Urban greening to cool towns and cities: a systematic review of the empirical evidence.

With considerably increased coverage of weather information in the news media in recent years in many countries, there is also more demand for data that are applicable and useful for everyday life. Both the perception of the thermal component of weather as well as the appropriate clothing for thermal comfort result from the integral effects of all meteorological parameters relevant for heat exchange between the body and its environment. Regulatory physiological processes can affect the relative importance of meteorological parameters, e.g. wind velocity becomes more important when the body is sweating. In order to take into account all these factors, it is necessary to use a heat-balance model of the human body. The physiological equivalent temperature (PET) is based on the Munich Energy-balance Model for Individuals (MEMI), which models the thermal conditions of the human body in a physiologically relevant way. PET is defined as the air temperature at which, in a typical indoor setting (without wind and solar radiation), the heat budget of the human body is balanced with the same core and skin temperature as under the complex outdoor conditions to be assessed. This way PET enables a layperson to compare the integral effects of complex thermal conditions outside with his or her own experience indoors. On hot summer days, for example, with direct solar irradiation the PET value may be more than 20 K higher than the air temperature, on a windy day in winter up to 15 K lower.

The physiological equivalent temperature - a universal index for the biometeorological assessment of the thermal environment.

The physiological equivalent temperature, PET, is a thermal index derived from the human energy balance. It is well suited to the evaluation of the thermal component of different climates. As well as having a de- tailed physiological basis, PET is preferable to other thermal indexes like the predicted mean vote because of its unit (°C), which makes results more comprehensible to urban or regional planners, for example, who are not so familiar with modern human-biometeorological termi- nology. PET results can be presented graphically or as bioclimatic maps. Graphs mostly display the temporal behaviour of PET, whereas spatial distribution is speci- fied in bioclimatic maps. In this article, some applica- tions of PET are discussed. They relate to the evaluation of the urban heat island in cities in both temperate cli- mates and warm climates at high altitude. The thermal component of the microclimate in the trunk space of a deciduous forest is also evaluated by PET. As an exam- ple of the spatial distribution of PET, a bioclimatic map for Greece in July (Mediterranean climate) is presented.

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Applications of a universal thermal index: physiological equivalent temperature.

A hierarchical approach to defining marine heatwaves

Numerical study on the effects of aspect ratio and orientation of an urban street canyon on outdoor thermal comfort in hot and dry climate

On July 29, 1985, a hot summer day, biometeorological measurements were performed simultaneously in three different urban structures within the city of Munich and in the trunk space of a nearby tall spruce forest. Based on the results of these experiments the following thermophysiologically relevant biometeorological indices were calculated: Predicted mean vote, skin wettedness and physiologically equivalent temperature. These three indices are derived from different models for the human energy balance. They allow the assessment of the thermal components of the microclimates at the selected sites with regard to application in urban planning. The results quantitatively show the great heat stress in the urban structure “street canyon, exposed to south”, whereas in the “trunk space of the tall spruce forest” there is nearly an optimal climate even on hot summer days. Between these extremes the results for “street canyon, exposed to north” show a little higher heat load than for “backyard with trees”.

P. Höppe

Papers

Thermal comfort of man in different urban environments