Erica Peterson reports on environment and energy issues for WFPL, the National Public Radio affiliate in Louisville.

Maria Koetter squints into the sun and points toward the southeast, surveying Louisville from atop one of its tallest buildings.

“Look at that!” she says.


Sprawled before us are the elements that have shaped this city of 750,000. The Ohio River rolls muddy blue, straddled by bridges and dissected by barges that crawl through the watery thoroughfare that gave life to Louisville as a commercial center. Distant hills lush with fall foliage encircle the city, creating a basin that serves as Louisville’s foundation. Traffic rumbles in the distance on several of the major interstates that cross the city, and two coal-fired power plants belch out smoke in the horizon.

Closer in, a more stark landscape, largely stripped of nature, dominated by the man-made: The city center is marked by mid- and high-rise buildings and wide streets originally built for streetcars, but now functioning as six-lane arteries clogged with cars. Parking lots—dozens of privately-owned, half-empty parking lots—scar the city center. The occasional tree seems to pop out of the pavement and struggles to breathe.

“I think you could probably go to a tall building in many cities and see a boundary where you’re going from the dense urban core to a more residential area,” says Koetter, who is Louisville’s first director of sustainability. What Koetter is describing are the physical conditions that give rise to a phenomenon known as an urban heat island, where a city’s center experiences significantly hotter temperatures than its less-developed surroundings. Here’s how it works: During the hottest times of year, dark or paved areas—whether on roofs or on the ground—soak up and store heat. These surfaces continue to release this heat throughout the day and night, preventing the area from cooling down after sunset. Patchy urban tree canopies struggle to clean the air and keep temperatures down. The urban heat islands don’t cause air pollution, but make the effects of pollution worse.

Heat islands aren’t limited to southern or subtropical cities or places like Miami or Phoenix, known to have scorching summers. Denver, Portland, Ore., Minneapolis and Seattle are among the top ten cities in the nation with the most intense urban heat islands, according to a study released earlier this year by Climate Central, a nonprofit news organizations that reports on climate matters.

Brian Stone Jr. knows this phenomenon well. Stone is one of the country’s foremost experts in urban heat; he has made a career of literally taking the temperature of communities. “Cities essentially create their own climates,” he says. “And the urban heat island effect is one way to measure that. There’s a heat island effect, really, in every large city.”

But in few places is it felt more than in Louisville, sometimes to deadly effect.

Video: How America's Fastest Warming City is Going Green. | Photo by Mark Peterson/Redux

Stone’s research found that Louisville is warming at the fastest rate of any city in the nation, causing summer temperatures in the urban core to be up to 20 degrees higher than surrounding areas. And the gap continues to widen. On average, the disparity in temperatures between Louisville’s city center and outer areas has been growing at a rate of 1.67 degrees each decade—almost twice the rate of Phoenix, which is the second-fastest warming city.

For many Louisvillians, the effects are merely unpleasant or annoying. Residents crank up their air conditioners to battle the heat, raising their electricity bills. More coal is burned to keep up with peak demand, sending more pollution into the skies. As pollution and stagnant air bake in the sun, air quality worsens. The acres upon acres of paved surfaces in Louisville also exacerbate flooding issues and storm water runoff into the Ohio River. The storm water, warmed an extra 20 to 25 degrees by hot man-made surfaces, can cause significant disruptions of natural ecosystems.

But what has triggered Louisville’s urgency to solve its urban heat island problem is that people—especially the very young and very old and those with pre-existing health conditions—are dying.

Heat consistently kills more people in the United States than any other form of extreme weather, including hurricanes, earthquakes and tornados, combined; nationally, about 658 people die every year because of exposure to excessive heat, according to the Centers for Disease Control and Prevention. But that doesn’t take into account people who die of conditions like cardiovascular disease, which is exacerbated by the heat.

Open In New Window OPTICS: A Tree Grows in Louisville. (Click to view gallery.) | Mark Peterson/Redux

The problem is acute in Louisville. A 2012 study from the Natural Resources Defense Council estimates that 39 people die every year in Louisville from heat-related causes. That means that a city with .2 percent of the U.S. population experiences roughly 6 percent of heat-related deaths every year. The problem is only likely to get worse. Unless Louisville’s warming trend is reversed, the cumulative death toll could reach 18,000 by the end of this century—a projection that far exceeds that for any other city.

Louisville is taking this possibility seriously and, in the process, has been more aggressive and comprehensive than any other city in tackling the problem. Mayor Greg Fischer established a tree commission two years ago to reverse the city’s dramatic loss of tree cover due to storms, disease and development. The city doled out $115,000 earlier this year for a tree assessment, which, in Fischer’s words, will give Louisville a “street and address level” picture of the city’s tree canopy. Since 2011, the city has planted more than 12,000 trees, some of it in conjunction with individuals, corporations and non-profits that have sprung up to help in the cause. It also secured private grants to fund a $135,000 study of the city’s urban heat island. The analysis, which is scheduled to be done later this year, is the first of its kind in the country, and possibly the world, according to Stone, who is leading the project.



Louisville government has been active in other ways as well; two years ago, it hired its first director of sustainability (Koetter) and last year, its first urban forester. And it will soon offer incentives for commercial buildings to install plant-filled green roofs to help offset heat and control stormwater runoff.

“They’re one of the very few cities and city governments,” Stone says, “that has decided to really invest in this research and to pursue policies based on the outcome.”

It’s early days yet in Louisville’s battle against heat, but this much is clear: This Southern city in deep-red Kentucky, best known for bourbon and horse racing, is giving the crunchiest coastal communities a run for their environmental money.

***

On a recent Saturday, 150 volunteers fanned, planting trees in the city’s Shelby Park neighborhood, a working class area just off of downtown, full of single-family bungalows and shotgun homes. In the past year, the non-profit Louisville Grows has planted 600 trees—some canopy trees, such as maples; some apple, peach and pear species. On this day, they’re planting shade trees like redbuds and tulip poplars, 160 in all. About a third of the volunteers wear t-shirts identifying them as “citizen foresters.”

This is where Louisville’s present meets the future.

“It’s really important to us that while we’re planting the trees, we’re thinking in terms of a tree that’s going to be living for 100 years or much longer, and is going to carry on after we’re all gone,” says Louisville Grows Executive Director Valerie Magnuson.

American Forests, another non-profit, recommends that city centers are covered at least 15 percent by canopy trees. Louisville’s downtown only has an eight percent canopy, and Stone estimates the city’s overall tree canopy is in the mid-20 percent range. That’s far below other Southern cities, like Atlanta, where the canopy covers more than 50 percent of the city.

Ice storms and other extreme weather, as well as plant diseases and development are responsible for the downing of thousands of Louisville’s trees over the past decade. One pest alone—the emerald ash borer—has decimated the area’s 2.5 million ash trees, which represent 17 percent of the city’s tree canopy. Between one cause or another, Louisville lost 9 percent of its tree canopy between 2008 and 2012—or roughly 735 trees every year. Tree planting has become a priority as a way to begin to slow Louisville’s warming.

Click for more details about Louisville's tree canopy coverage. Canopy coverage data provided by Davey Resource group. Surface temperature data provided by Brian Stone, Georgia Institute of Technology. Graphic courtesy of the Louisville Courier-Journal .

Magnuson’s organization trained these citizen foresters in tree planting. They know not to plant taller species under power lines. They know how to dig the hole and compact the dirt. They know how to install the green “gator bags” around the tree, to ensure they’ll stay watered as their root systems develop.

The citizen foresters lead the rest of Magnuson’s volunteers, and also work to educate homeowners, who will be ultimately responsible for maintaining the trees.

“If they’re going to receive a free tree,” Magnuson says, “they’re taking on that responsibility to love the tree and make sure it’s mulched and watered.”

In the past several years, city government has been paying more attention to the tree problem, too.

“Part of the solution, yes, is planting trees,” says Erin Thompson, Louisville’s urban forester. “As any area, any city gets bigger and urban sprawl goes out, that means people develop and trees get cut down. Trees also hit a maturity maximum and then they decline downwards. They’re kind of like humans, they have a death. So, it’s very important to replace what you take away so you can retain the tree canopy that you have.”

“But then,” she adds, “another solution is managing what you do have.”

Until Thompson was hired, it wasn’t any city employee’s job to manage Louisville’s tree canopy as a whole. The city has always had an arborist, but his job exists on a more micro level—telling residents what trees they should or should not plant.

Erin Thompson, Louisville's urban forester, above. Below, a man who received a tree from the city because he wanted a little more nature in his yard. | Mark Peterson/Redux

Last year, the city’s tree budget included money just for planting trees. This year, Thompson successfully lobbied to have the budget also include money for maintaining the trees. Still, the city does not have a tree ordinance, as do other municipalities, mandating that a replacement must be planted for every tree that is felled or cut down, in part because developers have pushed back against being forced to spend the extra money to plant more trees. The city has said it may reconsider the need for an ordinance once its tree assessment is done.

Developers aren’t the only ones with concerns about Louisville’s new-found enthusiasm for greenery. Often, Thompson says people are excited to get free trees planted in their yards and in easements. But some residents are skittish, after seeing the destruction fallen limbs from larger trees have caused in the past.

“People have a mindset quite often of, ‘Oh, we’ve had all these horrible storms. Trees are a problem,’” Thompson says. “I actually don’t think that they are a problem. I think it’s something that you have to manage. Just like owning a house or a car. You don’t just buy it and assume it’s perfect. It’s always in a continual state of needing attention. Trees are the same way.”

Thompson works with homeowners to teach them how to maintain the trees planted in easements, which are technically city-owned property. But for people who are uninterested or unwilling, she’s been lobbying to promise maintenance, too. Now, Thompson’s tree plantings are maintained for three years by city contractors who water and prune them. After that, it’s the responsibility of the homeowner.

In front of a barber shop on South Shelby Street, one of Magnuson’s volunteer groups is digging a hole for a small maple tree. Three of them are third graders, members of a Cub Scout troop from Southern Indiana, just over the border.

Shelby Street is busy. And even on a mild day in November, it’s bright. There are few large trees in this stretch, and it’s easy to see how the sun’s rays would roast the neighborhood in the summer. Dirt flies all over as the boys energetically dig a hole for the tree’s root ball.

“Alex, please do not throw dirt on Connor’s mother,” Scoutmaster Lance Leach sighs. “That is not our goal.”

This is one of the many community service projects Leach’s scouts will complete this year. Many have an environmental focus: building nature trails, cleaning parks.

“Let me tell you what these trees are going to do in this neighborhood,” says Sarah Fosnight, a bartender at one of the city’s local breweries and a citizen forester who’s overseeing the scouts’ tree planting. “In the summer, when the sun beats down it heats up all these sidewalks and makes the neighborhood really, really hot. But if you have a shade tree, it will keep this area cooler, and it will actually help keep the entire city cooler.”

Urban Heat Islands 101.

The boys nod, and begin to wrestle the tree into the hole.

***

Trees may be a beautiful and natural way to combat deadly heat, but trees alone cannot reverse Louisville’s—or any city’s—urban heat island. The most significant contributors to the city’s increasing temperatures are man-made: the dark, paved roads, dozens of parking lots and heat-absorbing roofs. Local experts estimate conservatively that about one-third of Louisville’s downtown is dedicated to parking.

“The theory behind [cities] is that we ought to engage in this comprehensive planning, and we ought to regulate in sort of this systematic and consistent way,” says Tony Arnold, a law and urban planning professor at the University of Louisville. “And that’s a great theory, but in reality, almost anywhere, regardless of how great the plans are, there’s a lot of ad hoc decision-making.”

Realistically, city workers won’t be jackhammering out the black asphalt in privately-owned parking lots anytime soon and replacing them with parklands. The cost would be astronomical: Of the more than 6,600 parking spots in downtown surface lots, only 12 percent are owned by the city’s parking authority.

Still, Stone of Georgia Tech says there are ways to keep existing surface parking lots and cool them slightly. You can build islands with trees, for example. But the cheapest, easiest way would be to mandate a more reflective coating on the lots.

“That, over time, could greatly reduce the amount of heat that’s being absorbed and re-emitted in those areas,” Stone says.

That’s a theory that’s already been put into practice in other cities. In Chicago, the Green Alleys program is installing highly-reflective, permeable pavement in the city’s alleys that reduce urban temperatures and cut storm water runoff by up to 80 percent. In Austin, all new parking lots are required to have 50 percent canopy coverage within 15 years.

The most expedient way to lighten Louisville’s existing surface parking lots would be to resurface them with concrete, which is lighter-colored and more reflective than asphalt. The business opportunity hasn’t escaped the area’s concrete producers.

Volunteers with Louisville Grows plant seedlings. Since 2011, the city has planted more than 12,000 trees, some of it in cooperation with individuals and non-profits. | Mark Peterson/Redux

Brett Ruffing of the Kentucky Ready Mix Concrete Association says there are lots of benefits to using concrete, including the fact that the material can be up to 30 degrees cooler than asphalt. The trade group has paid for advertisements touting the durability and cooling properties of its product.

“Life is full of decisions. We can construct pavements that are cooler and could last 30 years or more. Why don’t we?” asks one radio ad broadcast around the city.

Price may be one answer. Concrete does, indeed, retain less heat than asphalt and can last 10 years longer, but it also costs an average of twice as much as asphalt—roughly $3 to $10 per square foot versus $1 to $5 per square foot.

Ruffing’s efforts have seen limited results. A major downtown bridge across the Ohio River is under construction, and Ruffing says his group was lobbying the city and the state’s transportation cabinet to surface it with concrete, rather than asphalt.

Louisville Grows Executive Director Valerie Magnuson re-mulches a tree planted recently by the organization. | Mark Peterson/Redux

“The downtown portion, the bridge will be concrete, but the pavement will be asphalt,” Ruffing says. “And I think there’s a few hundred football fields worth of asphalt pavement going down right there in downtown Louisville.”

The same idea of increasing the reflectivity of pavement also applies to roofs. According to the Environmental Protection Agency, a traditional black roof can be up to 90 degrees Fahrenheit warmer than the air temperature in the summer. A white roof will only be 30 to 40 degrees warmer than the air.

But the coolest roof of all is not dark or light, but green. These green roofs consist of strategically selected and planted foliage, which not only help to cool the air, but also cut down on air pollution and help reduce stormwater runoff.

“It’s a win-win,” says Koetter, the sustainability director. “Doing a lot of green roofs would be the fastest way to impact our urban heat island.”

Louisville is already making some headway. Seven years ago, there were no green roofs in Louisville; today, there are 18, covering more than 3.3 acres. This is thanks, in part, to subsidies provided by Louisville’s Metropolitan Sewer District, which prizes the roofs because of their ability to reduce stormwater run off. The Louisville city government will soon begin to provide its own incentives, chipping in up to $10,000 to match the MSD’s grant.

But green roofs aren’t feasible on every type of building and they’re expensive. They’re heavier than a traditional roof, so the structure has to be able to support the additional weight and water. A 2008 study from the University of Michigan estimated a 21,000-square-foot green roof would cost $464,000 to install, versus $335,000 for a conventional one. But over its lifetime, the study’s authors calculated the green roof would ultimately save the building’s owner $200,000 through reduced energy needs.

“The people that do green roofs are often doing it maybe with less care for the cost,” Koetter says. “They accept and embrace that it’s going to cost a little bit more. But it’s the right thing to do.”

***

In every big city, there are “hot spots” beyond the central downtown district that contribute more than their fair share to the urban heat island effect. In Louisville, these include the city’s two airports and several giant manufacturing facilities.

Skip Miller says he can see and feel the effects of one of the city’s hot spots everyday on his way to work.

“I can tell you, it is almost predictable, about any time of year, that when you get near the Watterson Expressway, you can watch the thermometer in my truck go up,” he says. The expressway circles the older part of Louisville, which includes the urban core. Miller says he usually can see an immediate temperature difference of anywhere from one to four degrees.

Miller is director of the Louisville Regional Airport Authority and oversees operations at Louisville’s two airports: the larger international airport—Standiford Field—and Bowman Field, which is mainly used by private planes. Outside his office window at Standiford is the airfield—a vast expanse of concrete. The entire property covers 1,500 acres. Directly adjacent, is the UPS Worldport Hub, with a facility covering the equivalent of 90 football fields.

Miller says the airport already includes some features that reduce the heat island effect: The runways are lighter concrete—not black asphalt—and part of the terminal was re-roofed with lighter material for energy-saving reasons. But there are limits when working at an airport.

“By definition, airports are large, flat open spaces,” he says. “And I think by definition, any large flat open space is more of an attractant for heat than spaces that have topography associated with it or that have a lot of tree growth associated with it.”

Downtown Louisville, Kentucky. | Mark Peterson/Redux

But trees are problematic at airports. There’s a worry, for example, that too many trees will attract birds, which create a safety risk for airplanes. Any trees planted too close to the UPS cargo areas also run the possibility of harboring pests that could contaminate cargo.

And at the nearby Bowman Field, the airport authority actually needs to remove mature canopy trees. Miller says some have gotten too big, and will have to be trimmed or removed to comply with new, stringent federal safety standards. He’s waiting for an environmental assessment to determine how many trees will be affected, but says for each one removed, two smaller species will be planted in its place.

Two of the city’s largest employers—Ford and General Electric—have also taken steps to cool their campuses. At Ford’s Kentucky Truck Plant, the company is covering an expansion project with one million square feet of white roofing. A spokesman says this roofing material costs about 30 cents more per square foot than traditional black roofing. At General Electric’s Appliance Park, the company has turned 20 acres of parking lots into a park-like walking trail.

Much of Louisville's tree loss can be attributed to the city's extreme weather and ice storms. | Mark Peterson/Redux

Koetter says these efforts are important, since the heat emanating from these facilities can affect temperatures throughout the surrounding area. But ultimately, she says the greatest mitigation efforts will come elsewhere in the county.

“What we want to do is look at it holistically and come up with that big picture strategy to reduce the total contribution,” Koetter says. “The airport—we’re never going to [mitigate the urban heat island effect] on site, but we want to figure out how we can do it around the county to impact that contribution. It’s not necessarily about ‘This is a hotspot. We have to fix that hotspot.’ It’s the whole county’s issue.” And beyond.

That’s a concept not lost on Sarah Fosnight, the bartender-cum-citizen forester. Fosnight understands that planting trees in one part of the city can have positive aesthetic, environmental and health effects throughout the community. And long into the future.

“Ten years down the road, you can be like, ‘I planted that tree. And it looks awesome,’” she says. “It’s one of those things. You can volunteer three times a year and have a real impact on your city. A lasting impact.”

Correction: An earlier version of this article incorrectly reported the rate at which the disparity in temperature between Louisville’s city center and outer areas is growing. It is widening by 1.67 degrees each decade—not each year. The text has been corrected.