Extreme rain is a growing climate threat to the northeastern US

As high temperatures break records in the US and wildfires sweep across the West, another climate-driven weather hazard – extreme rain – is hitting the Northeast and scientists say it will get worse as the climate changes. This will bring more rain-induced flooding to an unprepared region of millions.

The most recent example occurred on August 18, when a slow-moving storm system approached the northeastern Great Lakes states. An area of ​​low pressure over Connecticut and New York pulled all that moist air up, creating perfect conditions for rain. The remnants of Hurricane Ernesto have also arrived, slowing the movement of air masses in the region in a sort of “traffic gridlock,” according to AccuWeather Inc.

“The situation itself was not that unusual,” said Tom Kines, senior meteorologist at AccuWeather. “It just happened to be the kind of worst-case scenario where you get strong storms in one area for a long period of time.”

The result was anything but ordinary. Within 12 hours, the area saw two 1,000-year rainfall events — events that have a 0.1 percent annual chance of occurring — just 35 miles apart.

“Some areas have had two or three months worth of rain,” Kines said.

Particularly hard hit were southwestern Connecticut and north-central Long Island, where rain fell at a rate of 3.5 inches per hour in some places. In Connecticut, two people died and more than 100 needed rescue.

Two precipitation stations in Oxford, Connecticut, showed 24-hour totals of 14.83 inches (37.67 centimeters) and 13.5 inches. A committee is evaluating the measurements, which, if validated, would surpass the existing state record of 12.77 inches set on Aug. 19, 1955, during Hurricane Diane.

Parts of Long Island saw flash flooding from more than 9 inches of rain, and northern New Jersey was drenched with lesser amounts.

The storms extracted fuel from an environment that has changed dramatically since records began in the area in the late 19th century. The whole world is on average 1.3 C warmer. For every 1C rise, air can hold up to 7% more water.

Intensification of extreme precipitation has increased in accordance with this basic relationship between heat, air and water. This is why, when the right conditions line up, it often rains more than in past decades.

“As water vapor increases, heavy precipitation increases,” said climate specialist David Easterling, chief of the Climate Assessment Division at the US National Oceanic and Atmospheric Administration.

And it’s doing so in the Northeast faster than anywhere else in the U.S., according to the Fifth National Climate Assessment, released last year. Precipitation is higher throughout the year, and the worst of it has increased by 60% over six decades. The latest United Nations climate report noted a marked increase in extreme precipitation in North America, amid greater frequency and magnitude globally.

The most extreme precipitation in the northeast shows the fastest increase. Days with more than 5 inches increased by 103%. Most of it comes during the warm seasons, sometimes in the form of cyclones or bad weather left over from them, rather than snow, which parts of the region see less and less of.

And these charts only show concentrated, short-term events. “We also need to look at multi-day events where different types of storm systems lead to rain or precipitation that falls almost consistently over two to three days,” said Lesley-Ann Dupigny-Giroux, Vermont State Climatologist.

Ways to protect people are not keeping pace with this pace of change. Vermont alone experienced devastating flash flooding both this summer and last — despite advanced flood preparations undertaken after 2011’s catastrophic Hurricane Irene.

Damage from storms caused by wind or hail has seen “a very significant increase” in recent years, said Steve Bowen, chief scientific officer at Gallagher Re. Flood events are more likely to fluctuate depending on what phase the Pacific Ocean is in – El Niño, La Niña, or neutral.

Read more: Giant hail is the weather threat keeping insurers awake at night

Almost all flood insurance in the US is provided by the government’s National Flood Insurance Program, but it only covers 12% to 14% of annual flood damage. From 1978 to 2015, New Jersey and New York received more payments than all but two other states. However, region-wide, northeastern coastal counties only have about 6.5% flood insurance, and inland counties, which are at greater risk of flash flooding than ever before, have a rate of 1 .5%.

That means one of the most dangerous symptoms of climate change will come for a highly developed (read: paved) region where people living outside nationally designated areas face no mandate to buy flood insurance and , I generally don’t.

Insurance is how individuals protect themselves. Planning and engineering is how communities do it, and they currently have insufficient tools: The US precipitation frequency estimates used for planning, called Atlas 14, are based on historical data and have been pieced together over time . Engineers need up-to-date estimates of future precipitation to know what specifications to build.

Read more: The risky business of predicting where climate disaster will strike

The US is working on its ability to predict what’s coming. The Bipartisan Infrastructure Act of 2021 authorized spending for the first time to update the Project Climate Change Atlas and estimate precipitation frequency across the US. Atlas 15 is expected to be completed by 2027.

Even so, the Department of Defense did not want to wait. For a Pentagon-funded project, Easterling and colleagues built an online tool that displays Atlas 14 results and then 10-year projections from 2025 to 2085. Two military installations about 70 miles east and west of Oxford, Connecticut, where triggered last week’s storm. the most rain, each could see an increase in peak precipitation of an inch or more by 2045.

Cyrena Arnold is director of product marketing for weather and climate data provider Atmospheric G2. A meteorologist and storm chaser, she also makes explainer videos on TikTok, including an analysis of the recent storm centered in Connecticut.

“People say, ‘Oh my God, I’ve never seen this kind of weather before. I’ve never had that before,’” said Arnold, who lives in New Hampshire. She often tells them that today’s weather in New England is what used to be normal weather a few degrees of latitude south: “That’s how it was down there 20-30 years ago. And now it’s happening up here.”

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