New York City’s future is very wet

New York City saw it coming. In May, in the kind of clarifying document that invariably gets noticed when it’s too late, the city mapped out the sort of devastation that Hurricane Ida would bring just a few months later.
The message of the New York City Stormwater Resiliency Plan is that, weatherwise, the scale of everything has changed. The city’s current infrastructure — its roads, subway tunnels, sewer systems, storm drains — is not built to withstand the climate-related ravages to come.
As a result, the report states, capital investments “provide diminishing returns, as it becomes more and more challenging to treat the large volumes of stormwater released in extreme events.”
Ida put an exclamation point on realities that New York was already grappling with. Like other parts of the world, the report notes, the city is confronting not just calamitous extreme events like the inundations of Ida. It’s the drip, drip of “the chronic worsening of average conditions.”
That beautifully concise yet elastic phrase sounds like the title of a Russian novel. Our current world was constructed to manage one kind of average, with extremes appropriately measured by their distances from that mean. But the chronic worsening of average conditions means that the extremes are growing ever more distant and ever more dangerous.
For example: The city’s sewage system is geared to handle about 1.75 inches of rain per hour. On September 1, between 8:51 and 9:51 pm, Ida brought down 3.15 inches in Central Park.
Even on dry days, subterranean New York is a soggy, messy place, with leaking sewer pipes and creaky water mains. Yet even if all had worked perfectly on September 1 — if every storm drain had been clear and every pipe in New York City’s 7,400-mile sewer system had been free of obstruction — the city simply had no way to rid itself of so much water.
And since about 60% of the city’s pipes combine stormwater runoff with sewage, it’s not just water that backs up when capacity is surpassed.
“Rainfall rates were really extraordinary and far exceeded the capacity of the system,” Department of Environmental Protection Commissioner Vincent Sapienza said at a briefing after the storm. “Anything over two inches an hour we’re going to have trouble with.” According to the New York City Panel on Climate Change, by the end of the 21st century, the city could experience as much as 25% more annual rainfall. The number of days marked by extreme rain would also markedly increase.
New York will undoubtedly have to spend billions to deal with water. But it may not be able to buy its way out of trouble without also changing its ways.

—Bloomberg