Editor’s Note: This is the first in a four-part series that examines the complex relationship between green spaces, public policy and the urban heat island effect, while highlighting citizen-led strategies to mitigate the sweltering heat. This series, which reflects the author’s point of view, was originally conceived for Broken Sidewalk, an urban design blog founded by the late Branden Klayko, but has been revised and updated for Insider Louisville.
On July 5, Louisville’s heat index rose to 108 degrees, giving the city the distinction of having the highest heat index in the nation that day.
This year, the city had the hottest May in recorded history. But that’s not all: Louisville has had two of the warmest consecutive spring and winter seasons over the last two years. This is largely the result of the urban heat island effect (UHI) — a human-made problem.
An overabundance of concrete, a lack of healthy vegetation, and the unrestrained use of overhead power lines are partly to blame. Consider as well, the city has a transportation network designed for motor vehicles that produce excess heat and pollution, which are huge contributors to the UHI effect.
If the city’s dwindling tree canopy (and the milquetoast tree ordinance that Metro Council recently adopted) is any indication, recent studies show we are woefully unprepared for a future that is guaranteed to be hotter than we could imagine.
Make way for the almighty automobile
In April 2016, the Urban Climate Lab at the Georgia Institute of Technology released their study on Louisville’s urban heat island to the public. The reveal was sobering: temperatures have been escalating at a rate that’s almost twice as fast as Phoenix, putting Louisville on track to being one of the “fastest-warming cities in the country,” according to one of the co-authors of the study Brian Stone.
The trend is largely attributed to the widespread use of impervious pavement in streets, highways and surface parking lots in Louisville’s core neighborhoods. According to the U.S. Environmental Protection Agency, such surfaces can absorb solar heat at levels 50 to 90 degrees Fahrenheit hotter than the air.
This is why it’s referred to as an “island” — because the heat remains trapped within the center of the city that contains the most concrete, surrounded by an “ocean” of mild air rising from shaded porous surfaces more commonly found in affluent exurbs.
It’s a challenge that exists in many cities, not just Louisville. Anywhere there’s a densely populated area with high levels of energy consumption, there’s the likelihood for lingering urban heat.
As demand for cooling increases during peak temperatures (by around 2 percent for every one degree Fahrenheit rise, according to some estimates), it creates a negative cascading effect for city dwellers. When air-conditioners and refrigerators are turned on full blast, it necessitates additional power from nearby coal-fired plants. This generates more pollution and heat for the region, thereby inducing more demand for electricity. And so on, the cycle continues.
At every step in this process, excess heat is dispersed into the surrounding environment. This is known as waste heat, and it contributes to about one-third of total urban heat produced.
Factories, power plants, and gas-powered vehicles emit two particularly destructive elements into the atmosphere: nitrogen (NOx) and volatile organic compounds (VOC). When exposed to high heat and a stagnant atmosphere, these emissions can create ground-level ozone — a chemical reaction that produces hotter surface-level temperatures.
Consider Interstate 65, which cuts directly through downtown. All those cars, semi-trucks and out-of-town vehicles that are simply “passing through” are actually spewing toxins that make people sick and magnify the UHI effect. Eventually, some of those traveling vehicles will need parking spaces. So, block-by-block, this artificially induced demand for parking has eroded our streetscape and allowed our once-dense urban districts to become “parking craters.”
Transforming parking policies, growing green space
For evidence, look no further than the “SoBro” neighborhood, which spans from Ninth and Second streets, directly south of Broadway. This is an area of town that seems to be in a near-constant state of demolition and has become what Branden Klayko called a “dead zone separating the two ends of town.” It serves as a lesson on the overwhelmingly negative impacts of parking minimum laws that mandate parking lots for new commercial developments.
Such regulations are widely understood to be archaic, benefiting only big box stores at the expense of local businesses and historic preservation. The only bright spot is that Louisville’s parking requirements are exempt in the Central Business District. However, this exemption doesn’t apply to adjacent communities like Limerick, Russell or Smoketown — areas that were repeatedly torn down and replaced with heat-absorbing highways and parking lots.
If you’ll notice, many of these civic ailments stem from land use policies that have served the demands of the almighty automobile. Indeed, Louisville has transformed from being a city built around the human scale to a combined county-city metropolitan area teeming with sprawl. Thus begot the suburban strip malls, restaurant chains and other car-centric developments that demand a sea of parking and multilane roads to connect them all together.
It’s not all bad news. If Louisville can find a way to eliminate outdated parking minimums, the empty blocks in the center of the city could be rebuilt once again. But it won’t be easy.
Neighborhoods that have demolished their older, usually more affordable, housing stock will inevitably suffer because it loses existing residents that could have otherwise laid the framework for revitalization. There’s also the tangible loss of historic structures, which carried the potential to anchor new development.
Streetsblog USA has an excellent primer for planners interested in re-stitching the urban fabric of their cities. One strategy includes constructing “liner buildings” along the outer perimeter of vacant blocks, thereby transforming parking lots into semi-enclosed, pedestrian-friendly plazas.
Researchers from the Urban Climate Lab made some suggestions for Louisville, including the use of more reflective and permeable surfaces on roadways. Doing such would help repel solar radiation and mitigate stormwater overflows, making it easier on both our air and sewers. Other cities have already started using such methods to tackle their own heat island issues.
Last year, residents in Los Angeles experimented with this by applying a special reflective gray paint known as CoolSeal over a few parking lots. They discovered that surface areas covered in CoolSeal were 10 degrees cooler than the area that was covered in traditional asphalt. No doubt such an inexpensive project could easily be implemented in one of the dozens of surface parking lots in downtown Louisville.
It also couldn’t hurt to have a few more green spaces around town, like playgrounds, parks and gardens. What’s great is that these green spaces can be modified to fit almost any urban surface: old industry yards, rooftops and even decommissioned railways (think of the High Line in Manhattan).
Even small patches of grass between buildings and sidewalks could qualify as “green space.” When designed with intentionality, such parcels could take the form of neckdowns, bioswales, and other low-lying plant beds. These help lower ambient air temperatures through evapotranspiration — the combined process of evaporation and transpiration by which solar energy is converted into water vapor.
Green spaces also provide an opportunity for residents to connect with one another and become more self-sufficient. According to a research study published in the Journal of Community Health, families with access to public gardens have seen demonstrable improvements in food security, community relationships and dietary intake, all of this while simultaneously enhancing the vitality of native wildlife and boosting the regional bee population.
An influx of green, reflective and porous surfaces would be a good thing. However, the UHI study concluded that the most effective way to beat the heat was to expand and protect our tree canopy, which has seen a seven percent decrease, or about 54,000 trees, per year since 2004.
Metro officials have taken baby steps by updating the city’s existing tree ordinance. But it’s not nearly as comprehensive as it could be. It also doesn’t address the existing disparities in the current right of way system regarding public trees and utility easements.