Human thermal comfort in summer within an urban street canyon in Central Europe

Regional climate models predict an intensification of extreme heat waves in Central Europe. Against this background, the significance of human-biometeorologically orientated urban planning strategies is increasing by which the impairment of thermal comfort for people in cities in the future can be minimised. Such strategies require quantitative information on factors determining human thermal comfort within different urban quarters. With respect to these problems, the joint research project KLIMES funded by the German Federal Ministry of Education and Research was initiated. Its methodical approaches and objectives are presented in this article. One part of KLIMES are experimental investigations on human thermal comfort within different urban street canyons, whose variable arrangement generally characterises urban quarters. The investigations are conducted in Freiburg (SW Germany). The experimental design and the concept to analyse the measured data related to the objectives of KLIMES are exemplarily explained based on investigations in the "Rieselfeld" quarter on a typical summer day in 2007. The internationally well-known physiologically equivalent temperature PET is used as thermal index to quantify the perception of the thermal conditions by a collective of people within cities. During typical summer weather in Central Europe, PET is strongly influenced by the radiation heat, which is parameterised by the mean radiant temperature Tmrt. Therefore, the short- and long-wave radiation flux densities from the three-dimensional surroundings of a standardised standing person representing mean properties of a collective of people in cities are analysed in detail. For the specific conditions at the stationary site "Rieselfeld" (NW-SE oriented urban street canyon, H/W = 0.49, SVF = 0.51, SW oriented sidewalk), the contribution of the total long-wave radiation flux density absorbed by a standing person to Tmrt increased during the day from about 70% in the morning to about 90% in the evening before sunset.