Sponge city

“When it rains, it pours” once was a metaphor for bad things happening in clusters. Now it’s becoming a statement of fact about rainfall in a changing climate. Across the continental U.S., intense single-day precipitation events are growing more frequent, fueled by warming air that can hold increasing levels of moisture. Most recently, areas north of Houston received 12 to 20 inches (30 to 50 centimeters) of rain in several days in early May 2024, leading to swamped roads and evacuations. Earlier in the year, San Diego received 2.72 inches (7 centimeters) of rain on Jan. 22 that damaged nearly 600 homes and displaced about 1,200 people. Two weeks later, an atmospheric river dumped 5 to 10 inches (12 to 25 centimeters) of rain on Los Angeles, causing widespread mudslides and leaving more than a million people without power. Events like these have sparked interest in so-called sponge cities – a comprehensive approach to urban flood mitigation that uses i...