Parking lots can be a double problem for cities: they absorb and hold heat, and their impervious surfaces also block rain from soaking into the ground. With climate change worsening both hot weather and intense storms, cities and other groups are experimenting with ways to change how parking lots are built—seeking surfaces that stay cooler and manage stormwater before it becomes polluted runoff.
One example is at the Hampton Roads Planning District Commission headquarters in Virginia, where staff said a damaged asphalt parking lot needed repair. Instead of replacing the lot with more dark blacktop, the commission opted for a mix that includes porous concrete panels along with areas with native plants and recycled materials. The project was completed last year, according to the Associated Press.
Jill Sunderland, the commission’s senior water resources planner, said the porous-concrete design changes what happens during rainfall. “the rain infiltrates faster than it can puddle and stop on the surface,” Sunderland said. She also said the difference shows up to visitors on hot days, adding, “You notice too, that it’s cooler,” and “You really can tell a difference out there … not to mention it’s just more inviting.”
Across the U.S., similar efforts are spreading, the AP reported, as planners look for interventions that address multiple issues at once. The report cited cities that have required or promoted permeable paving where practical, including New Orleans, which required its Department of Public Works to use permeable paving in parking lots and other spaces where feasible. In Indianapolis, the Newfields art museum transformed parking areas with bioretention rain gardens and with a permeable grid instead of traditional blacktop, while Denver’s “dePaving a Greener Denver” initiative is looking to reduce the city’s coverage of parking lots and other impervious surfaces.
Some approaches focus first on cooling. In some downtown areas, parking can take up a quarter or more of the land, and a UCLA professor, Adam Millard-Ball, said studies show that more than a third of parking spaces can sit empty at any given time. Because many lots sit idle part of the day, the Associated Press said some entities use grants to replace or transform asphalt. Los Angeles’ Pacoima neighborhood, for instance, has used reflective coatings meant to keep the ground from absorbing as much heat.
Vegetation and shading are another line of attack, with the AP describing requirements and policies that increase tree cover over parking lots. Sacramento, California, requires developers to plant enough trees to shade half of a lot within 15 years, while Washington, D.C., and Seattle have green area requirements for landscaping on new development. The report also described how darker paved surfaces can trap heat and drive temperatures up, contributing to an urban heat island effect—an outcome attributed by the AP to Vincent Cotrone, an extension educator of urban forestry at Pennsylvania State University.
Other alternatives target stormwater runoff and water quality by letting water pass through or be filtered. When rainwater runs off impervious pavement, it can carry pollutants such as oil and heavy metals into waterways, Cotrone said. The AP described runoff-control methods that include lattice and interlocking pavers that allow rain to filter through, plus permeable materials such as stone beds, brick pavers and honeycomb-style structures.
The Hampton Roads project also includes a transition detail designed to keep runoff from moving sediment between surface types. The AP said the commission uses a stamped, grooved concrete border so that when stormwater runoff flows from traditional concrete to porous concrete, sediment gets trapped instead of clogging up and requiring maintenance. Long planted channels called bioswales and recessed rain gardens also rely on sand, soil and plants to filter pollutants before stormwater reaches streams or sewers.
At Newfields in Indianapolis, the AP described one parking lot featuring rain gardens and an overflow lot made of recycled plastic grid pavers. Jonathan Wright, the director of the garden, said the choice reflected how the space gets used, telling reporters, “It has worked really well for us because we don’t park on that lot every single day.” He added, “Why should it be asphalt and not breathing and not permeable when you only need to use it 10% of the time?”
Cost and durability remain major considerations in decisions about whether to switch from asphalt. Sunderland said the porous-concrete approach may cost more at the start, but she argued it offers more useful life. “If we were going to just repave it with asphalt, we could have done it significantly cheaper,” Sunderland said, adding, “It’s more expensive initially, but you get so much more life out of it.”
Industry representatives, however, urged caution about longevity and maintenance. Buzz Powell, technical director at the Asphalt Pavement Alliance, a coalition of national industry groups, said asphalt is versatile and designed for heavy traffic. Powell also said it is important to examine lifecycle impacts and warned that some alternatives may not handle heavy stresses. “I just think we need to be really, really careful when we put alternative systems in to make sure that we have a good understanding of what the life cycle impact is gonna be,” Powell said. He added, “Some things can be really sexy on the front end and look good on paper, but then when you run a trash truck over it, it can’t handle the stresses and strains.”
Other experts cited barriers tied to budgets, saying cities may struggle to find funding to retrofit older lots. Cotrone said many parking lots remain unchanged even as they heat up, arguing that some cities don’t have the dollars to retrofit those areas. At the same time, the Associated Press said that changing parking surfaces and policies—such as reducing parking-space minimum requirements—can help address multiple challenges, including heat, water runoff and broader equity concerns.
The AP also quoted Greg Kats, founder of the Smart Surfaces Coalition, saying that a single city’s changes may not create broad impact on its own. “The reality is, one city changing their surfaces is just not by itself not going to have a big impact,” Kats said. He said the benefits become more meaningful when cities can understand the scale of advantages in a rigorous way.
In the end, the report portrayed the shift away from traditional blacktop not as a single solution, but as a set of design and policy choices—each aimed at different parts of the heat-and-runoff problem, and each requiring planners to weigh upfront costs, lifecycle performance and what their communities can sustain over time.