Long-term Development of Selected Climate Parameters 2013

The Grunewald measurement station is an exceptional case among the Berlin stations being evaluated here. The station of the Berlin Air Quality Monitoring Network BLUME is located within a stand of sparse pine trees of about 20 m height in the Grunewald forest. The air temperature and humidity are recorded at heights of 2 and 18 m, respectively; the wind measurements occur at a height of 27 m above ground and thus about 7 m above the level of the tree tops. The measurements of the meteorological parameters thus reflect the local climate of the adjoining forest. Due to the location, the long-term annual mean of the air temperature takes the lowest values among the Berlin stations under consideration. In contrast to the other evaluations, the monthly mean values given refer to the 25-year period from 1988 to 2012.

Long-term mean values

Table 4.2 gives an overview of the long-term monthly mean values of selected climate parameters at the Grunewald station in the 25-year period 1988-2012 under consideration.

At the Berlin-Grunewald station, too, the measurements from 1988 to 2010 were taken into account for the climate diagram. One precipitation measurement series is missing for the Berlin-Grunewald station (cf. Tab. 4.2) because primarily aerosols are measured within the Berlin Air Quality Monitoring Network and only a few meteorological parameters are recorded in addition.

The following figures show wind direction distributions at the Berlin-Grunewald measurement station in the period from 2001 to 2010. In addition to the mean long-term wind direction distribution, distributions for low-wind conditions with speeds up to 2 m/s as well as conditions with wind speeds above 2 m/s were evaluated. At this measurement height, low-wind conditions occurred in 38.1 % of the cases in the period under consideration. Wind speeds above 2 m/s occurred 61.9 % of the time. Due to the measurements at a height of only about 7 metres above the trees with a height of 20 m, the lowest wind speeds were recorded here among the stations evaluated. The red ring lines in the diagrams indicate the mean frequencies of occurrence of the wind direction in the respective period under consideration in percent. The distance between ring lines corresponds to 1 %.

The number of summer days and hot days is also increasing at the Berlin-Grunewald station. With a plus of about seven summer days and four hot days, the increase is not quite as marked as at the other stations evaluated (cf. Fig. 4.5). Here, too, it has to be taken into consideration that several weeks of measurements were missed in 1993 between June 4 and September 12.

For the years with a strongly positively deviating number of threshold days, on the one hand the year 2003 is notable, in which very warm conditions prevailed over a long period, leading to a high number of summer days. However, in 2006 significantly higher temperatures than in 2003 were measured over a shorter period, leading to the maximum number of heat days during the entire measurement period.

The Berlin-Grunewald station records by far the fewest summerly threshold days due to the location in a forest area that is peripheral by Berlin standards.

The measurement period being shortened by at least 7 years would tend to play only a minor role in this context, as the preceding years had significantly fewer threshold days (cf. Fig. 3.6 for Dahlem).

Complementing the rise in summer threshold days, the number of frost days decreased in the trend at the Berlin-Grunewald measurement station, if only by about 6 days, whereas the number of days with a maximum temperature under 0 °C (ice days) increased by the same amount (cf. Fig. 4.7).