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Preparatory Studies

Climate and Fresh Air

Function of the area studied as regards climatic conditions in the city

Ausschnitt aus der Klimafunktionskarte (Ausgabe 1995), mit Überlagerung der Grenze des Untersuchungsgebietes, © Stadtplanungsamt Stadt Frankfurt am Main, Kartengrundlage: Stadtvermessungsamt Stadt Frankfurt am Main

The climatic importance of an area is primarily the product of its location, its topographical circumstances, and its usage structures. These factors determine the importance of an area with regard to both the small-scale, local influx of cold air as well as the general ventilation of the urban fabric and whether it is open to regional wind and air flow mechanisms.

The municipal Climate Plan Atlas (CPA) provides detailed information about the most important micro-climatic topographical conditions in the area in question. It shows the rises and falls in the land, which to a large extent determine air flow the direction, and as such the scope impacted by the cold air that arises there.

In the CPA the dotted lines mark what are known as crest lines, which, similar to a watershed, describe the extent of an area in which cold air is generated. In the section of the map, valleys and other depressions in the land are depicted by lines of two dots and a dash, into which the cold air generated on the slopes then flows and possibly – following the line of the valley – flows away, provided there are few obstacles and there is a sufficient gradient.

On the basis of the location and alignment of the contour lines and depth contours in the area in question it can be deduced that the topography between the main cemetery in the west and Huthpark in the north-east can be divided into three separate zones in which cold air is generated:

  1. The northeastern area in which cold air arises includes Huthpark and extends southwestwards to a contour line which runs from the south as far as the “Unfallklinik” hospital. In line with the direction of the main slope, the cold air that arises within these boundaries flows eastwards or directly into Seckbach.
  2. A second area in which cold air is produced extends to a contour line that runs directly south from the cemetery in Bornheim. The cold air that arises here flows primarily to the depth contour which was made more pronounced by the A 661 interstate being built through it. Cold air flows southeastwards to Seckbacher Ried via this channel. A second depth contour visible on the map, on the other hand, is of no significance for the cold air channel, as it lies at the heart of the district of Bornheim and for this reason does not correspond with surrounding areas of cold air.
  3. In line with the general direction of the slope, the cold air produced in the west flows southwestwards in the direction of the edge of the development along Münzenberger Strasse and Butzbacher Strasse.

In addition to their significance for the local supply of cold air the open parklands in the area in question, with their link to the open countryside in the northeast of Frankfurt, also serve as a channel for regional wind systems such as that from the Wetterau region. For this reason they improve the ability of these wind regimes to flow into the northeast of the city. At the same time they can encourage the local cold air to move, such that the cold air masses are more dynamic than might otherwise be expected given the modest slope and the, for the most part, strong obstacles to air flow in the area in question.


Conclusions for the Ernst May district

The existence of various fragmented cold air regimes means that as a matter of principle the impact caused by the plans can be minimized, as partial interventions in one cold air regime do not also lead to changes in the other cold air areas and the relevant impact zones and city districts. For this reason changes in the area between the cemetery in Bornheim and Huthpark would at most lead to an influence on cold air activity in southwestern parts of Seckbach and the northeastern areas of Bornheim. Usage changes to the west and south of the cemetery in Bornheim, on the other hand, would primarily affect the flow of cold air on the perimeters of the eastern Nordend district.

What is decisive, however, is that in neither case would there be any considerable negative impact on local climatic conditions, as the layout of the expanded districts and the way they have been extended means that the remaining areas of open parkland retain their importance as a flow channel. As such the actual “driving force” behind local air in- and outflow, namely the regional wind regime, will continue to ensure sufficient ventilation and the supply of cold and fresh air.

In addition, the sheer strength of the regional wind flows will ensure that these continue to reach the whole of Frankfurt, thereby benefiting the micro-climate in more central downtown areas not benefiting from the fragmented circulation of cold and hot air in the city’s outlying areas.