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San Diego Should be a “Sponge City” to Soak up Climate Crisis Floodwater – Watts Up With That?

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Essay by Eric Worrall

Professor Franco Montalto of Drexel University wants to slow runoff and allow parts of the city to flood, to mitigate damage from extreme rainfall and reduce runoff pollution.

As climate change amplifies urban flooding, here’s how communities can become ‘sponge cities’

Published: May 8, 2024 4.03am AEST

Franco Montalto
Professor of Civil, Architectural and Environmental Engineering and Director, Sustainable Water Resource Engineering Laboratory, Drexel University

“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 innovative landscape and drainage designs to reduce and slow down runoff, while allowing certain parts of the city to flood safely during extreme weather. Sponge city techniques differ from other stormwater management approaches because they are scaled to much larger storms and need to be applied across nearly all urban surfaces.

Read more:

Model based claims that flooding is getting worse on a global scale are not backed by observational evidence.

As for the “sponge city” plan, this all sounds fancy and modern, but what about putting peoples homes first, and just building bigger drains?

In my subtropical town on the East Coast of Australia, we have street drains you can comfortably walk along. The kinds of rain which causes major flooding in San Diego, we call that “Wet Season”.

It takes weeks of heavy tropical deluge to even begin to flood those suspiciously flat areas in my town which nobody should ever have built on. Where I live on a slightly elevated location, it would take a direct hit from a tropical cyclone to do real damage. My home is very rarely threatened by floods, even when my street turns into a river – all the runoff water gushes harmlessly into our oversize drainage system, and within 20 minutes of the rain stopping all the surface water is gone.

I’m not denying runoff management plays a role, slowing water entry into river systems can reduce peak flood. But sometimes you just have to move the water very quickly to somewhere else.

In the article above Professor Franco Montalo emphasised the benefits of greener water management systems, such as reduced pollution wherever you are dumping the runoff. But if homes are threatened, who cares about a little pollution? Keeping people’s homes safe from floods should be the highest priority.

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