Unlike (Map 04.06 SenStadtUm 2001b) Daytime and Nighttime Surface Temperatures, the present map calculates a long-term mean situation; it does not depict any individual situation. The temperature spans are thus of course compressed; the minimum and maximum temperatures are less conspicuous.
Long-term mean temperatures in Berlin and the nearby surrounding countryside range from slightly below 7.0 to slightly above 10.5 °C. How high these urban-area-caused values can be more clearly appreciated by a comparison with values at other geographical latitudes. Long-term mean temperatures above 10.5 °C do not appear again until the area of the Upper Rhine Valley, far to the southwest (Walter and Lieth 1964).
A comparison with the 1993 edition of this map shows the climatic effects of construction activity in the city, which as a rule expresses itself in a rise in the temperature level. At some places however, e.g. the areas of the Postal Stadium, and Adlershof (the former Johannisthal Airfield), it was also possible to make corrections in the assignment to temperature classes, due to the now-improved data situation. Here, temperature conditions have to some extent improved, drop toward the level of the surrounding environment.
Within the inner commuter-rail ring (S-Bahn-Ring), three large open areas cause the formation of in some cases very cool zones. These are:
- the Great Tiergarten,
- Tempelhof Airport, and
- the Charlottenburg castle grounds.
They serve to break up the urban "heat island," which would otherwise be contiguous. This applies particularly to the Great Tiergarten and the Prenzlauer Berg People’s Park near the inner city, the effect of which is amplified by its connection to other green open areas. Former railway switchyards which are presently overgrown with ruderal vegetation, such as the Gleisdreieck South Terrain (Südgelände) corridor, also play a similar climatic role.
The South Terrain and such other areas at the edge of the inner city as the Treptow Park/ Plänterwald and the Rehberge People’s Park also have a favorable effect.
The structural development of the last 10 years has been characterized by about 30 major and numerous smaller construction projects in the inner city. Not all measures were completed by 2001 – the new Lehrte Central Station is a prime example. It is, however already apparent that the climatic conditions have worsened to the south and east of the Great Tiergarten. The area of the highest temperature class (>10.5 °C) has now merged with the "heat island" of Mitte along a line from Potsdamer Strasse through Potsdamer Platz to the east of Friedrichstrasse. Within the Great Tiergarten itself, no remaining major areas of temperature class >9.0 °C could be ascertained (Vogenbeck 2000).
The other residential, commercial and industrial areas bordering these central areas are warmer than 10 °C. These including the Spandau and Potsdam city centers, sections of Siemensstadt, and the industrial and commercial districts of Adlershof and Schöneweide. With the reduction of the density of development and the approximation to the outskirt areas of Berlin, the mean air temperature is decreasing continually.
In the Berlin forests, the mean temperatures are below 8.5 °C, in some cases even below 8 °C. This applies, too, to the woodlands and open fields to the south of Berlin. In the surrounding countryside to the east, north and west of Berlin, there are extensive areas with 8.0 °C or less, which even drops below 7.5 °C in the flat valleys. The Döberitz Heath and the pastureland east of Schönwalde are very cool locations, with mean temperatures below 7.5 °C. This is due primarily to the strong drop in nocturnal temperatures. The moderating influence of bodies of waters is also very apparent. The mean temperatures in the Havel, Spree and Müggel Lake areas are generally between 9.0 and 9.5 °C.
The temperatures of large high-rise residential areas in the east, like Marzahn and Hellersdorf, have conspicuously lower temperatures than those in West Berlin, such as Gropiusstadt and the Märkisches Viertel. This is certainly due in large measure to the fact that the high-rise residential areas in East Berlin were built with more extensive open spaces. Their location at the edge of the city also provides them with more exchange with areas less negatively influenced climatically.
The relationship between mean temperatures and the number of frost days has been mentioned above. A decline of about 0.5 °C in mean temperature causes an increase of about 10 frost days. The great temperature difference between Berlin and the surrounding countryside, resulting from different use structures, corresponds to extremes of 55 and 120 possible frost days, respectively.