Bachelor Thesis
Untersuchung der veränderten Strömungsverhältnisse nach einem Dammdruchbruch im Quartier Kreuzstein auf das Stadtgebiet von Bayreuth mithilfe stationärer Langzeitmessungen und mobiler Spurengaserfassung
Support: Christoph Thomas
The atmospheric conditions in urban areas are different from those in rural areas due to various mechanisms that result in an urban heat island effect (UHI). This effect causes higher air temperatures in urban areas, leading to less snowfall in winter and a longer growing season. In addition, it enables the cultivation of species that are typically found in southern regions. However, high night-time air temperatures may pose a general health risk, especially for vulnerable groups. Within a city, night-time air temperatures are spatially heterogeneous. Particularly in areas with cold air drainages (CAD), a reduction in noctural air temperatures can be observed. However, these cold air drainages are obstructed by barriers that prevent them from reaching the city center. The main objective of this study is to investigate the dynamics of cold air in urban areas and to improve the understanding of flow barriers in urban areas. It is hypothesised that the dam restricts cold air from the south-south-east from the Sophienberg to the Quartier Kreuzstein, leading to the formation of a cold air pool on the south-east side of the dam. It is assumed that the dam between the Quartier Kreuzstein and the pond Glasenweiher is an obstacle for the drainage of cold air at night, and that the cold air can’t flow over it. In order to place the situation of the Quartier Kreuzstein and the Glasenweiher into the wider picture of the city, it was further assumed that the entire south of Bayreuth benefits from the cold air outflows from the Sophienberg. This means that there is a uniform spatial air temperature distribution and no urban heat island is formed in this area. The hypotheses were evaluated using meteorological measurements in Bayreuth. The first measurement approach used data from the citywide meteorological measurement network, which was established as part of the MiSKOR research project. Within this thesis, this network was extended by an additional micro-weather station at the Glasenweiher pond. In addition to these stationary measurements, mobile bicycle-based measurements were conducted to measure spatial air temperature distributions. It was found that the cold air pool in the Quartier Kreuzstein is only slightly developed, which means that the dam, with a height of 8-10 meter, can’t be flown over. During cold air nights, no difference in air temperature was found between the south and north of the dam. This points to a local formation of cold air at the pond or in the surrounding green areas, or to an additional drainage path for the cold air. Nevertheless, there is a significant difference in specific humidity between unsaturated conditions regarding to water vapor during cold air nights. The specific humidity at Glasenweiher is consistently higher, indicating a well-defined microclimate spatially separated by the dam. Air temperature is significantly influenced by small green or shaded areas. In the afternoon, areas with dense vegetation has significantly reduced air temperature at ground level. This thesis shows that CAD’s have a significant influence on ground-level air temperatures in the suburban areas of a medium-sized city. Due to the lower gradient, cold air drainages have difficulty entering densely built-up areas. Even minor obstacles along the flow paths of the cold air can reduce the flow of cold air. This results, among other effects, in a lower decrease of the air temperature during the night in densely built up areas. Inner-city green spaces have the potential to decrease air temperatures in the afternoon and evening. To improve the quality of urban life, especially during heat waves, sustainable urban planning should maintain cold air flow paths to reduce nighttime temperatures.