21st-century storms are overwhelming 20th-century cities

On Wednesday night, New York City received between 6-10 inches of rain in a matter of hours. This is more than the amount that fell on San Jose, California over the past year. Water rose through basements and leaked through roofs. Rainwater poured into subway stations, where it pooled on tracks. Floods were caused by Hurricane Ida's remnants, which had battered the Gulf Coast earlier this week. The death toll in the region had reached 40 as of Thursday evening. Subway delays and suspensions persist.
You can see that the city's infrastructure was built in late 19th century and early twentieth centuries to withstand storms that come every five to ten years. Record-breaking storms are now a regular occurrence. The scene of daily commutes was transformed by Ida, a reminder that climate change is upon us all. Zeke Hausfather is a climate scientist who is also the director of climate energy at Breakthrough Institute. He says that wildfire thunderclouds can be seen in the West and in Texas. It's a bit crazy to imagine it all happening simultaneously.

The storm washed away roads. It also flooded the alternatives to getting out of your car: sidewalks, bike lanes and public transit systems. All that was left of New York City on Thursday was submerged. Images of water gushing into subway stations brought home the reality of the crisis. Michael Horodniceanu, ex-president of the Metropolitan Transportation Authoritys Capital Construction Company, and chair of the Institute of Construction Innovations, at NYU, said that you don't have to be an expert on infrastructure to see that this is a problem. We are beginning to see the effects of what I consider a lack of attention to our infrastructure.


Nine years ago, Hurricane Sandy caused New York's first climate-related wakeup call. It flooded low-lying areas, and yes, even subway stations. According to the Mayor's Office of Resiliency, nearly $20 million has been spent on climate-proofing New York City since then. Some of the funding was used to solve a different problem than that presented by Ida, water from rivers. All the water from the rivers fell from the sky this week, threatening areas higher than sea level.

Because of a climate quirk, Idas's remnants dumped all that water in the Northeast. While you might expect less rain on a warmer planet, some areas of the world (including the US Northeast) are experiencing an increase in heavy rainfall. Hausfather says that temperature directly influences how much moisture an atmosphere can hold before it rains. Hotter air retains more moisture, while cooler air retains less.

Heat is the key to a hurricane: Ida grew quickly due to abnormally warm Gulf of Mexico waters. This accelerated it just before landing, creating 150-mile per hour winds. Ida, a swirling mass warm air, held on to a lot of moisture. Even though it was pushed inland by the wind, Ida still retained a lot of moisture.

Although Hurricane Ida was not caused by climate change, scientists now know that it is making hurricanes worse. Hausfather says it is one of the most fundamental physical relationships in the climate. For every degree [Celsius] that the atmosphere is heated, there are about 7 percent more water molecules in the air. This means you can experience much greater rainfall events. The warming of the gulf has caused hurricanes to become more intense in recent decades.

This was possible 100 years ago when New York City's bones were put together. Engineers imagine the worst storms that could be drained by a sewer system. This storm may not happen more than once every 10 to 20 years. New York's sewer system is built for a one-in-five year storm. Although scientists still have to calculate the exact number of people who were affected by the storm that flooded New York, it is clear that this was not a one-in five chance. This metric would take hundreds of years.


Another problem was the nature of Wednesday's storm. According to David Farnham (an environmental engineer at Carnegie Institution for Science), intense rainfall can often be caused by small cells moving across a city. Farnham has studied New York's sewer system. It may rain everywhere, but it is intense in a small area.

In Maplewood, New Jersey 8.39 inches of rain fell in the time period from Wednesday night to Thursday morning. Millburn, located just three miles away, received about half the amount of rain, at 4.4 inches. Even so, the downtown was still muddy and full puddles by morning.

After years of improvements, 60% of New York City now has a combined sewer system. This uses one pipe to transport both stormwater and wastewater to treatment plants. The system can quickly become overwhelmed by heavy rainstorms. Detritus from city livingtrash, plants and other gunkclogs can also block the drains, further complicating the situation. Farnham says that a kahuna this large won't drain it fast enough to prevent flooding.

It has been working to separate the combined sewer systems and clear clogged drains when there are storms. It has removed or raised subway grates in some cases. These were originally built to allow fresh air flow into underground spaces, but now appear like holes that let water in. The MTA has constructed flood-proof doors that can be closed if the water is too close in some areas.

New York City, for example, can build more green infrastructure to address their water problems. This means less asphalt and more dirt. For example, you might create green spaces along roadsides so water can percolate and flow into stormwater drains. This will remove pollution and trash. Los Angeles has been doing it for rainwater capture. Horodniceanu says this is a long-term project. Retrofitting cities in order to address what's coming and what's already here will require a lot of scarce resources: more funding.

This story first appeared on wired.com