Thermal comfort conditions within an E-W Oriented street canyon in Freiburg (Germany) during the European summer heatwave 2003

A record-breaking heatwave affected the European continent in summer 2003. Within cities the negative impacts on the well-being and health of people have been intensified by the urban climate conditions. To quantify the effects of the thermal environment on people, thermo-physiologically significant indices were developed in the modern human-biometeorology. Depending on the objectives, they can be determined by direct measurements of all required meteorological variables or modeling. The first method was applied in the two day (14 and 15 July 2003) case study to analyze the thermal comfort conditions for people within a street canyon in Freiburg (south-west Germany) during the summer heatwave 2003. The physiologically equivalent temperature PET was used as an adequate thermal index. Continuous measurements of meteorological data (air temperature, vapor pressure, wind speed as well as short- and long-wave radiation flux densities from the three-dimensional surroundings of a standing person) necessary to calculate PET were carried out at the human-biometeorologically significant height of 1.1 m a.g.l. at the northern sidewalk of an E-W oriented street canyon (H/W = 1.0) in the downtown of Freiburg. The mean radiant temperature which is the most important meteorological variable in the calculation of daytime values of PET was directly determined from the measured radiation flux densities.

Against the background of the extreme summer weather, the results are discussed with respect to different problems of urban human-biometeorology. (1) They quantify the diurnal variability of the outdoor thermal comfort for people within a specific urban street canyon. (2) They enable process analyses on the magnitudes of the influences of different meteorological variables on PET. (3) They provide an indication on the dependence of PET on the short- and long-wave radiation flux densities from vertical surfaces within the street canyon. (4) They exhibit the diurnal variation of the three-dimensional radiation flux densities within a typical street canyon. (5) The measured meteorological variables as well as the derived mean radiant temperature and PET obtained for a comparatively uniform street canyon are well suited to validate human-biometeorological models for the simulation of thermal comfort (e.g. RayMan).