Designing parking lots: green is the new black
We have paved our way to climate change, but maybe we still have time to reverse it
It is okay to admit that we love parking lots, not because of their appearance but the comfort that they bring to our lives. There is nothing like the feeling of rolling on smooth asphalt whether if it driving on a new road or skateboarding on a new parking lot. And there is nothing like the feeling of driving around downtown for fifteen minutes just to find a parking lot. So we built more parking lots, a lot of them.
Parking: Lots of problems
In the early 20th century, the car industry was booming thanks to Henry Ford who introduced the first mass-produced automobile in 1908. This successful innovation had brought more and more cars to the streets, which led us to the exponential growth of new roads and parking lots. Nowadays the United States is not only home to the first mass-produced vehicle but also home to massive road and parking lot networks.
Outside of America, new roads and parking lots were also built all over the world as car culture gained popularity globally. We now facing urban sprawl as a result of car-centric infrastructures like drive-thru restaurants and strip malls. Parking lots have changed our city landscape forever, not just the appearance but also the way our landscape functions. Today our natural landscape is just a sea of asphalt that floods our cities with problems.
Stormwater management
Our cities are indeed flooded with consequences from parking lots. Stormwater management is a major challenge for every city around the world, including drainage and stormwater treatment from impermeable surfaces like roads and buildings. Not surprisingly, replacing our natural landscape with asphalt parking lots only worsens this problem.
The existing natural landscape has multiple ways to drain off stormwater like evapotranspiration, surface runoff, and base infiltration, which altogether help gradually manage stormwater. However, impermeable paved surfaces like parking lots interfere with the natural water flow, mostly by increasing surface runoff and decreasing subsurface infiltration. Most of these surface runoffs will be drained into our sewer system and drained into water channels such as rivers. This interference of natural stormwater flow is the source of many problems.
Flooding is the first problem that we often come across with our stormwater system. Even though our storm sewer system is designed for overflow, the extreme weather from climate changes has shown us that our cities are not prepared. For example, the recent hurricane Ida broke New York’s hourly rainfall record, made the city to declared the first flash flood emergency, and killed at least 43 people. On top of that, the ever-growing road and parking lot network does not help with this problem. In fact, an article from Scientific American mentioned that “on average across the U.S., every time a city expands roads, sidewalks or parking lots by one percentage point, the annual flood magnitude in nearby waterways increases by 3.3 percent.”
Besides increased runoffs, water pollution is another major issue caused by impervious parking lots. Unlike in a natural landscape, the surface runoff from a parking lot goes into the storm sewer system rather than passing through a network of wetland and creeks to help filter sediments and retain runoff. And instead of being connected to a water treatment plant like our sanitary sewer, storm sewer is often connected directly to water bodies like waterways, lakes, or rivers. As a result, stormwater from an urban area often carry pollutants like road salts, bacteria, oils, pesticides and other micro waste into our storm sewer and directly into watersheds like streams or rivers. Over time these pollutants will decrease the water quality and damage natural habitat for plants, fish, and other aquatic species.
Heat island effects
Permeability is not the only concern when choosing material for parking. For many years asphalt has always been the most popular material when comes to parking lots due to its affordability, durability, and ease of repair. Even though concrete is more durable and easier to maintain as an alternative, asphalt is still a far better option when considering the construction time involved especially for public development. However, this seemingly perfect material is the main contributor to the heat island effect due to its dark colour.
The thermal image shows the temperature difference between dark and light surfaces with the new dark asphalt surface at a much higher temperature. The reason for this difference is that asphalt has a much lower albedo value compared to other surfaces like concrete or grass. National Snow & Ice Data Centre (NSIDC) explained the Albedo in detail below:
Albedo is a non-dimensional, unitless quantity that indicates how well a surface reflects solar energy. Albedo varies between 0 and 1. Albedo commonly refers to the “whiteness” of a surface, with 0 meaning black and 1 meaning white. A value of 0 means the surface is a “perfect absorber” that absorbs all incoming energy. Absorbed solar energy can be used to heat the surface or, when sea ice is present, melt the surface. A value of 1 means the surface is a “perfect reflector” that reflects all incoming energy.
This means a darker surface like asphalt reflects less heat from the sunlight, therefore, has a much higher surface temperature. And with the extensive network of roads and parking lots that are made of asphalt, our cities have become centre for heat islands in summer days. It gets even worse with climate changes when heatwaves are increasing in both frequency and intensity. We have managed to pave our way to these climate problems, however, there is still a chance for us to fix them.
Green is the new black
Since there is still a lot for teleportation technology to catch on and replace the car industry, parking lots will not go away any time soon. However, parking lots don’t have to the problem if we design them in a more environmentally-friendly fashion.
Tree canopy
Planting trees seems to be a natural solution when it comes to greening our urban area. Tree planting is quite affordable when compared to other methods, and most importantly, effective. In fact, the thermal image below shows the drastic temperature difference of areas shaded by tree canopy and areas without tree canopy.
However, one of the biggest challenges for trees is the growing condition. Trees in urban areas have to face issues like lack of soil volume, lack of watering, or pollutants from road runoffs. That’s why developers need to spend money and effort in designing and maintaining trees’ growing conditions to keep the trees healthy.
Low impact development (LID)
As climate changes are getting worse and worse in recent years, planners and designers have become more environmentally conscious with their works. They have developed a series of new strategies that can minimize the impacts of built infrastructure to protect and restore the natural landscape, which is often known as low impact development (LID). As the name suggests, LID practices sustainable stormwater management design that produces as minimal changes in site drainage as possible. LID can be applied through various methods such as permeable pavers, infiltration trench, rain storage, or a combination of them.
Permeable pavers
Permeable pavers are a great alternative for asphalt to deal with stormwater runoff problems in parking lots. As the name suggests, permeable pavers allow water to infiltrate the subsurface through a small space between pavers, which helps reduce the surface runoffs from the site. Since the parking lot is made of a large paving surface, permeable pavers can benefit the site drainage greatly and filter some pollutants and bacteria such as Phosphorus and E.coli according to a U.S. Geological Survey study. The only problem is that these sediments can clog the gaps between permeable pavers, which will reduce the infiltration rate of the paving. This issue can be fixed with timely maintenance using street cleaners to remove the accumulated solids and sediments.
Bioswales
Bioswales are another great LID solution to help with site drainage, in this case, parking lots. NACTO described bioswales as “vegetated, shallow, landscaped depressions designed to capture, treat, and infiltrate stormwater runoff as it moves downstream”. Bioswales are designed with engineered soil mixture and native planting to help slow down runoffs rate while cleansing the stormwater. Plus, bioswales once established require almost no maintenance with minimal water need and resilient native plants. Now with a combination of bioswales, permeable pavers, and tree plantings, we can design a much better parking lot both environmentally and aesthetically.
The future parking lot
While we can spend all the effort to design a greener parking lot, it still does not make sense to spend all that effort money to build space for empty cars, or empty lots most of the time. Sooner or later, we will have to move away from parking lots, and replacing with more purposeful developments. Indeed, we have already started to see people taking over parking spaces in different ways. The Park(ing) Day began in 2005 as an art project but since then has gained popularity all over the maps.
Some cities have realized the excessive space for parking lots and redeveloped them with new infrastructures. For example, an article from Fast Company has featured Dallas, a car-dependent city, turning their parking in parks and mixed-use development. In Canada, the Complete Streets movement is replacing street parking with protected bike lanes and widened sidewalks. All over the globe, we can obviously see the need for better public transit, affordable housing, and public spaces, not more space for cars and only accessible by cars.
