"In a world without people, how fast would NYC fall apart? Here’s the timeline."

As noted in the introduction to 2022's "Iran Says Its Ballistic Missiles Have the Capability Of “Turning New York Into Hellish Ruins”": 

After Mayor de Blasio that may not be the threat the Mullahs Ayatollahs think it is. 

From Popular Science, June 5:

In a week, mold moves in. In a century, New York is a forest. 

Imagine the ceaseless cacophony of New York City suddenly stopped. No sirens wailed. No cars zoomed. No subways rumbled beneath sidewalks. All eight million New Yorkers disappeared overnight. 

Now, imagine what would happen next. If no one’s around to sweep the sidewalks, weed Central Park, or turn the power grid on, nature would move in—and quick. Dandelions would spring up in asphalt cracks. Raccoons would move into abandoned apartments. Sidewalk trees would outgrow their planters. 

But just how swiftly would the city disappear beneath a curtain of green? We talked to architects and urban ecologists to map out a potential timeline.

From Day 1 To Month 1: Plunged Into Darkness 
With no one to maintain the power grid, the Big Apple would go dark within a few days. The Milky Way would illuminate Midtown as light pollution disappears overnight. Without air conditioning and heat, “you start getting weird temperatures inside the building. Mold starts to form on the walls,” says architect Jana Horvat of the University of Zagreb, who studies building decay.

Some green energy projects in the city might stay lit for longer, such as the solar and wind-powered Ricoh Americas billboard in Times Square. Eventually, though, even the Ricoh billboard would go dark; not because the billboard would lose power, but because there would be no one to replace its LED lightbulbs. 

Without power, the pump rooms that clear out 13 million gallons of water daily from the subway would be useless, and the train tunnels would begin to flood. “Probably this water would result in [the subway] being, you know, occupied by new species,” says Horvat. “Some plants would start growing, some animals” would move in. Likely, species that already thrive in the subway—rats, cockroaches, pigeons, opossums—would be the first ones to take advantage of the human-free passages. 

Within the first month, the manicured lawns of Central and Prospect Park would grow wild and unkept. “When you stop mowing a lawn, you get a meadow,” says botanist Peter Del Tredici, a senior research scientist emeritus at the Arnold Arboretum of Harvard University, who wrote a book on urban plant life. Within a month, dandelions, ragweed, and yellow nutsedge would start popping up in the now knee-high grasses of New York’s iconic parks. “First, it’s herbaceous plants, but then, you know, you get trees and shrubs and vines,” says Tredici. 

From Year 1 to Year 10: Decay Sets In 
In a year without people, many of New York’s buildings would start to deteriorate. “The glass facades would be the first to go,” says Horvat. The single-pane glass on brownstones and family homes would be the most vulnerable, but in a decade, even the heat-strengthened glass on skyscrapers would start to wear down and crack. And once windows break, water gets in. “Then you’ll have plants start growing in there,” says Tredici. Apartments would transform into humid hothouses, the perfect habitat for mosquitoes, water snakes, fungus, and rushes. “It’s like a wetland on the second floor.”...

....MUCH MORE 

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