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A microclimate classification of the entire Bologna Municipality has been carried out in order to give a tool to the local administration in the drafting of the General Urbanistic Plan (PUG). The city was classified considering the variation of air temperature as a function of the surface characteristics, the vegetation fraction, the building density and the H/W ratio (height to width). Starting from the microclimate analysis carried out with fluid-dynamic modeling (Envi-met) for some areas of the city of urban interest, the air temperature variation was correlated to the physiological equivalent temperature (PET) in order to make a classification of physiological well-being for the resident population. An urban map of a normalized microclimate well-being index (BMN) has been obtained to give support when private, and public actors want to regenerate part of the city, taking into account the climate-centered approach for the development of a sustainability city.

The human fingerprint called urbanization is a widespread phenomenon that has assumed increasing importance over the years, leading to the fact that more than half of the world's population actually lives in cities. The explosive and sudden growth of the urban settlements increased the vulnerability of their governing systems in terms of managing capacity as well as ability to defend citizens from environmental risks. The issue of climate change strongly enhances this vulnerability and imposes to fully reconsider the way we planned the urban development that characterize the city itself. To govern this problem policy actions, based on a strong scientific evidence, is necessary to address adaptation and mitigation strategies for the urban environment. In this frame the word resilience, defined as the capacity of a system to overpass a critical situation, is utilized in the regeneration processes and has to be considered an integral part of the processes of construction of the city itself.

This work reports on the main physical processes that arise in the environment of the megacity from the “urban metabolism”—the complex interactions of the climate with the activities performed in the city and its built structure and texture—as well as on associated large-scale processes that generate hazards for the megacity’s inhabitants. It is estimated that in a few decades most of the world’s population will live in urban centers. Both the growth of megacities and climate change will increase the vulnerability of huge sectors of the population to climatic consequences of the urban metabolism. These include urban heat islands, pollution, and extreme weather events such as heat waves and floods. Developing policies to mitigate these threats will require integrating scientific knowledge with management skills, communication among cities about effective approaches, and taking into account residents’ needs for health and the capacity to live safely.

This chapter addresses the problem of city resilience to climate change and to the applicable methodologies to improve the capacity to ameliorate the population wellbeing. Future scenarios of the physiological equivalent temperature indicate the magnitude of the phenomenon. The best available technologies to mitigate such problem seem to be the utilization of vegetation in open spaces, including roof top farming. The modelling of real cases demonstrate the effectiveness of such green improvements, encouraging policies to greenness.

Architectural modification of existing urban morphology sometimes result as improvements of aesthetic characteristics of open spaces but could produce detriment of pre-existing wellness for residential population. An example of ex-ante/ex-post study allows assessing a methodology devoted to planners for the maximization of physiological wellbeing.

An experiment aimed at comparing particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) concentrations produced in a road tunnel by buses is described. The experiment took place in 2001 in Bologna when a couple of buses belonging to the public transport fleet where driven backwards and forwards in a road tunnel closed to all other vehicles. Buses run in the tunnel for 8 h a day for 4 experiment days, each day using a different fuel: biodiesel, diesel–water emulsion, diesel–water emulsion with low sulphur content and commercial diesel. Average daily concentrations of PM of different sizes and of 12 PHAs were measured and comparison between different fuels was attempted in order to assess “real-world” exhaust emissions of different fuels. Due to heterogeneity of experimental conditions in different days and the relatively large measurement uncertainties, the effort was only partially successful, and it was not possible to state any firm conclusion on fuels reliability even if some indications in agreement with literature were found. Nevertheless, the experiment and the data analysis method developed could be of interest as a methodological approach for future experiments aimed at evaluating “real-world” exhaust emissions of single vehicles.

Experimental observations of anomalous extinction in rural fogs by means of trichromatic distant contrasts are explained in terms of Foitzik's suggestion about the loss of forward scattered daylight intercepted by the target.

Koschmieder's contrast reduction law has been verified in medium visibility conditions by means of distant contrast measurements of two or more black targets placed at different distances from a telephotometer, as well as by comparing the contrast with transparency measurements. On the contrary, in foggy conditions the measurement results do not obey the law and markedly disagree with transmissometer readings. By reexamining Koschmieder's equations in the light of Foitzik's suggestion about the dependence of a target apparent luminance in fog on its geometrical dimensions, the following results are obtained: (i) contrast reduction law does not hold in fog because the target apparent luminance depends on the droplet size distribution, and (ii) this fact is entirely due to the truncated integration over the scattering angle of the air luminance gradient in the view direction because of the target's finite dimensions. These statements are confirmed by field experiments’ results.