Environmental impacts of reflective materials: Is high albedo a ‘silver bullet’ for mitigating urban heat island?

Abstract

Studies on urban heat island (UHI) have been more than a century after the phenomenon was first discovered in the early 1800s. UHI emerges as the source of many urban environmental problems and exacerbates the living environment in cities. Under the challenges of increasing urbanization and future climate changes, there is a pressing need for sustainable adaptation/mitigation strategies for UHI effects, one popular option being the use of reflective materials. While it is introduced as one effective method to reduce temperature and energy consumption in cities, its impacts on multi-dimensional environmental sustainability and large-scale non-local effect are inadequately explored. This paper provides a synthetic overview of potential environmental impacts of reflective materials at a variety of scales, ranging from energy load on a single building to regional hydroclimate. The review shows that mitigation potential of reflective materials depends on a portfolio of factors, including building characteristics, urban environment, meteorological and geographical conditions, to name a few.Precaution needs to be exercised by city planners and policy makers for large-scale deployment of reflective materials before their environmental impacts, especially on regional hydroclimates, are better understood. In general, it is recommended that optimal strategy for UHI needs to be determined on a city-by-city basis, rather than adopting a "one-solution-fits-all" strategy.

Effect of pavement thermal properties on mitigating urban heat islands: A multi-scale modeling case study in Phoenix

“…This result emphasizes the previous finding that the thermal performance of materials is determined by multiple parameters, benefits of various mitigation strategies should be compared to come up with the best solution [39]. Fig.…”

Assessment and Mitigation Strategies to Counteract Overheating in Urban Historical Areas in Rome

“…Moreover, Figure 7b, shows that cool pavements of S1 presents lower PET values than S0 at 14:00, around −2 • C, but slightly higher than S2, around +1 • C, due most likely to the contribution of the cool wall on a cobblestone pavement. This finding is in line with Erell et al [57], and it presumably depends on the reflected solar radiation, which can either be absorbed by the surrounding surfaces increasing their surface temperature [21] or directly by the human body, increasing its energy balance.…”

“…However, their interaction with the radiative environment and the higher reflection of solar radiation could have a counteracting effect [21], especially when coupled with high reflective walls, thus their use requires an attentive evaluation going beyond surface temperature and air temperature analysis, but focused on overall comfort parameters such as PET index. In addition, it could be relevant to investigate the effects that high reflective materials have, not only on the microscale but on the large scale as well, if applied on pavements and façades as well.…”

“…In fact, pavements' thermal behavior is affected by convection due to traffic movement and by shadings due to people, traffic and urban structures, and a pavement's coat is subject to rapid dirtying and wearing. However, in the last decades, cool pavements have been developed and analyzed following the same principles used for the researches on cool roofs [21,53,54]. One of the first and relevant field measurement regarding cool pavements, conducted in Flisvos urban park in the greater Athens area, shows that extensive application of reflective pavements may reduce the peak daily ambient temperature during a typical summer day up to 1.9 • C, while surface temperatures were reduced up to 12 • C [52].…”

Evaluation of the thermal performance of different cold materials for urban paving

“…Yang et al [4] found that reflective materials are becoming an increasingly popular option in urban planning, mitigating the UHI effect and its environmental impacts, especially those involving large-scale urban-atmosphere interactions, which are not clearly understood. Gago et al [5] established as urban planning strategies, contemplating the increase of green spaces, increasing the albedo of the buildings, and greater concern for pavement surfaces.…”