New York City’s sinkhole surge is due to climate crisis, city official says

Sinkholes can often form after heavy rain

Last month, a large stretch of Radcliff Avenue in the Bronx borough of New York City collapsed, dropping a van into a newly formed sinkhole.

Sinkholes were on the rise in New York over the past year. And at a recent city council hearing, one local official pinned the underlying cause of the Bronx collapse and others like it on the climate crisis.

The Radcliff Avenue sinkhole reminds us that “we will not be able to change our infrastructure as fast as the climate is changing,” Rohit Aggarwala, commissioner of the city’s Department of Environmental Protection, told the hearing last week.

Sinkholes form after rock and dirt underground have dissolved, often from water. Eventually, when enough material has dissolved, the ground can no longer support the surface and a hole will collapse.

The collapses, also known as cave-ins, can also occur when pipes below a street break. Sinkholes can often be brought on by heavy rainstorms, which can saturate the groundwater and speed up erosion, as well as overstress pipes used for stormwater or sewage.

Until last year, sinkholes, also known as cave-ins, were actually becoming less frequent in New York City. In fiscal year 2019 (July 2018 – June 2019), the city recorded 3,769 sinkholes — down to 3,098 the following year, according to a city council report. By summer 2021, New York was down to 2,839 record sinkholes per year.

But between last July and June 2022, the city received 3,920 sinkhole complaints, Dr Aggarwala said in his testimony.

The commissioner pointed directly to the climate crisis as a driving force behind these infrastructure problems — particularly the impact that Hurricane Ida had on the city last year.

“During and the morning after Ida, of course, we saw the visible impacts of climate change on our infrastructure,” Dr Aggarwala said.

Hurricane Ida dropped over seven inches (18 centimetres) of rain on New York City, including over three in (8 cm) in just one hour over Central Park. Many parts of the city flooded, and more than a dozen people died.

Another storm last summer, Hurricane Henri, had dropped nearly 2 in (5cm) of rain in one hour a couple of weeks earlier.

Dr Aggarwala told the council that some parts of New York’s sewer system are only designed to handle 1.5 inches of rain per hour. Today, he said, the standard is 1.75 inches per hour — and they’re reevaluating that number.

Storms don’t have to be hurricanes to create problems either. The Radcliffe Avenue sinkhole formed after a short spate of heavy thunderstorms hit the city, the council report notes.

On 16 July this year, parts of the city saw up to 1.88 in of rain per hour — and then up to 1.64 in per hour just two days later, on 18 July, Dr Aggarwala told the council. The Radcliff Avenue sinkhole appeared the next day, 19 July.

Most sinkholes are not as dramatic as the recent one in the Bronx, though other large collapses have hit the city.

But these events — both large and small — point to the challenges of maintaining city infrastructure in a rapidly changing climate.

As the climate warms, storms are expected to become much more intense. That includes hurricanes like Ida and Henri, which climate scientists say will get stronger and wetter on a warmer planet.

That also includes more run-of-the-mill storms, however. Over the past couple of decades, more rainfall is hitting in “intense single-day events”, according to the US Environmental Protection Agency (EPA).

There are things officials can do to mitigate risk, like looking for weaknesses in the sewer system, Dr Aggarwala said. And many of the sewer lines in the Bronx were built in a way that hasn’t stood up particularly well to stronger storms, he adds.

But the Radcliff Avenue sinkhole is a reminder that the climate crisis can “take us by surprise,” the commissioner added.

Beyond adapting to the new climate reality, the city should also be working to stem the drivers of the climate crisis, he said.

“When you’re in a hole, the first thing to do is stop digging,” Dr Aggarwala said. “Which is why it is so important that we reduce our greenhouse gas emissions.”