Original Situation
While implementing the Climate Model Berlin 2014, a variety of meteorological parameters were calculated at different times of day and on specific threshold days as part of the analysis phase. On the one hand, they describe the climatic situation in the Berlin area on a typical summer day, and on the other hand, they form the basis for the Urban Urban Climate Evaluation Maps 2015.
In the climate analysis, special emphasis is put on the assessment of the bioclimatic burden on humans, as it is at the core of the final planning advice maps. Various indicators are available for the evaluation of the bioclimate. It is important that these are used rather than “basic” climate parameters, such as air temperature. The latter are not detailed enough in their reflection of the population’s thermal sensitivity to varying meteorological conditions.
Previous applications of the Berlin climate model used the dimensionless parameter PMV as the basis for evaluation. The 2014 version employs the index Physiological Equivalent Temperature (PET) instead, following the progress made in discussions in the field (Höppe and Mayer 1987).
As the PET is denoted in °C, it is easily accessible also to laypeople, which is its main advantage over the PMV. In addition, the PET is a parameter that has meanwhile developed into a “de facto standard” in the field and pays greater attention to aspects of environmental medicine. Results from Berlin could therefore generally also be compared with those from other cities (even beyond Germany’s borders).
Method
The calculation of the PET is based on the heat exchange of humans with their environment that transpires during daytime hours (the PET is unsuitable for nighttime evaluations; air temperature remains the evaluation factor here).
In Tab. 1, the thermal sensitivity (derived from the behaviour of a “standard person” representing an average thermal sensitivity) and the physiological load level are compared to the PET index. Optimal comfort levels set in at 20°C. Higher temperatures cause heat-related stress, while lower temperatures result in cold-related stress.
| Tab. 1: Assignment of threshold values for the evaluation index PET during daytime hours (Matzarakis 1996; VDI 2008) | ||
| PET in °C | Thermal sensitivity | Physiological load level |
|---|---|---|
| 4 | Very cold | Extreme cold stress |
| 8 | Cold | Strong cold stress |
| 13 | Cool | Moderate cold stress |
| 18 | Slightly cool | Weak cold stress |
| 20 | Comfortable | No heat load |
| 23 | Slightly warm | Weak heat stress |
| 29 | Warm | Moderate heat stress |
| 35 | Hot | Strong heat stress |
| 41 | Very hot | Extreme heat stress |
Results
The 2 pm PET values demonstrate that the heat load occurring during the day highly depends on the local shading situation. In forest areas and areas where trees and groves predominate, the heat load is moderate on cloudless summer days with strong solar irradiation. Here, the shadows cast by vegetation reduce the direct solar irradiation. This and the evaporation of water contribute to the comparatively low load potential. Green spaces in the inner city, especially in and around built-up neighbourhoods, play an important role, due to their sojourn quality. This is contrasted with extremely sunny areas, where the daytime heat load is the highest. Temperatures measured above lawns are similarly high to those recorded above impervious areas.
Visit our topic Climate Model Berlin – Analysis Maps 2014 for a more detailed description and to discover how it fits into the overall climate analysis 2014.