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Long-Awaited Study Lays Out Ways Louisville Can Beat Urban Heat Island

An empty lot along Broadway between First and Second streets.
An empty lot along Broadway between First and Second streets.

Louisville Mayor Greg Fischer will release a draft of a long-awaited study on the city’s urban heat island today.

The study by Brian Stone of Georgia Tech — one of the foremost UHI researchers in the country — lays out quantitative ways Louisville can reduce the disparities between temperatures in urban and outlying rural areas.

The term “urban heat island” refers to the difference in temperature between the two areas; Stone’s research has previously found that Louisville has one of the fastest-growing heat islands in the country.

The heat island is a nuisance for some, but for others, it’s a dangerous situation. Stone estimated that in 2012, a warmer-than-average year, 85 people in the Metro area died from heat-related causes. Taking steps to lower temperatures by several degrees could literally save lives, he said.

“We find overall that through actions that are achievable through city policies of one form or another, more than 20 percent of annual heat-related deaths in Louisville could be avoided,” Stone said.

Fischer said the study gives city agencies the data they need to tackle the problem. But he added that the way this study is designed means it will be useful for residents, too.

“Some of these problems can seem so overwhelming that an individual says ‘I don’t know what to do, I can’t make a difference,’” Fischer said. “A study like this says ‘Yeah, you can make a difference, and you can make a difference by getting together with your neighbors, and here’s what you can do about it.’ It’s a practical guide to help not just our city as a whole but individual neighborhoods and individual households as well.”

Stone’s study focuses on three main ways to help combat urban heat: replacing dark roofs and pavement with lighter materials, planting trees and increasing energy efficiency. The greatest temperature reductions come when all three are combined in neighborhoods.

Stone said overall, planting trees is the most effective way to combat urban heat. But an analysis of Louisville’s land uses suggests there’s more opportunity for cool materials in several densely populated areas.

These “cool materials” could be anything from replacing black-paved parking lots with a lighter concrete or asphalt material, to painting roofs white or replacing black shingles with gray. The Kentucky Ready-Mix Concrete Association, a trade group, has been advertising the reflective properties of concrete for years as a way to both reduce urban heat and promote the group's product.

Stone’s study takes a neighborhood-level approach, identifying how many roofs would have to be converted, how many trees should be planted and how much pavement needs to be lightened to reduce summer average temperatures by anywhere from one to three degrees.

“I think of this as a way to direct investments by the cities -- but also by the neighborhoods and by individual homeowners -- to areas that are highly vulnerable, to try to mitigate against rising temperatures,” Stone said. “If Louisville were to implement or pursue all of these objectives, I think they would be the most forward-looking city, as far as managing heat, of any in the United States.”

Now that the study is complete, it will be up to policymakers to act on Stone’s recommendations. Fischer spokesman Chris Poynter said the draft would be released for public comment for 60 days before it is finalized. During that time, he said Metro government would begin discussing the best ways to take action.

“We’re going to be having internal discussions about what policies should we implement, are there budget implications, should we have a cool roof incentive program, should every roof that the city puts on or replaces on its own buildings, should it be a cool roof?” Poynter said. “So these are the types of conversations we’ll be having around policies, both internally and externally.”

The city will also likely look to others around the country for ideas of what policies work. Some cities have already implemented policies to lighten up roofs and paved surfaces; for example, Chicago’s “Green Alleys” program is installing highly-reflective permeable pavement in the city’s alleys.

In Louisville, Metro government has also developed a database for residents to drill down on their neighborhoods and see customized recommendations to reduce temperatures. That database will be live late Monday morning, after Fischer officially releases the study, officials said. UPDATE: Here's a link to the downloadable data.

Read the draft report below.

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