Heat waves in Berlin, Germany - Urban climate modifications
Final Report Abstract
The project “Heat waves in Berlin, Germany – Urban climate modifications” focused on the analyses of heat waves (HW) in the mid-latitude city Berlin, Germany, and how the city modifies spatial and temporal characteristics of HW and atmospheric conditions during such events. Different types of data, ranging from observations of near-surface atmospheric variables, derived turbulent flux data, crowdsourced CWS data, and gridded atmospheric data from dynamical downscaling of global reanalysis data were collected, acquired from external sources or created, and subsequently applied in the investigations. Homogeneous climate data of 125 years were used to investigate differences between HW definitions concerning long-term mean values and trends in HW indices. Generally, an increasing trend of more frequent and longer-lasting HW in the study region was detected. Yet, specific numbers show remarkable differences between the definitions. An inner-city location displays more and longer HW compared to the periphery for HW definitions applying daily mean or minimum air temperature T. The strong impact methodological aspects can have in HW investigations was further illustrated in another study that focused on the urban heat island (UHI) effect during hot weather episodes. In that case, choosing a different location or time of day to identify these episodes can lead to contrasting results. These contrasts are strongly linked to differences in weather conditions during the episodes. Weather conditions during and before HW in comparison to non-HW periods were studied to understand alterations in the atmosphere during these episodes. Several atmospheric variables differed significantly to non-HW periods up to four weeks before HW. These findings could help in the development of an early warning system for HW based on observational data. Intra-urban analyses primarily focused on spatial and temporal variability of near-surface T. Applying high-quality data from professional stations and crowdsourced data from citizen weather stations (CWS), variability of T on the micro-scale within, and differences in T between Local Climate Zones (LCZ) were studied. It was shown that CWS data, despite their deficiencies regarding meta data and sensor location, provide additional information that cannot be obtained with standard meteorological observations. Hence, CWS are of high value in urban thermal climate analyses. Further investigations made use of data from professional stations and CWS to analyse intra-urban T variability in different applications, focusing on intra-LCZ T variability, T conditions in urban green spaces and allotment gardens, and mapping of T with high spatial resolution. An improved version of a formerly developed event-based risk model was applied in several studies to investigate relations between elevated T and mortality rates, as well as to derive thresholds for HW definitions based on locally representative heat-mortality relationships. The interaction between high T and elevated ozone concentrations was also studied. Both environmental stressors pose a significant threat to urban dwellers in Berlin, with T being the dominant of the two.
Publications
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(2017): Intra and inter 'local climate zone' variability of air temperature as observed by crowdsourced citizen weather stations in Berlin, Germany. Meteorol. Z. 26 (5): 525-547
Fenner, D., Meier, F., Bechtel, B., Otto, M. and Scherer, D.
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(2019): Contrasting changes of urban heat island intensity during hot weather episodes. Environ. Res. Lett. 14 (12): 124013
Fenner, D., Holtmann, A., Meier, F., Langer, I. and Scherer, D.
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(2019): Heat waves in Berlin and Potsdam, Germany - Long-term trends and comparison of heat wave definitions from 1893 to 2017. Int. J. Climatol. 39 (4): 2422-2437
Fenner, D., Holtmann, A., Krug, A. and Scherer, D.
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(2019): Occurrence and Coupling of Heat and Ozone Events and Their Relation to Mortality Rates in Berlin, Germany, between 2000 and 2014. Atmosphere 10 (6): 348
Krug, A., Fenner, D., Holtmann, A. and Scherer, D.
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(2020): Heatwaves and urban thermal climates in Berlin, Germany. PhD thesis, Chair of Climatology, Technische Universität Berlin, Berlin, Germany
Fenner, D.
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(2020): The contribution of air temperature and ozone to mortality rates during hot weather episodes in eight German cities during the years 2000 and 2017. Nat. Hazards Earth Syst. Sci. Discuss.
Krug, A., Fenner, D., Mücke, H.-G. and Scherer, D.
