Temperature in Medium Low-exchange Nocturnal Radiation Periods 2000
The parameters temperature, water vapor content and relative humidity are determining elements for the characterization of local climates and are closely interdependent. The risk of excessive humidity is of additional significance as a bioclimatic factor. The overwarming of the city compared to the surrounding countryside and also small-scale local climatic effects within the city are far more apparent in extreme individual case than in long-term mean-temperature analyses. Urban climatic changes are especially evident at night, with slight clouding and low-wind weather conditions. Also, nocuturnal conditions are free of such effects as shadow throw and/or solar illumination, which cause tremendous local variations. Thus, a generalized representation of climatic parameters for the area becomes considerably easier. In the context of the extrapolation of the climate maps to the situation of 2000, only the parameter “air temperature” was updated for Map 04.04, since the variation in relative humidity essentially reflects that of temperature, and the criterion of equivalent temperature for the description of the dangers of humidity can be assessed in far greater detail by means of Map 04.09, Bio-Climate by Day and Night.
The air temperature during the course of the day for the near-ground atmosphere in cities and conurbations develops differently under low-exchange weather conditions, depending on the characteristics location, vegetation share, development structure and use. The maximums in heavily built-up city structures are moderately exceeded, and shift somewhat in the afternoon hours. The nocturnal cooling is thus itself significantly delayed, and does not reach the level of the climatically unaffected surrounding countryside. Thus, on very hot radiation days, the highest temperatures appear in Kreuzberg, at Alexanderplatz and in the high-rise residential area of Hellersdorf. The temperature decrease during nighttime hours is more noticeable in Hellersdorf, due to the agriculturally structured surroundings, than in other heavily built-up areas (see Fig. 1). Sparsely built-up and heavily greened residential areas like Zehlendorf exhibit more favorable daytime conditions. Nocturnal temperatures at the open Dahlem Field in the Grunewald Forest drop by more than 8 °C. in comparison to Kreuzberg, while the forest location suppresses the daytime temperature course, as is to be expected.
Figure 2 shows the temperature differences between various climate stations and the coldest location, Dahlem Field, for the same summer day. At 4:00 a.m. CET, the values in the station Leibnizstrasse are 9 °C above the values for the Dahlem Field; at other residential locations, the differences drop continually to the low level of the values in Zehlendorf (5.2 °C) and Frohnau (4.8 °C). The nocuturnal temperatures are remarkably low within the Tiergarten, located in the inner city.