This story was originally published by WIRED and is reproduced here as part of the Climate desk cooperation.
Earlier this month, the future fell on Los Angeles. A long band of moisture in the sky, known as an atmospheric river, poured down 9 inches of rain on the city over three days – more than half of what the city typically gets in a year. This is the kind of extreme rainfall that will become increasingly extreme as the planet warms.
However, the city’s water managers were ready and waiting. Like other urban areas around the world, LA has in recent years turned into a “sponge city,” replace impermeable surfaces, such as concrete, with permeable surfaces, such as dirt and plants. It also developed “dispersal grounds” where water accumulates and seeps into the earth.
With traditional dams and all that newfangled sponge-like infrastructure, the metropolis collected 8.6 billion liters of stormwater between February 4 and 7, enough to supply 106,000 households with water for a year. For the rainy season in total, LA accumulated 14.7 billion gallons.
Long dependent on snowmelt and river water brought in from far away, LA is on a quest to produce as much water as possible locally. “There’s going to be a lot more rain and a lot less snow, which is going to change the way we capture snowmelt and the aqueduct water,” said Art Castro, manager of watershed management at the Los Angeles Department of Water and Power. “Dams and distribution grounds are the workhorses of local stormwater harvesting for either flood protection or water supply.”
Centuries of urban planning dogma dictate the use of gutters, sewers and other infrastructure to funnel rainwater out of a metropolis as quickly as possible to prevent flooding. Given the increasingly catastrophic urban flooding seen around the world, but it clearly doesn’t work anymore, so now planners are finding clever ways capture stormwater and treat it as an asset instead of a burden. “The problem of urban hydrology is caused by a thousand small cuts,” says Michael Kiparsky, director of the Wheeler Water Institute at UC Berkeley. “No ramp or roof by itself causes massive alteration of the hydrological cycle. But combine millions of them in one area and it does. Maybe we can solve that problem with a thousand Band-Aids.”
Or in this case, sponges. The trick to making a city more absorbent is to add more gardens and other green spaces that allow water to seep into underlying aquifers – porous underground materials that can hold water – from which a city can then draw in times of need . Engineers are also greening medians and road areas to soak up the water that would normally rush off the streets, into sewers and eventually to the ocean.
As the American West and other regions dry out, they are looking for ways to produce more water themselves, instead of importing it by aqueduct. (That strategy includes, by the way, the recycling of toilet water into drinking water so cities reduce water use in the first place.) At the same time, climate change is fueling rainstorms, counterintuitively enough: For every 1 degree Celsius of warming, the atmosphere can hold 6 to 7 percent more water, meaning there’s often more moisture available for a storm to dump as rain. Indeed, studies have found that the West Coast’s atmospheric rivers, like the one that just hit LA, get wetter.
To exploit all that free water falling from the sky, the LADWP carved out large patches of brown in the concrete jungle. Stormwater is fed into these distribution grounds and collected in cesspools. It allows it slowly seep into the underlying aquiferwhich acts as a kind of natural underground tank that can hold 28 billion liters of water.
During a storm, the city is also busy collecting water in dams, from which it diverts into the distribution areas. “After the storm is over, and it’s a bright sunny day, you’ll still see water being released into a channel and diverted to the distribution areas,” says Castro. In this way, water moves from a reservoir where it is exposed to sunlight and evaporation, to an aquifer where it is safely banked underground.
On a smaller scale, LADWP has experimented with turning parks into mini-dispersal lots, diverting stormwater there to drain into underground cisterns or chambers. It also deploys green spaces along roads, which have the added benefit of mitigating flooding in a neighborhood: The less concrete and the more dirt and plants, the more the built environment can soak up stormwater as the real environment does naturally.
As an added benefit, the deployment of more of these green spaces, along with urban gardens, improve the mental health of residents. Plants here “sweat”, cool the area and knock the back urban heat island effect — the tendency of concrete to absorb solar energy and release it slowly at night. By reducing the summer temperatures, you can improve the physical health of residents. “The more trees, the more shade, the less heat island effect,” says Castro. “Sometimes when it’s 90 degrees in the middle of summer, it can get up to 110 degrees under a bus stop.”
LA is far from alone in getting spongy. Pittsburgh is also rolling out more rain gardens, and where they absolutely must have a hard surface — sidewalks, parking lots, etc. – they use special concrete bricks that allow water to seep through. And a growing number of municipalities are investigating properties and charge owner fees if they have excessive impervious surfaces such as pavement, which the switch to permeable surfaces such as plots of native plants or urban gardens for producing more food locally.
So the old way of stormwater management is not only increasingly dangerous and ineffective as the planet warms and storms become more intense – it stands in the way of a more beautiful, less sweltering, more sustainable urban landscape. LA, of all places, is showing the world there is a better way.
