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Louisville’s plan to combat urban heat could take a century at its current pace

The stone facade of Firth Lutheran Church in downtown Louisville is shown against a blue sky streaked with clouds. In front and to the side is concrete sidewalks and asphalt parking lots.
Ryan Van Velzer
The cool roofs on the First Lutheran Church in downtown Louisville are among more than 300 projects completed under a Metro program designed to combat urban heat.

It’s been about a decade since Louisville Metro learned it had one of the fastest growing urban heat islands in the country. The risks disproportionately impact historically marginalized neighborhoods. Experts say the city has the chance to become a national leader at combating the problem, but an LPM News analysis finds it could take a century or longer at the current pace.

A patchwork of asphalt parking lots, city streets and concrete surrounds the gothic spires at the The First Lutheran Church in downtown Louisville.

Amid the hottest days of summer, heat radiates from the city below where Church Council President Sharon Lillie points to two simple white, flat roofs. They’re designed to reflect the sun's rays and keep the church, and by extension the city, a little bit cooler.

“Yes it’s wonderfully hot standing out here,” Lillie said.

The church is one of about 300 projects completed under a Louisville Metro program designed to combat urban heat. Lillie said she’s thankful that the city is looking at the big picture.

“Scientists have told us global warming is real, and scientists have told us that white roofs are something that can help,” she said.

Louisville Metro’s Cool Roof Incentive program and urban tree planting efforts are the city’s best strategies for combating the rapidly growing urban heat island, but they’re not moving fast enough.

A cool roof on the First Lutheran Church in downtown Louisville.
Ryan Van Velzer
A cool roof on the First Lutheran Church in downtown Louisville.

Through interviews and public records, LPM News compared what the city has accomplished to the recommendations in a city-funded urban heat management study from 2016. At the current rate of adoption, it would take Louisville Metro about a century or more to plant the trees and incentivize the cool roofs necessary to meet the recommendations outlined in the study.

Study author and Georgia Tech Professor Brian Stone said the city’s current pace is not enough to avoid significant public health and economic disruption for the city.

“Louisville has information that puts it ahead of the game, ahead of other cities, and should be investing rapidly and aggressively in these strategies to avoid reaching temperatures and humidity levels where the city just can’t operate,” he said.

Kentucky is getting warmer and wetter because of climate change. The existing summer heat contributes to illness, death and higher electricity bills, and that’s expected to get worse in the coming decades. By mid-century, the state’s expected to join a heat belt emerging in the middle of the country.

Addressing the city’s role in the crisis, Louisville Metro has set a goal of achieving net-zero greenhouse gas emissions community wide by 2040. However, the budgets for departments tasked with combating and adapting Louisville to a changing climate are inadequate relative to the size of the problem.

“Louisville needs to invest significantly more to achieve our climate action and adaptation goals. While we have seen important successes in the past, we are working towards expanding them to meet our recently updated, more ambitious climate goals,” said Sustainability Director Sumedha Rao.

Urban heat solutions

The momentum to combat the city’s heat island began to build about a decade back when Stone found Louisville had among the fastest growing urban heat islands in the country.

Temperatures can vary by more than 10 degrees between parts of the city and the surrounding countryside — driven by impervious, dark surfaces like parking lots, and a lack of tree canopy.

“And that leads to high, much higher temperatures in urban areas, which can have a series of negative impacts on people, both in terms of just discomfort, but also heat related illnesses, or pollution impacts, as well as just increased energy costs for cooling and things like that in the summer,” Rao said.

Following the first study, Louisville Metro’s Office of Sustainability commissioned Stone to undertake a first-of-its-kind comprehensive heat management assessment that was published in 2016.

What's being done about Louisville's heat disparity?

The 2016 Urban Heat Management study modeled average high temperatures across the city from May to September.

Highs ranged from 89.8 degrees near downtown to 85.5 degrees, often on the eastern edge of the county.

Stone found the heat risk highest among marginalized communities living in historically redlined districts where there is less tree canopy, more sensitive populations, and fewer resources to adapt. But Stone’s research has also found that a combination of heat management strategies could cut the impact of the urban heat island by as much as half in heavily developed areas like downtown Louisville.

The most important strategies called for the city to plant hundreds of thousands of trees and replace the urban core’s asphalt parking lots and dark roofs with greener, lighter-colored materials.

In the seven years since, Louisville Metro has undertaken a number of efforts to combat urban heat. Officials have rewritten city ordinances, started new programs, worked with nonprofits and led campaigns to reverse the city’s trend of declining urban tree canopy.

The city even created a dashboard where residents can search for the number of trees and cool roofs recommended in their neighborhoods to help manage urban heat.

Green trees

At the current pace of tree planting, it would take Louisville a century to meet the goals outlined in the heat management study.

Trees dampen the unwanted lights and sounds of the city, increase property values, limit ozone pollution, offer respite from the sun’s rays and cool the air through evapotranspiration.

From 2004 until 2012, Louisville lost around 54,000 trees per year. Former Mayor Greg Fischer started a commission to look into it, hired an urban forester, and prompted the formation of the nonprofit TreesLouisville. Since then, Louisville has also adopted an ordinance that preserves more of the city’s tree canopy amid new construction.

The city completed an assessment in 2015 that found the city’s total tree canopy covered around 37%, which was on par with Cincinnati at that time, but significantly smaller than cities like Nashville and Pittsburgh.

A view of downtown parking lots from the Omni Louisville Hotel.
Ryan Van Velzer
A view of downtown parking lots from the Omni Louisville Hotel.

TreesLouisville completed its own tree canopy assessment last year. While the methodologies are not directly comparable, researchers attempted to resolve the differences and found the city’s canopy had improved from 38% to 39%, which at the very least indicated that the city was no longer losing tens of thousands of trees each year.

To get an idea of how many trees are actually getting planted every year, LPM reached out to three of the major neighborhood tree planting groups: the city’s Urban Forestry department, TreesLouisville and Louisville Grows.

TreesLouisville and Urban Forestry each estimate they plant around 2,000 trees per year. Louisville Grows Executive Director Lisa Dettlinger estimates her group was planting around 1,000 trees per year while it was involved with the Green Heart Project of Louisville, but the board is currently reevaluating whether it can meet that goal with its current staff of three.

Without considering trees lost to storms, pests, disease and development, or the trees gained through residential and commercial planting, let’s call it about 5,000 trees per year planted in public spaces.

The city’s 2016 urban heat management study recommended adding around 450,000 trees, or around 3,000 trees per neighborhood on average. At that rate of 5,000 trees planted per year, it would take Louisville about 90 years to meet the goals outlined in the urban heat management study.

“We don’t have 90 years,” Stone said. “I don’t think Louisville is going to avoid the worst, in terms of warming, at this rate of tree planting.”

Cool roofs

Similarly, Louisville Metro’s efforts represent just a fraction of what’s necessary to shrink the city’s urban heat island based on recommendations in the urban heat management study.

Stone found that policies promoting the use of light-reflective materials such as light-colored shingles yields the greatest benefits in the near term — cooling off parts of the city by as much as 3 degrees, according to a 2019 study.

It’s a simple, but far-reaching idea. White and other light-colored surfaces reflect more sunlight than dark materials like asphalt, which absorb the heat and radiate it. Highly reflective materials can be an issue on the pavement, sending heat back into people’s faces during the hottest parts of the day, so Louisville Metro officials say they decided to focus on cool roofing.

The city offers a $1 per square foot incentive up to $2,000 for residential owners, and up to $10,000 for non-residential.

Lighter-colored roofs reflect more light and help mitigate the impacts of the city's urban heat island.
Ryan Van Velzer
Lighter-colored roofs reflect more light and help mitigate the impacts of the city's urban heat island.

The program prioritizes buildings in high-heat districts such as downtown and neighborhoods in west and south Louisville where the city has historically underinvested. So far, the city has given 58% of the program funds to high heat districts including 1, 3, 4, 5, 6, 12, 14, and 15, according to city data.

Lillie, with First Lutheran, said the city’s program saved the church around $1,200 on the installation of their roofs.

In total, the city has incentivized more than 108,000 square meters of cool roofs since the program started in 2016. However, the study recommended Louisville add about 23,000 square roofs with an average size of 1,000 square meters. Given the rate of completion so far, it would take the city around 1,500 years to reach the study’s goals.

“This level of investment will not sufficiently address the heat risk,” Stone said.

‘Little staff and little funding’

Louisville's Urban Forester Barry Edgar said it’s difficult to know how many trees the city actually has without a more comprehensive inventory, which would cost at least $500,000, but the department lacks the necessary funding and resources.

The Urban Forestry department operates on a $600,000 capital budget and a $1.1 million operating budget for a staff of 22 people, Edgar said.

“And that just covers equipment and salaries for staff, it's very small considering the amount of territory we cover,” she said. “It's very hard to manage Louisville’s street canopy with little staff and little funding.”

Louisville’s two-person Office of Sustainability tasked with implementing the Cool Roofs Incentive program faces similar challenges. The department has had a bit of a tumultuous history the last few years. The city folded it into the Office of Advanced planning in 2019.

Louisville Mayor Craig Greenberg then elevated the department again, and moved it into the mayor’s office in Metro Hall. But, it remains small. Sustainability Director Sumedha Rao said the department is in the process of hiring four more people.

“[The Office of Sustainability] has been elevated and is better funded since the administration change. Our ability to execute will continue to strengthen as our team grows. For example, two of the new positions that will be posted soon are a green infrastructure coordinator and green economy coordinator,” Rao said.

Their department’s total budget is a little more than $800,000 a year.

“Louisville Metro Government will continue to advance interdepartmental collaboration, leverage diverse sources of funding, advance policies, and execute programs that reduce urban heat island,” Rao said.

Combined, Urban Forestry and the Office of Sustainability are tasked with managing urban heat, adapting to climate change and meeting the city’s goal of achieving net zero greenhouse gas emissions community wide by 2040 have a combined budget of around $2.4 million.

That’s less than half of what Mayor Greenberg and the Metro Council approved for the Louisville Zoo this fiscal year.

More heat to come

It’s hot, the hottest summer on record around the globe. The weather fortunately spared Louisville from much of the summer’s excessive heat until August when it pushed the city out of the frying pan and briefly into the fire.

Climate change made the heatwave in Louisville at least three times as likely to happen, according to researchers at Climate Central. That’s the kind of future that Louisville can expect to see more of as man-made carbon emissions fuel a warmer and wetter climate in Kentucky.

“This is the kind of event that climate change is making more likely, more frequent,” said Andrew Pershing, vice president for science at Climate Central. “It shows you that these temperatures are unusual, that they are uncomfortable, but maybe not super extreme, that those are becoming more likely.”

The climate nonprofit research group First Street Foundation finds that Kentucky is likely to become part of an “extreme heat belt,” by mid-century. As a result, Louisville is likely to see 21 days with a heat index over 105 degrees.

Information provided by the 6th National Risk Assessment: Hazardous Heat
First Street Foundation
First Street Foundation
Information provided by the 6th National Risk Assessment: Hazardous Heat

As the planet warms, cities are closing in on temperatures that no longer make it safe to be outside for extended periods. Phoenix, for example, faced a 31-day streak of temperatures over 110 degrees.

Louisville may not rival cities in the Southwest for temperatures, but it has humidity to contend with. When temperatures and humidity are high enough, the human body cannot effectively cool itself down. These are physiological thresholds beyond which people cannot work outside.

“It’s not simply a climate problem, it’s an economic and municipal operation problem,” Stone said. “You get to the threshold, you have a blackout? You have a very serious public health problem.”

Louisville as a national leader?

Heat islands form when the cities look different from the countryside around them. Cities like Phoenix, for example, can have smaller heat islands than Louisville because the desert, like the city, has scant vegetation, Stone said.

In that way, Louisville’s terroir offers an opportunity to re-make the city in the image of its lush, grass-laden, tree-filled surroundings. The University of Louisville has taken this to heart with plans to make a microforest in the middle of downtown, and research like the Green Heart project.

Few cities around the country are as well positioned to be national leaders on urban heat given that Louisville has already done the research to understand the problem, Stone said.

He recommends the city consider investing in and staffing an office of climate adaptation designed to meet the magnitude of challenges that face the city.

“I’ve not found a city in the country that’s investing to the degree that’s needed. Very few cities even know what’s needed,” he said. “Louisville’s ahead of the game because they know how many trees they need to plant.”

Ryan Van Velzer is the Kentucky Public Radio Managing Editor. Email Ryan at rvanvelzer@lpm.org.

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