Cooling goo sidewalks and other strange new weapons in the war on urban heat
Los Angeles can sometimes feel like a sprawling hellscape of heat: in the northern valleys and the southern city, metal playground equipment, car steering wheels, even the ground itself effectively become weaponized.
The more than 300 days of sunshine a year that for generations have made LA such an attractive place to live and visit are becoming a grave liability due to the climate crisis.
The city gets so murderously hot all year-round, its residents routinely suffer heat-related death even in winter. Last summer, city residents in endured some of its highest temperatures ever recorded.
Worse is likely to come.
LA’s hot inland areas are projected to experience twice as many extreme heat days by mid-century; University of Maryland researchers project, on current emissions, that by 2080 the climate will be as hot as Baja California, Mexico, is now.
That heat is not equitably distributed across the city’s geography, or its income brackets: inland suburbs regularly reach over 100F (38C) while the beach is 78F (25.5C) and breezy; wealthier neighborhoods enjoy shade-dappled walkways and abundant air conditioning, while poorer ones are largely exposed to the heat, both outside and inside.
“There can be a 25F (14C) difference in just four to five miles as the crow flies, and a very different temperature future,” said Jonathan Parfrey, executive director of nonprofit advocacy and coalition-building group Climate Resolve. “There has to be a variety of different strategies to help people cool down.”
Los Angeles is embracing those strategies, in the vanguard of cities innovating to mitigate the damage of rising temperatures. But the challenges are substantial.
Mayor Eric Garcetti has pledged to reduce the city’s temperature by 3F (1.6C) by 2050, as part of his updated climate adaptation plan. That will mean wrenching LA off its current heated trajectory, with temperatures in the region on pace to rise 3-5F (1.6-2.7C) by then.
It’s not just heat
For Los Angeles, the changing climate means droughts will last longer and become more extreme, helping to fuel longer and more devastating wildfire seasons. Climate crisis will further diminish the already-taxed water stores upon which LA relies. At the same time, researchers expect more extreme “atmospheric rivers” – storms so massive they’re essentially waterways in the sky – that will infrequently, but decidedly, douse and overwhelm the city.
Los Angeles must reconsider and reconstruct its infrastructure. The Environmental Protection Agency recommends a multi-pronged, green infrastructure approach to combat the “urban heat island” effect, in which cities feel hotter than their greener, less populated surroundings. Some of that is now underway.
The mayor’s climate adaptation plan includes a goal of increasing the total land area covered by cool surfaces by 10% by 2025, and 30% by 2045. Research from the Los Angeles Urban Cooling Collaborative found that infusing cooling measures in the built environment, from tree canopy to cool roofs to reflective streets, could reduce heatrelated deaths in the city by 25%.
“Health, transportation, buildings, social equity and justice – all manner of different expertise needs to be deployed to do this in the most effective way possible,” said Kurt Shickman, executive director of the Global Cool Cities Alliance.“LA is one of the few cities that’s embraced the idea of being a test bed for all this stuff.”
Cool surfacing
Few city projects have inspired as much apparent excitement as the pools of titanium dioxide-infused goo that Los Angeles has been spreading on its asphalt.
“When we’re applying it, people come out and ask what we’re doing,” said Greg Spotts, assistant director of the Bureau of Street Services.
In a first-of-its-kind initiative, the LA Bureau of Street Services is hoping the reflective Cool Seal coating will reduce extreme heat in some of the city’s hottest neighborhoods. “Separate from the discussion about global warming, Angelenos’ experience is that their neighborhoods are getting hotter,” said Spotts.
A one-quarter millimeter layer of Cool Seal costs about $0.60 per square foot, and can reduce surface street temperature by roughly 10F (5.5C). Spotts demonstrated the difference to the Guardian using a handheld infrared thermometer gun on a 98F (37C) day.
“We’ve noticed that even dogs and cats actually prefer to walk on the cool pavement coating,” said Spotts. They’ll cross the street just to get to the cool stuff.
In 2019, the agency expanded the experiment from single city blocks distributed across the region, to coating several blocks at a time in neighborhoods determined to be particularly vulnerable to urban heat based on local climate, lack of shade and economic disadvantages.
“Originally, we thought this was about reducing air conditioning usage and the associated carbon emissions. But it’s really becoming more about public health,” said Spotts.
Before cool streets, LA was the first city in the country to require cool roofs on new and renovated construction in order to reduce indoor temperatures without the use of air conditioning. The roofs worked so well, why not tackle the roads next?
Streets make up about 15% of the city’s land, while parks comprise 13%. If heat-trapping, car-centric roads are one of LA’s biggest climate problems, they’re also a potential site of intervention.
But the research on cool street cover leaves some open questions. According to a 2017 study, most cool pavement sealants were more resourceintensive than ordinary paving material. There’s also concern that staining on white roads could counteract their benefits. Alternatively, if they stay fresh and bright, some fear they could actually reflect the hot sun back at unsuspecting residents.
Still, Spotts is undeterred. “The street is made of the same stuff it’s been made of since World War II,” said Spotts. “We think it’s time for cities and suppliers to experiment.”
Water
Permeable pavement is a far more subtle addition to LA’s climate resiliency schemes than cooling landcover. Unlike a gleaming white-coated street, the porous pavement and bioswales that catch and filter runoff don’t look like anything special. The dry wells that capture that water for reuse blend entirely into the urban landscape.
On a tour of water-capturing green infrastructure, Kevin Ho, an LA city sanitation engineer, pointed to two metal covers set into the road, several feet in front of a massive storm drain. “When it rains, it’s like opening up a fire hydrant and pointing it down into the dry well – it just collects it all,” said Ho. “If possible, we would just put dry wells throughout the city.”
In a partnership between the City Department of Water and Power, the Bureau of Sanitation and California State Coastal Conservancy, these experimental projects have been distributed across a handful of major thoroughfares and small residential side streets, with the goal of increasing local water security and reducing local heat.
The mayor’s resilience plan calls for water infrastructure that “will ensure the city is prepared to handle both extreme wet and extreme dry years”. Right now, LA county gets 41% of its water from local underground aquifers and recycling – the goal is 50% by 2025. Permeable pavement, bioswales and dry wells can make the city better adapted to arid periods, and make flood-prone neighborhoods more resilient to superstorms.
The distributed stormwater capture project in the San Fernando Valley stands to collect enough water to serve around 1,200 families per year. It’s a literal drop in the bucket, but the initiative is still in an early stage.
“These projects are so spotty, and they’re at all different levels of green,” said Kara Kemmler, a coastal conservancy project manager.
“I would love to see some more trees,” lamented Kemmler. “So you have that water capture, but create some shade, some carbon sequestration, some urban heat island mitigation while you have the opportunity. ”
Shade
Creamy asphalt sealant lowers the surface temperature of a road roughly 10F. But the shade from a mature, leafy tree can provide more like 40-50F (22-28C) of cooling power, on top of sequesteringcarbon.
“By and large the literature is kind of mixed on which one is ‘better’ – I’m a firm believer that we’ve got to do both,” said Edith de Guzman, executive director of the nonprofit Tree People.
Trees seem to be the obvious adaptation fix to cool a city, recapture water runoff and increase local carbon capture. Earlier this month, the mayor’s office appointed LA’s first forest officer to oversee increasing the city’s canopy by at least 50% by 2028 in areas that currently have the least shade.
“There’s all manner of state or other funding sources that will allow for tree planting to occur. But this is an asset that needs to be maintained,” said de Guzman.
Instead of unilaterally taking on the project of greening LA, Tree People trains those who want to green their own neighborhoods, thus creating a network of tree-passionate planters and waterers.
But compared to pouring reflective or permeable concrete, or installing a cool roof, planted greenery by its nature conflicts with the gray environment. Planting comes second to vehicle sightlines in the sprawling carcentric metropolis. And over time, the shallow roots on many of LA’s trees have torn up the pavement. The city recently settled a lawsuit that will require a $1.4bn investment in sidewalk, ramp and crosswalk repairs in order to make them disability-accessible.That settlement could provide an opportunity to green the city better by choosing more deep-rooted species.
LA appears committed to a greener, shadier future – but the city has fallen short in past efforts to create cool cover. Trees have gone unplanted. Bus shelters have gone unbuilt. The city is losing transit riders to car travel, and climate crisis could only make it worse.
A pilot at one large northwest valley transit station will create a variety of heat-beating infrastructure to make transit more attractive.
“If you knew you’d be completely in the shade, that there was water waiting for you at the train station, wouldn’t that be an easier place for people to take transit?” said Parfrey.
The future
Just as LA’s critical warming is not evenly distributed, neither are its heatrelieving elements. You can see this green gap in aerial photos of the city: Wealthier neighborhoods are shielded by foliage, while poorer ones are exposed to the sun – sometimes by design, in order to provide clear sight lines for surveillance cameras.
The gap in heat-beating infrastructure creates an inequitable distribution of health risk. While the city takes local wealth into account when determining where to install new heat-mitigating infrastructure, intracity inequality is not so easily paved over, from uninsulated buildings to higher proportional energy costs to longer waits at those unsheltered bus stops.
“If you want to look at a single issue that separates the haves from the have-nots, it’s heat,” said Shickman. “Every negative effect of heat hits low income neighborhoods and people of color more.”
Even for a city as apparently determined as Los Angeles, the investments and cultural change necessary to retrofit so much gray infrastructure are hard won. These projects are all still in a nascent stage. But every square inch of green infrastructure contributes to better adapting it to a hotter future.
“We’re aware of the projections out there and the reality that we are in for a fairly scary trajectory for continued heating. We are expecting more mortality, more illness,” said de Guzman. “But while we adapt we also have a recognition that there’s an inherently optimistic way that we can go about the situation that we’ve been handed.”
Climate advocates here see their role as two-fold: an urgency to green a gray LA and save lives, and to inspire greater climate action at the same time.
“Of course, urban heat island isn’t the same thing as climate change. But there’s something we can do in the interim, and we hope cooling down the city is a gateway to more activism and awareness,” said Parfrey. “Because this is a marathon.”
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We’ve noticed that even dogs and cats actually prefer to walk on the cool pavement coating Greg Spotts, assistant director of the Bureau of Street Services