Edinburgh Napier University

  In the next years the number of cities plagued by the urban heat island (UHI) will likely grow because of the increase in urban population. This will cause the increase in heat-related mortality especially among old people and people with social or physical vulnerability and the exacerbation of cardiovascular and respiratory diseases. Previous studies show that the raise in urban albedo - for instance obtained through the conversion of dark roofs into high-albedo ones - can contribute to mitigate the UHI. Recent studies have evaluated, through the use of the Life Cycle Assessment (LCA) methodology, the environmental burdens of white roofs considering
the contribution of the surface albedo on radiative forcings. However, no LCA studies have been found in published literature in which the interaction between surface albedo and urban climate has been evaluated.
The main aims of this study are:
- to evaluate the effect deriving by the urban-wide increase in rooftops’ albedo on urban climate and then on
human health;
- to broaden the application of LCA methodology to the urban environment and to increase its spatial resolution
through the use of a hybrid analysis and a multi-scale approach.
The case study of the urban-wide conversion of black roofs into white ones has been hypothesized in New York City. The case study of New York City has been chosen because it is the most populous metropolitan area in the U.S. and the mitigation of its UHI can contribute to the well-being of many people.
In the common practice the city-wide substitution of black roofs with white ones would be down-scaled to a functional unit - for instance one square meter of roof - by omitting the effect on climate and then on human health. In this study the effect of the decrease in summer temperature and the consequent social impacts (i.e., the impact on human health) have been evaluated. The impact on human heath has been evaluated in the time-horizon of 100 years and has been referred to the use-phase of the roof instead of to its supply chain.
The research has been developed as follows:
- the UHI in the city has been detected through the use of climatological data;
- the decrease in summer temperature due to the city-wide increase in rooftop albedo has been assessed through the use of an existing climatological model;
- epidemiological data have been used for assessing the decrease in mortality for natural causes during summer due to the UHI mitigation;
- through the use of statistical data, the avoided deaths, due to the UHI mitigation, have been converted in disability adjusted life years and downscaled to one square meter of roof;
- a LCA study about one square meter of white roof has been conducted and the incidence of avoided impact on human health has been calculated.
In the life cycle inventory of the white roof all the elementary flows of a common roof representative of most roofs in New York City have been considered. Just the energy use has been omitted since it varies from one building to another. Thus any generalization about it would be incorrect because it would assume that it is uniform and this rarely happens.
By the analyses it results that the raise in the city-wide rooftop albedo significantly decreases the impact on human-health impact category revealing the importance of the use of an LCA multi-scale approach especially when the urban environment is involved.