Can Sponge Cities Save Us from the Coming Floods?
This time, the sound of pouring rain told him that trouble was coming. “The kids were doing our afternoon activities,” she said, “and they were like, ‘Oh, the water is coming up through the door!’ » A colleague called: water was rising in Goodwin’s car in front. When she opened the door to the daycare, she remembers, “the water rushed in in torrents. The children were screaming and screaming.”
She and a colleague carried the children onto tables. Stormwater, Goodwin pointed out, picks up “everything that’s on the street”: gasoline, heavy metals, raw sewage, rodents. As the fetid mixture reached knee level, she called 911. Firefighters arrived and helped daycare staff carry the children over a fence and to an upper floor. Everyone escaped safely.
A few blocks away, at Kingston Avenue and Rutland Road, thirty-nine-year-old Aaron Akaberi was in a basement apartment with his two dogs when the water started rushing in. He carried one dog to higher ground and returned for the other. But the flood must have moved faster and with more force than expected. Within seconds, Akaberi and his pet were fighting for air. Both drowned. Their bodies were only found after the fire department’s rescue dive team brought in a pump.
A flood sensor at the intersection recorded 22.4 inches of water at street level between 3:01 a.m. and 3:26 a.m. PM; the underground spaces took several extra feet. The downpour surprised almost everyone, but the day’s precipitation total was as predicted: about two inches. Flooding depends less on the amount of rain and more on the speed at which it falls. Two inches a day is one thing. Two inches in thirty minutes can overwhelm drainage systems and leave deep ponds in lower areas as the water goes down.
“By our calculations, this was a one in five to ten years event,” Radell told me, using a metric that, because it relies on past models, becomes less and less useful as climate change challenges those models. Events like this are beginning to seem ordinary – recurring evidence of the mismatch between aging infrastructure and an emerging ecological reality. That’s why a new generation of designers is reinventing flood control, starting from a counterintuitive principle: the safest city is one that can accommodate water.
There is a formula behind flooding. The Clausius-Clapeyron equation, introduced almost two centuries ago, describes the relationship between air temperature and atmospheric pressure. Warmer air holds more water, and the relationship is exponential, so small increases in temperature can lead to huge increases in precipitation intensity. For years, climatologists have said that warming would lead to heavier downpours. Today, it seems that future has arrived.
In recent years, cities have experienced short storms that turn subway stations into lakes, streets into rivers and cars into boats. Zhengzhou, China, received nearly eight inches of rain per hour on July 20, 2021. In the Libyan towns of Derna and Bayda, no monitors measured hourly rates on September 10 and 11, 2023, but totals suggest a storm of terrifying force: more than sixteen inches in twenty-four hours, followed by two dam collapses and more than eleven thousand deaths. The Valencia region of Spain gained worldwide attention on October 29, 2024, when nearly seven inches fell in an hour. Elsewhere, record twenty-four-hour totals, including in São Paulo, Dubai and Milwaukee, underscored the new reality.
No city was designed for this kind of weather. Modern sewers came into existence in the 19th century, usually after disasters caused cities to upgrade their civil infrastructure. Hamburg was rebuilt after the fire of 1842, London after summers like the so-called Great Stench of 1858. Engineers replaced streams and marshes with gravity-fed pipes that carried sewage and rainwater to rivers and seas. These “combined systems” relied on rain to flush the network and were built for ordinary storms. When the heavens really opened, they stepped back.
