Berlin lies in the temperate climate zone, characterised by a distinct manifestation of seasons with maximum precipitation in the summer months.
The climate in Berlin is primarily determined by air masses transported here from the southwest and northwest, mainly from the Atlantic. These air masses are characterised by humid sea air, which provides for mild temperatures when coming from southerly directions, and cooler air when coming from the north. If the air masses come from easterly and thus continental directions, they are usually very dry and may cause very cold weather periods in winter and very hot ones in summer.
However, in large conurbations such as Berlin, this natural influence is at least sometimes shifted by various anthropogenic influence factors, which are summarised under the term “heat island effect”.
The intensity of this heat island effect depends on various urban structures (building height, density of development etc.) but also on the prevailing meteorological situation (i.e. the weather conditions). This heat island effect is particularly pronounced under summerly weather conditions with low winds and high pressure, under which the air can hardly circulate within a densely built-up city. Accordingly, the temperature values are lower in the less densely built-up surroundings of the city. The general warming due to climate change additionally raises the temperature level (cf. chapter: Excursus: Estimate of possible effects of climate change). This occurs in urban and rural areas alike, so that the relative temperature differences between city and countryside essentially remain the same. However, with a rise in the general temperature level, temperature values that impose a bioclimatic load occur more frequently mainly in the cities.
Primarily elderly people react very sensitively to extreme temperatures. In our geographic areas, particularly the extreme weather conditions in summer play a major role in this regard.
In order to better quantify such loads, various threshold days are distinguished in meteorology according to the following definitions:
- Summer day: maximum temperature reaches at least 25 °C
- Hot day: maximum temperature reaches at least 30 °C
- Tropical night: minimum temperature not under 20 °C
- Frost day: minimum temperature under 0 °C
- Ice day: maximum temperature under 0 °C.
Note: In the context of these evaluations, hot days are simultaneously also assessed as summer days.
While an analysis of the current state of the distribution of climatological parameters and for the simulation or scenario formation of future states can be carried out using very elaborate climate models (cf. DWD 2010, SenStadt 2009a-b, SenStadt 2010), there are more or less comprehensive measurement data for the analysis of time periods in the past.
In the Berlin area, temperature values have been recorded regularly since the beginning of the 18th century. The Berlin climate measurement series is thus among the oldest in the world. Of course the measurement capabilities at the time were limited with respect to precision and permanence (of the measurement site), especially as these observations were not carried out by technical institutes; in Berlin they were first performed by individuals such as the parish church pastor or the teacher and astronomer Johann Heinrich Mädler (as detailed in Pelz 2007).
The longest contiguous climatological measurement series in the Berlin area is the one in Potsdam; it goes back to 1893. In 1908 the Berlin reference station in Dahlem begins to record the climate (three times per day), though Dahlem was not part of Berlin at the time.
The statistical analyses published here are essentially based on partial results of the project “GIS-based modelling of characteristic quantities relevant to urban climate on the basis of high-resolution data on buildings and vegetation” ("GIS-gestützte Modellierung von stadtklimatisch relevanten Kenngrößen auf der Basis hochaufgelöster Gebäude- und Vegetationsdaten") (GEO-NET 2014) as well as the results of a student internship (Knerr 2014). This project is being funded by the European Regional Development Fund (ERDF) and the State of Berlin (Project number: 027EFRE GDI) with funding for measures for building the geodata infrastructure (GDI).