crucial to show that.”

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The explanation boils down to what Kunkel calls “basic physics.” For every degree Fahrenheit that the air temperature increases, the atmosphere can hold about 4 percent more water.

The world has already warmed by 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 rainstorms.

“We’ve seen an increase in the amount of water vapor in the atmosphere, … so we’re seeing more heavy precipitation events,” said David Easterling, a scientist at the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information. “It all fits perfectly with the idea of ​​a warm weather.”

It’s not that St. Louis, for example, hasn’t had heavy rainstorms in the past. But these days, Easterling said, that same storm will likely get to so much moisture that it can turn into torrential rain.

“What was really unusual 100 years ago is not unusual anymore,” he said.

After major floods, Kentucky is struggling with the damage left behind

More heavy rain alone does not automatically translate into more flooding. It is important whether the soil in which the rain falls is dry or already saturated, how crowded the area is and whether the water has somewhere to go.

In an urban area like St. Louis, the massive amount of paved surfaces contributed to the runoff that overwhelmed the sewage systems. In eastern Kentucky, the steep terrain has pushed huge amounts of water into the flat areas below, where most of the homes and people are.

Regardless of geography, heavy rainfall poses a major planning, engineering and adaptation challenge on the ground.

One problem is that the country’s maps of floods and collection of rainfall data are underfunded and outdated, and have long relied on a “too patchy approach,” said Chad Bergenis, executive director of the state’s Association of Floodplain Managers.

This means that engineers, planners and public works officials do not always have access to the most accurate and up-to-date data about current risks — and those most likely on the horizon.

Bergenis said some local governments with more resources — places like Milwaukee, Nashville and Charlotte — have conducted research to understand and plan for water-related challenges. New York City has also invested in its own studies and in measures To better withstand itself against heavy rainfall and rising seas.

“They will see less damage in the future,” Bergenis said. But not everyone is so lucky.

“In rural areas or places that have less capacity, they are stuck with the data that is available nationally, which is not good,” he said. “Unfortunately, it’s kind of have-and-have-not in many cases.”

The problem of intense and frequent precipitation is not only a national problem, but also a global one. Europe experienced fatal floods After a heavy rain last summer. Parts of Australia have suffered heavy rain in recent days, putting Sydney on track for the wettest year ever. Parts of China have been hit by devastating floods this summer, fueled by rains that, in at least one region, lying 3.3 inches in one hour.

Summer floods and heat waves in China are fueling climate change plans

Across the world, torrents are showing few signs of slowing down.

The most recent National Climate Assessment by the federal government found that, over the next century, “observed increases in the frequency and intensity of heavy rainfall events are expected to continue in most parts of the United States.” The largest increases in extreme precipitation events occurred – and are expected to continue – in the Northeast and Midwest.

“These trends are consistent with what would be expected in a warmer world, where increased evaporation rates lead to higher levels of water vapor in the atmosphere, which in turn increases the frequency of intense precipitation,” the scientists wrote.

The same assessment found that the country’s water systems “face significant risks even without projected future climate changes.” But with changes, the risk will rise to dams and levees at risk of collapsing, landslides and erosion on the West Coast, more flooding in low-lying areas in the Midwest and Southeast, and more pressure on aging and cumbersome infrastructure in the Northeast.

Currently, extreme precipitation events are likely to become more extreme and more common unless the world makes rapid and drastic reductions in emissions that are heating the planet – something that has yet to be achieved.

Brin, the NCAR scientist, said that even if the world stopped warming at 2 degrees Celsius (3.6 degrees Fahrenheit) past pre-industrial levels – a key goal of the Paris climate agreement – rain and flooding events are likely to get worse in the near term. .

“We cannot stop greenhouse gas emissions immediately,” he said. “We will see these events become more severe in the next two decades, and there is not much we can do about it.”

This is why it is so important to invest in effective adaptation efforts and early warning systems, he said. So, more caution about where and how humans build new developments and manage existing infrastructure. Because heavy rain will come.

“It’s sad but true,” he said, “these kinds of events are our new normal.”

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