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How hot are cities? A lot [hot]! Cities tend to be several degrees warmer than surrounding rural areas, a phenomenon called the Urban Heat Island (UHI) effect.
A large body of literature over the past 200 years has shown that urban areas tend to have higher air temperatures than adjacent rural areas1,2, the so-called UHI effect.
• Kleerekoper et al.3 summarized the causes of the development of UHI, including:
—replacement of vegetative surfaces with impervious ones of lower solar reflectance (albedo), which absorb and retain greater solar radiation
—reduction of turbulent heat transport due to dissipation of wind as a result of urban form
• Manoli et al.4 also found that the UHI is strongly influenced by the
—absence of permeable surfaces and moisture—typical of dense urban areas, where over half the world’s population lives5, a proportion that is expected to rise steadily in the coming decades
• UHI effect is particularly concerning because it is a form of heat pollution that:
—gradually corrodes quality of life and the environment
—leads to increased consumption of electricity for cooling buildings6,7,8
—leads to higher water consumption9,10
—leads to reduced thermal comfort11,12,13
—leads to deterioration in public health14,15,16
• Ziter et al.17 showed that these effects also:
—varied within a city
—correlated with the extent of impervious services at local scalesThus, it is important for urban planners and policymakers to consider solutions for heat mitigation. However, with limited budgets that need to be stretched to provide municipal services, there is a need for solutions and strategies that maximize the benefits from the limited resources available to communities to mitigate heat pollution.
From PAPER published in the journal Nature Communications by Sushobhan Sen and Lev Khazanovich, titled “Limited application of reflective surfaces can mitigate urban heat pollution” (June 9, 2021) (Please see below)
Many cities have been observed to be 2-4ºC warmer than the countryside in virtually every inhabited continent. This happens because urban infrastructure, including pavements, absorb a lot of heat as compared to natural vegetated surfaces. This heat pollution causes you to pay more for air conditioning and water, while also posing a public health hazard.
Fortunately, concrete pavements and concrete overlays can help to mitigate the problem, as demonstrated in the paper published in the journal Nature Communications by Sushobhan Sen and Lev Khazanovich, titled “Limited application of reflective surfaces can mitigate urban heat pollution” (June 9, 2021). Researchers at the University of Pittsburgh investigated the effect of modifying some surfaces in an urban neighborhood with cooler surfaces, which includes reflective concrete and cementitious coatings:
• Typical urban surfaces have a solar reflectance (albedo) of 0.20
—Reflect just 20% of sunlight
—Absorb as much as 80%
• Reflective concrete and coatings can be designed to
—Reflect 30-50% or more
—Cities like LA have already used reflective coatings on major streets to combat heat pollution, although it can be an expensive solution to implement city-wide.
Looking to find ways to decrease cost and increase usage of cooler surfaces, the researchers examined the possibility of applying them to just half the surfaces in a city. They found that this could be an effective solution— if the surfaces were selected to be upstream of the dominant wind direction. A “barrier” of cool surfaces pre-emptively cools the warm air, which then cools the rest of the city at a fraction of the cost. On the other hand, if the surfaces are not strategically selected, their effectiveness can decline substantially. This research gives urban planners and civil engineers an additional way to build resilient and sustainable infrastructure using limited resources.
Several interventions to mitigate heat pollution have been recommended in the literature:
• Green infrastructure—creation of new green spaces as well as covering existing surfaces with vegetation in the form of green roofs and green walls. It is based on the effect of latent heat from evapo-transpiration as well as shading to decrease the air temperature
• Blue infrastructure—related to green—directly uses evaporation from water stored and distributed through irrigation, urban water bodies, and low impact development to mitigate heat pollution
• Blue-Green infrastructure solutions24—the 2 have been considered together
• Gray infrastructure—involves the modification of impermeable surfaces (walls, roofs, and pavements) to counter their conventional heating effect27.
—permeable surfaces: Store water=evaporative cooling28,29 which leads to evaporative cooling
—energy-harvesting surfaces: (on the other hand) use a series of pipes embedded into surfaces as part of a heat exchange mechanism to directly transfer heat away from those surfaces30,31 and potentially use it for other applications
—reflective surfaces have a higher albedo than typical construction materials, and hence absorb less solar energy and decrease heat pollution32Among all the possible strategies, the present study focuses on the effectiveness of reflective surfaces as a heat mitigation strategy and therefore, a greater discussion on them is presented in the PAPER (see below).
From PAPER published in the journal Nature Communications by Sushobhan Sen and Lev Khazanovich, titled “Limited application of reflective surfaces can mitigate urban heat pollution” (June 9, 2021) (Please see below)
For much more on the studies such as: Abstract-see below; Introduction; Results; Benefit-to-cost ratios; Discussion; Methods; Data; Code; References; please download the paper below.
PAPER:
by Sushobhan Sen and Lev Khazanovich: “Limited application of reflective surfaces can mitigate urban heat pollution” Nature Communications Website: 12, 3491 (June 9, 2021)
ABSTRACT:
Elevated air temperatures in urban neighborhoods due to the Urban Heat Island effect is a form of heat pollution that causes thermal discomfort, higher energy consumption, and deteriorating public health. Mitigation measures can be expensive, with the need to maximize benefits from limited resources. Here we show that significant mitigation can be achieved through a limited application of reflective surfaces. We use a Computational Fluid Dynamics model to resolve the air temperature within a prototypical neighborhood for different wind directions, building configurations, and partial application of reflective surfaces. While reflective surfaces mitigate heat pollution, their effectiveness relative to cost varies with spatial distribution. Although downstream parts experience the highest heat pollution, applying reflective surfaces to the upstream part has a disproportionately higher benefit relative to cost than applying them downstream.
To download the PAPER, please go to: https://www.nature.com/articles/s41467-021-23634-7
ISCP ARTICLES on mitigating UHI and creating cooler cities with CONCRETE PAVEMENTS and COATINGS:
Click on titles to open article:
Mitigating Climate Change & Extreme Heat With Reflective Pavements
Bryan Perrie: Concrete Parking Lots—Cooler, Environmentally Friendly, & High Curb Appeal w/Low Maintenance
MaintenanceWinnipeg Canada: Concrete Best Long-Term Choice for Pavement—1st Concrete Pavements Date Back to 1903!
How Climate & Pavement Condition Determine Sealer Selection
History: 1958-1960 AASHO Rd Test “…encompassed most substantive pavement research…in the 20th century”
Cement Soaks up Greenhouse Gases
Indian Gov’t. Stresses Need for All Roads to be PCPs + Paper: “Theoretical Investigation on PCP as Sustainable Pavement Technology (SPT)”
20 Ways Concrete is Sustainable + VIDEO
Home cover photo: Fig 1: Cases Analyzed