Simulation of the urban climate variations in connection with the transformations of the city of Nantes since the 17th century

Abstract: The paper seeks to quantify the effect of urban politics on the microclimate of the city of Nantes (France), in particular those initiated by the sanitarians in the mid-19th century to find a remedy for the insalubrity that had been developing with urban densification since the late 17th century. Intensive historical research was first carried out in order to define and date the major transformations undergone by the city, its structure (densification, then widening of the streets, filling of water courses), the lifestyle habits (heating) or the building practices (appearance of stone and paving, higher buildings, insulation). This led to the definition of 5 characteristic states of the city, in 1680, 1756, 1835, 1880 and 1945. A numerical modelling approach is then used to simulate the urban microclimate of Nantes for these 5 states. The historical information (plans, illustrations) is incorporated into a Geographic Information System in order to determine the general characteristics of the city at the different dates. These are then used to initialize the TEB model which simulates urban energy behaviour and microclimate. While air temperature increases regularly and evaporation decreases (as expected) with greater amount of mineral surfaces, the evolution of humidity is more surprising. Air humidity first increases until the 1850s due to narrower streets. Then it decreases further with the sanitarian transformations which allow the streets to become ventilated and dry. This study gives a good indication of how town-planning actions can, in the long term, influence the urban climate. [Copyright &y& Elsevier]