The impact of vegetation types on air and surface temperatures in a temperate city: A fine scale assessment in Manchester, UK

Abstract

With increasing urbanisation and predictions of increased frequency of heat waves under projected climate change scenarios, one strategy that has been suggested to address both adaptation and mitigation for urban areas is the increased use of greenspace. A number of studies have analysed this strategy through the use of empirical, analytical methods, or numerical methods. These tend to focus on city or regional scale changes in land use with only a broad categorisation of greenspace type. This study tests seven greenspace scenarios that might be applied at a block or neighbourhood level and the resulting microclimate changes that can be achieved through such applications for a temperate city in northwest England. Using a suburban commercial site in Manchester, UK as the case study area, the research utilises the urban microclimate model ENVI-met to compare the changes in air and surface temperatures on a warm summer day in July 2010 (approximately 4°C above the rural reference July average maximum temperature). The modelling demonstrates that even in suburban areas in temperate cities a 5% increase in mature deciduous trees can reduce mean hourly surface temperatures by 1°C over the course of a summer's day. A marked increase in air temperature of 3.2°C at mid-day is modelled for the worst case scenario of replacing all current vegetation with asphalt.