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Long-term Mean Air Temperatures 1981-2010

Introduction

Climate changes in agglomerations

The climate of an urban agglomeration, unlike that of its surroundings, is characterised by major changes in the local heat balance. Reasons include:

  • changes in the heat capacity and thermal conductivity; modified wind and exchange conditions as a result of land consumption, caused by, for example, infrastructure measures and development projects,
  • decreasing numbers of areas that facilitate evaporation, due to the ever increasing degree of impervious coverage and the consequent loss of areas with vegetation,
  • climate change as a result of the global warming of the atmosphere caused by greenhouse gas emissions,
  • introduction of energy and water vapour by anthropogenic influence. Some aspects of the resulting urban climate pose a particular challenge.

These include an increased air temperature and bioclimatic burden in the summer months and a compromised air exchange between the higher atmospheric layers and the surroundings throughout the year.

Air temperatures are increased in urban areas compared to their climatically unaffected surroundings. Urban temperatures mainly depend on the building density, the local vegetation structure and the topography. In this context, the long-term mean temperature plays a key ecological role. A moderate to high increase in the long-term mean temperature along with a decrease in the number of frost days in an urban area, as compared to its undeveloped surroundings, may favour the migration of plant and animal species that thrive in the heat: e.g. an increase in the mean temperature from 7 °C to 10 °C reduces the number of frost days by half (cf. Stülpnagel 1987).

In addition to the conditions of dense settlement structures inherent in agglomerations, the effects of climate change have now become tangible also in Berlin, which further accelerate the increase in mean temperatures. Forecasts of potential developments largely depend on future greenhouse gas emissions, which Germany’s Meteorological Service (DWD) is monitoring (cf. DWD 2020), for example. According to the DWD, the mean temperatures are expected to increase between 1.1 and 3.8°C in Germany by the end of the century, as compared to the reference period from 1971 to 2000. Germany’s southern regions are projected to see a somewhat more pronounced rise in temperature than the northern regions.

Potential temperature developments and any resulting needs for action have been calculated and are available for various scenarios for Berlin. The individual project results, however, cannot be applied indefinitely, as climate modelling is ever advancing and changing framework conditions require constant adjusting (to access the latest information visit the following websites: SenUVK Climate Protection, SenSW Urban Development Plan Climate 2.0 or the Topic Climate of the Environmental Atlas).

Grid data records of site-specific measurements by Germany’s Meteorological Service (DWD) form the basis of evaluation in the current edition, which differs from the previous edition from 1961-1990. As a result, the long-term temperature distribution can now be displayed cartographically for each individual season (spring, summer, autumn and winter), in addition to the annual mean. The difference in statistical base and resulting methodology across the two editions allows only for a very limited comparison between the current results and those of the reference period from 1961 to 1990 of the Berlin Environmental Atlas.