Urban heat : natural and anthropogenic factors influencing urban air temperatures

The urban heat island effect is a phenomenon observed worldwide, i.e. evening and nocturnal temperatures in cities are usually several degrees higher than in the surrounding countryside. The main goal of this thesis is to understand the processes that drive the urban air temperature and the urban heat island. First, the effects of street geometry and open water bodies on the diurnal cycle of the urban air temperatures were investigated. This was followed by a search for a universal scaling of the meteorological variables into a diagnostic equation for the daily maximum urban heat island. Finally, it is explored how the daytime urban heat island is influenced by atmospheric boundary-layer dynamics and how it may induce a counterintuitive urban cool island during the morning.