Louisville’s climate is going to face significant changes over the coming decades. One of the most well-known problems facing us is the expected shift in temperature. On a global scale, many nations and international agencies have set a goal to not exceed 1.5 or 2 degrees celsius of warming. It is likely we will miss both of these targets within the next sixty years, and we may have already exceeded 1.5 degrees, although this is still disputed.
This change in temperature will have a litany of global effects that will minimally impact Louisville (directly, at least) such as coastal flooding, beach erosion, salinization of water supplies, and more. We are not on the coast, and 2 degrees does not sound all that bad, but the temperature shift is simply an average increase. Localized changes caused by global climate change will be much more significant, and Louisville will likely experience quite a few.
The University of Maryland Center for Environmental Science - Appalachian Lab released a tool that allows you to see how a city’s local climate will shift over the next sixty years by comparing it to another city or region. Louisville’s climate in sixty years is expected to be similar to that of Oil City, Louisiana’s current climate. This means winters that are 9.4 degrees (F) hotter and summers that are 10.8 degrees (F) hotter. If you wish to grow old somewhere with a climate similar to Louisville, you will have to move to Moncton, Canada.
The ten or so degree increase in temperature may be higher in more urbanized areas, as the urban heat island effect is exacerbated by climate change. This drastic increase in heat means all cities will have to adjust their urban form in order to account for it, and Louisville is no exception. Failure to adjust can be deadly, especially for any young people reading this. As you age, your body becomes less efficient at regulating its temperature. As climate change increases temperatures, and heat waves become more common, vulnerable groups such as the elderly will be most at risk.
Considering all this, how can Louisville’s urban form change in order to meet the challenges brought by higher temperature? What policies have been utilized in other cities that may also work here?
Shade, shade, and more shade.
Shade is one of the most vital tools in combating urban heat. The urban heat island effect is caused largely by direct sunlight impacting impervious surfaces like roads and parking lots. Over the course of the day, these surfaces absorb the heat from the sun, and release it back out at night. The simplest and most effective way of stopping this is just making sure a lot of that heat never reaches the ground by shading it out. Generally, shade comes from two places in a city: trees and the urban form itself.
Trees are probably the most efficient and sustainable way to cool an urban environment. Trees provide shade for one thing, but they also cool via evapotranspiration: the evaporation of water off of their leaves, providing a kind of natural air conditioning. The combined effects of tree shade and evapotranspiration have been shown to reduce surface temperatures of concrete up to 19 degrees (C). They also reduce the ambient air temperature around them, especially when combined with grass and other green surfaces.
While trees are generally recognized as universally beneficial for reducing urban heat, a significant barrier to increasing tree canopy in Louisville is funding. The city does not have a dedicated funding mechanism for tree planting and maintenance. Other cities have adopted funding mechanisms that may provide a model for Louisville. Washington D.C. has a tree fund that is paid into via a plastic bags tax and enforcement of their tree ordinance. Cincinnati requires a special assessment of all properties adjacent to public right-of-way, charging 31 cents per foot of street frontage, generating 1.9 million dollars annually for tree planting and care. Mount Rainier charges property owners with 150 sqft of impervious surface a yearly fee which goes back towards the city’s trees. These are just some potential funding solutions, many options exist.
The other main source of shade in an urban environment comes from the buildings, awnings, etc. that surround you. It is probably not the best solution to block out the sun with skyscrapers, but shade coming from “built shade” can play an important role in cooling urban heat. Some places may not be optimal for trees for one reason or another, and some species may begin to struggle in a Louisville that is 10 degrees hotter.
This built shading can take a wide variety of forms. Usually it is seen in the form of canopies spread between poles or buildings. This type of shading is most often seen in more arid cities with limited tree canopy such as Phoenix or tropical cities such as Singapore. Construction of built shading is largely up to private developers, but Louisville can build its own in certain public spaces or change regulations to make them easier to build. It is also worth noting there has been some research into integrating greenery into these structures, but implementations are currently limited.
Passive cooling and solar integration
Passive cooling is about as old as civilization itself and yet a somewhat forgotten technology. How we build cities fundamentally changed with the invention of air conditioning. Older buildings, especially offices, were built with smaller rooms and many more windows to allow for natural cooling when A/C was not an option. This difference in design extended to the presence of awnings on many windows. This is clear when you look at any photos taken of cities before the 1950s. Some older structures also utilize windcatchers, or something similar, to maximize airflow.
We have A/C now, though, why would anyone want to change this? A/C as it exists now is energy intensive, contributing to climate change through energy consumption. Beyond that, it has been shown to increase local air temperature through waste heat output. Using less A/C will contribute to lowering urban air temperatures, so building design that minimizes need for it will be beneficial.
Passive cooling can also go hand-in-hand with wider solar adoption to help curb the energy demand component. Solar panels generate the most power when A/C is needed the most and have been shown to reduce the environmental impacts of A/C use. The largest barrier to both of these, as of now, is cost. Solar costs are likely to go down, as they already have, as adoption spreads. Passive cooling can also be expensive or inconvenient to implement, but increasing energy demands may make it more appealing in the near future.
Reflective surfaces
The primary cause of the urban heat island effect is the presence of impervious surfaces. Dark colored surfaces, such as black and gray asphalt, will absorb way more heat than a similar surface with a light color. This has led some city governments to adopt policy that mandates or incentives the use of light colors for rooftops and impervious surfaces. This can reduce temperature in heat waves by around 2 degrees (C). This comes with the caveat that it can reduce building temperatures in the winter, increasing heating use and therefore emissions.
Reflective surfaces, if used in Louisville, would primarily be implemented in downtown and surrounding neighborhoods. Around 80% of downtown’s surface area is covered by either parking lots, buildings, or roads that contribute to the urban heat island effect.
Zoning reforms
Zoning may not seem as exciting or world-changing as other potential changes, but it plays an important role in Louisville’s design. Zoning’s impact on the environment is primarily connected to density. The denser an urban environment, the cheaper it is to deliver services, and the smaller the environmental impact. This means that suburbs and rural areas are more emission intensive, but they also tend to be cooler due to green space access.
Berkeley mapped zip codes by their average carbon footprint, which indicated that the most urban parts of Louisville have the lowest footprint. This conundrum with urban heat and green space access has led to zoning reforms being implemented in some cities that hope to increase both. Louisville has recently seen some changes such as the missing middle reforms that can help with the density aspect. In Toronto, the city government has implemented a system of density bonusing. Height limits are relaxed as developers build more public amenities around their new buildings, which is often park space. This creates an environment which is denser, more energy efficient, and allows easier access to green space. The increase in amenities also makes the new buildings more attractive and valuable.
The Climate Atlas
Stuttgart, Germany worked extensively to create a “climate atlas”. This atlas used information on local geography, air pollution levels, climate zones, etc. to create regulations that would help to keep the city cool and green. This includes the creation of ventilation corridors that ferry cold air through the urban environment to keep air temperatures low and minimize air pollution. These corridors are subject to special regulations such as green space requirements, anti-sprawl measures, and land preservation measures. This is technically still zoning reform in a sense, but it is guided by a guiding technical document that focuses on climate change, urban heat, and similar issues within the city.
Green Programs
Chicago is the king of green programs, offering a range of programs that contribute to the city’s overall sustainability goals. The city has a sustainable streetscape program that is used to test innovative stormwater management techniques and green additions. The green permit program allows developments meeting certain sustainability requirements to qualify for expedited permitting and permit fee reductions. Other programs include a green alley program, green roof incentives, and stormwater ordinances that require reductions in overall presence of impervious surfaces in new developments.
Singapore has compiled all of its green goals and policies into a document published every decade since 1992. Singapore has some of the most intense urban greenery in the world. The Green Plan is the guiding light used by multiple national (Singapore is a city-state) agencies, this would be a much more comprehensive form of the in-progress tree plan essentially and forms a document sort of similar to that of the climate atlas mentioned earlier.
Multiple U.S. cities have adopted land-use districts called green zones. The regulation and policy changes that apply within these districts vary between cities, but some examples include: lower business taxes based off emissions, loosening of community gardening regulations, tax incentives for tree plantings, and greening education for students and the public.
Other Solutions
The potential solutions and policy changes I have listed so far are not comprehensive. This list mostly consists of policy and design solutions that have been implemented already with some kind of success. There may be technological advancements in the next 60 years that allow for low-carbon air conditioning or new policy ideas that are more effective. Until these become clearer, though, Louisville can look to other cities to see how to combat urban heat as temperatures continue to rise.
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