Abstract
Urban areas are typically warmer than rural ones. This is mainly due to denser configuration dominated by impermeable surfaces such as buildings and roads, compared to rural areas which are less densely built and mainly dominated by open spaces. Rapid urban expansion in dense cities bares direct impact on surface and air temperature patterns within street canyons; a phenomena which is known as the Urban Heat Island (UHI) effect. Thus, several UK city councils such as Birmingham, Manchester, and London have started to develop strategies aiming at enhancing urban green systems (UGS) through trees, green walls and green roofs. Some of those strategies include considering the green space factor, and increasing green areas within the cities to improve street canyon microclimate and reduce UHI. The Mayor of London has adopted a strategy for London 2050 aspiring to transform it to be the greenest city in the world by increasing the green areas up to 50%. This paper investigates the influence of increasing the UGS percentage which is considered as a key solution to mitigate UHI effect which will, in turn, provide thermally comfortable outdoor environments for pedestrians. The investigation is undertaken by comparing the morphology of precincts and streets in relation to air temperature, mean radiant temperature and surface temperature within Oxford Street canyons in London city centre; being one of the world’s busiest streets. The results from this research demonstrate that different UGS interventions with varying percentage are required depending on particular canyon orientations and geometries. The study found that, in general, more trees would have significant thermal comfort effect followed by living façade, while high albedo pavement (HAP) came last. However, HAP had high influence on improving thermal comfort in North-South orientated streets with minor variance to trees and living facades which, changing their percentage levels was insignificant.
Highlights
Global cities are currently inhabited by almost half of the world’s population, which is expected to increase by 70% by 2050 [1]
Being able to decide whether increasing urban green systems (UGS) percentage would likely to increase the pedestrians’ thermal comfort (PTC) or not
UGSs implementation within London city centre would be different in terms of the type of UGS, its percentage, where it is applied and that would be based on street orientation where Street 1 (S1) streets does not need much vegetation as Street 2 (S2) streets that is mainly due to solar radiation and the buildings height within the canyon limits sunlight rays to reach street level due to building shading
Summary
Global cities are currently inhabited by almost half of the world’s population, which is expected to increase by 70% by 2050 [1]. The UK has more than 60% of its population living in cities, while most European countries have almost 50% living in cities [2]. The higher population densities, the higher the impact of climate change [3]. Climate change and associated heat waves may increase the number of heat-related deaths in Europe from 152,000 to 239,758 a year by 2080, leading to 50 times death rise, while in the UK nearly 11,000 persons may die every year as a result [4]. Depending on relative vulnerabilities of the population, infrastructure, ecosystem, etc.; the impact on cities may be diverse [5]. Policy makers are establishing climate change programs that require architects, planners and urban designers to integrate climate resilience in refurbishment, retrofitting and newly built
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