The urban heat island phenomenon, caused by human actions and climate change, is occurring more and more around the world. It is a circumstance where urban centers are warmer than their surrounding rural areas.
This temperature difference can be very problematic when heat waves hit big cities for a number of reasons. For example, increased temperatures can increase energy consumption and increase the amount of air pollutants and greenhouse gases that are emitted.
But these heat islands (UHIs) also are problematic for individuals experiencing heat stress — which can cause heat injuries that sometimes lead to death — and can exacerbate global temperatures.
It's a rising concern that's being met with research on the subject — with the hope that the research can inform solutions and result in action. Here are some solutions that can help reduce the impacts of the urban heat island effect.
Increase the green
Preserving and increasing the green space and canopy cover in urban areas can have a significant impact on how warm a city is. With increased canopy cover, the potential for more shade exists and consequently more cooling effects. Most of the time this means planting more trees to increase tree canopy cover. But deciding where to plant trees in a city is crucial to the success of the trees and the cooling that they provide, as well as crucial to making sure that the urban canopy is distributed fairly.
Aaron Ramirez, an assistant professor at Reed College, and Hannah Prather, a postdoc in Ramirez’s lab, employ translational science when conducting their research, where they incorporate managers and other stakeholders into the process of research so that conversations can be started right away about how to act upon the research.
They are working with the City of Portland to reduce the canopy disparities and make sure that less wealthy communities are not more adversely affected by the urban head island effect.
“Our research interests in this area are focused on how UHIs drive increased tree stress in urban forests,” Ramirez said. “This is an important potential feedback loop whereby communities already underserved could experience higher rates of tree stress and mortality, which would strengthen the urban heat island effect.
"In our work, we are developing new methods for measuring tree stress in the urban landscape and working with managers to explore ways to prevent these dangerous feedbacks between increased tree mortality risk and human health risks.”
Management decisions, informed by their research, could be anything from updating approved planting lists to including more drought-tolerant trees to changing how the city manages irrigation of city parks. This is especially important for Portland and other cities that have some of the highest urban head island effects around the country. Portland, ranked No. 4 in the difference between rural and urban temperatures, is up to 19 degrees hotter in urban areas, while No. 1-ranked Las Vegas has a difference of up to 24 degrees.
Increasing the amount of green spaces in cities can happen in seemingly unlikely places. Green roofs have the ability to help combat the urban heat island effect by providing shade, reducing rooftop temperatures, and increasing insulation in buildings, which reduces energy consumption. Green roofs can even remove greenhouse gas emissions and other pollutants from the air via sequestration and storage.
The use of solar energy can have many of the same effects as increasing green spaces in cities in addition to acting as a mitigator of climate change and the heat island effect. In using solar panels, the need for non-renewable energy is reduced and fewer amounts of detrimental emissions are put into the atmosphere in the first place, which can help reduce temperatures by not contributing to the greenhouse effect.
Depending on the type of solar array installed, it can provide shading and cooling similar to that of vegetation.
Additionally, when installed on rooftops, solar panels are able to insulate buildings. In the summer months this can create a cooling effect during the day, while in the winter months it can help prevent heat loss at night. This means less cooling energy and costs in the summer and less heating energy and costs in the winter.
Vegetation is a great way to adapt to urban head islands, but how we manage man-made materials is also very important in how we react to rising temperatures.
The materials that buildings, cars, pavements and other surfaces are made of and what color they are affect how much heat is retained in those objects and how much heat stays in urban spaces.
Lighter colors have high albedo — a measure of how much light that hits a surface is reflected without being absorbed — and trap less heat than darker colors. Cool roofs and cool pavement can help lower temperatures, but there are more areas that can also be evaluated.
The Heat Island Group at Berkeley Labs is looking at cars, pavements, roofs, and walls to evaluate what materials and colors can help create cooler cities. Often this means lighter colors and more reflective materials will provide the most benefits.
The urban head island effect is a complex network of many factors, such as those discussed above. Researchers like Vivek Shandas at Portland State University point out that there are other factors to consider as well in addition to the ones already discussed. Designing our cities so that there are varied building heights, varied canopy cover, and varied street widths can immensely help reduce the heat island effect by increasing air flow that can then cool down the city environment. The hope is that research like Shandas’ can help inform city planners and managers so they can adapt to the detrimental urban heat island effect.
So: What do we do?
Whether mitigating it in the first place or adapting to the urban heat island effect, there are many ways in which researchers have the potential to work with bureaucracy to bring about much needed change. This can be accomplished by increasing urban green spaces and cover, choosing better materials to build with, planning cities in better ways by being informed by research, and reducing our reliance on energy from fossil fuels.
These ideas — along with reducing our footprints in other ways including eating more plant-based foods, reducing fuel consumption for travel, using less single-use packaging, and interacting with our legislators to let them know how we feel about a changing climate — have the potential to reduce the urban heat island phenomena and make cities safer for residents in the years to come. The research has and will continue to guide us to solutions. Now is the time to act upon it.