Berlin Environmental Atlas
04.11 Climate Model Berlin - Evaluation Maps (Edition 2009)
Map 04.11.1 Climate Functions
The Climate Functions map illustrates the actual condition of the climatic situation relevant to planning. Thereby bioclimatic burden conditions, equalisation benefits of cold air generating areas as well as spatial relations between compensation spaces and affected spaces are represented. Since both the equalisation effects and burdens are classifiable, planning priorities can be determined to point out which built-up areas are affected by changes in compensating spaces.
Green- and open space inventory
Vegetation-covered, open spaces with a considerable cold air production represent climate- and immission-ecological compensation areas. A high long-wave nocturnal radiant emittance during exchange-poor high pressure weather conditions leads to a strong cooling of the near-surface air layer, whereby particularly city parks near emitters must be considered of being perilled in terms of immissions. The quantity of the produced cold air depends on the prevailing type of vegetation, the soil characteristics and the associated nocturnal cooling rate. All in all 699 Green-space units were demarcated, whose qualitative classification regarding cold air mass flow is shown in Table 4.
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Fig. 4: Aggregation of green and open spaces; altogether 699 aggregation areas
|Cold air generation
||Number of ISU5 block units
||Total size of category in hectares
|Low and very low
Tab. 4: Overview of the qualitative classification of the aggregated green space areas
The total area of the cold air producing surface amounts to approx. 47,420 hectares, which corresponds to an area percentage of around 53 % of the total urban area and can be regarded as high. The characteristic of cold air generation within green areas is spatially differentiated at the same time. Intra-urban green spaces are often showing a lower cold air volume flow in the center area as the subareas adjacent to development. This is traced back to the fact that the cold air, driven by the difference in temperature, has to be accelerated first, so that the flow speed increases towards the developed area. The transition area between green space and development shows the highest thermal gradient and thus the highest intensity of air exchange.
Green and open spaces with a high cold air mass flow are predominately on the outskirts of the city. Usually the larger wooded and ruderal areas, graveyards and allotments are very cold air productive .The most important spatial urban climatic contributions for the city centre are from the Großer Tiergarten, the Airport Tempelhof and the allotments Am Priesterweg. These spaces are characterized by their extensive cold air affect ranges. A large part of the Grunewald also counts as a significant open space with a connection to the city centre. Green settlement types, which are aimed towards the city centre as well as occurring slope inclinations > 1°, assist the cold air flow considerably, so that the built-up areas in Schmargendorf and Wilmersdorf have a cold air penetration of up to 2,000 m (also see the detailed explanation in the Map 04.10 (Climate Model Berlin). This, together with the allotments north of the Spandauer Damm, at the Heckerdamm as well as the Volkspark Jungfernheide and Rehberge result in a 10 km long cold air affecting area surrounding the western city centre. The green areas around the Volkspark Prenzlauer Berg and the central graveyard in Lichtenberg have a similar relevance for the eastern city centre.
Counting 3,797 block segments and a total size of approx. 37,820 hectares, this category is spatially the largest. Its green area quota makes up approx. 26 % of the total green area, which can be traced back to the extensive wooded areas on the city outskirts with high cold air volume flows mainly in the north and west of Berlin.
The compensation benefits of areas with an average cold air mass flow are also to be regarded as important. In the city centre the Schlosspark Charlottenburg, the Volkspark Friedrichshain and the Volkspark Humboldthain show a significant cold air affect range. In the southern part of the city green settlement types without a connection to park or wooded areas possess an average mass flow. The areal sum of the open spaces classified as average amounts to 16,506 hectares, which corresponds to about 35 % of the total green area.
Green spaces which possess a low cold air mass flow make up a portion of 38 % of the total with 18,221 hectares. This group is mainly composed of small graveyards, allotments and park areas with a size of up to 10 ha. These seldom possess an cold air affect range, as they are usually surrounded by buildings in a generally warmer area. An exception are those areas which are located within the affect range of green spaces with a stronger cold air production.
Green areas with a very low cold air mass flow usually cannot generate an affect range. These are small areas of about 2.5 ha, which are typically situated in developed areas. In burdened areas, however, even these small spaces can have a decisive function as climatic ecological comfort islands, as long as they feature a mosaic of different micro-climates, e.g. shadowed and sunny areas or cooling water surfaces (micro-climatic diversity). The percentage of this type of area is only 1 % with 396 Hectares. An overview of the dispersion of the respective cold air generation categories is shown in fig. 5.
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Fig. 5: Classification of green space aggregations and open spaces of the surrounding countryside according to their cold air generation
The cold air generating areas of the surrounding countryside are often in direct contact with those of the city and can hence be seen as their extension. Due to the greater distance to the settled areas the flow field is at its maximum at around 6:00 a.m. The largest cold air generating areas can be found to the north-east of Berlin. The relatively conspicuous rise in terrain height here abets a wide-ranging in-flow of cold air into the city. Numerous smaller areas are concentrated at the southern city border, while the western edge of the city can offer only two cold air generating areas. The cold air mass flow is widely characterized as high. On the other hand the smallest cold air generating area west of Frohnau shows an average potential. The relevance of the surrounding areas rises with shrinking distance to residential areas, and is highest in the areas Spandau, Marzahn as well as on the southern city border.
As was already explained under Methology, the bio-climatic load situation was determined on the basis of the z-transformation of the calculated PMV-value. This composition allows a spatial partition of the settled area into bio-climatically burdened areas on the one hand, and non-burdened or less-burdened areas on the other hand.
The latter are characterized by cold air affect ranges, a moderate overheating and an adequate ventilation due to the flows from the cold air producing open spaces. The range of the cold air flowing into the built-up areas depends upon cold air productivity and the impediment properties of the surrounding development. Fig. 6 shows the situation in the periphery of the Großer Tiergarten, whereby the concentric, nocturnal out-flow of cold air as an affected area becomes apparent. In contrast to the peripheric boroughs, the intra-urban and ventilated settlement areas often remain on a less favourable level.
In central parts of the Großer Tiergarten a zone of reduced flow velocities of less than 0.2 m/s is detected. From here the produced cold air is accelerated and, driven by the difference in temperature in consequence of the various land utilisation, infiltrates the surrounding development. Green ares indicate green spaces, whereas orange orange and red denote bioclimatically loaded housing blocks.
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Fig. 6: Simulated affect range of cold air produced in the Großer Tiergarten
The inner city itself profits from the welfare benefits of more sizable open spaces such as the Airport Tempelhof or the Volkspark Friedrichshain. Smaller, preliminary open spaces serve as "green stepping stones" and facilitate the infiltration of cold air into the developed areas.
The favourable areas are juxtaposed to stress areas with an above average heat load and ventilation deficits. This pertains to following boroughs:
The peripheral, concentrated district-centres, however, also exhibit a raised potential bio-climatic impact, as e.g. in the boroughs or districts
- Ober- und Niederschöneweide,
In addition, almost all districts feature insular housing blocks with a potential burden. However, structurally, high-rise settlements tend to have a better ventilation than portrayed in the map. Sporadically, the burden can be so great that even an existent cold air flow cannot compensate it.
Traffic-related air pollution
In particular intra-urban main roads are characterised by increased loads; according to actual estimation, at last approx. 8 % of the road network under investigation show immissions beyond the later limit value. With regard to to the potential spacious load of green spaces by nitrogene dioxide emissions caused by traffic, the constellation of areas with a high and medium cold air generation and simultaneous NO2-concentrations > 80 µg/m³ is of special interest. This is given on approx. 3.3 % of those areas with a high or medium cold air generation.
Although this surface percentage appears to be low, intra-urban green spaces can show an areawide load (Schlosspark Charlottenburg) or at least largely affected subareas (western part of Großer Tiergarten - cf. fig. 7). In view of an optimization of the climatic functions of these green spaces, the improvement of air quality at such a constellation needs specific attention.
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Fig. 7: Areas within relevant cold air generating green spaces potentially affected by traffic-related pollutants (NO2, shaded purple)
Structures which allow air exchange and introduce cold air are the central link between compensation spaces and bio-climatically burdened affected spaces. Air-stream channels should usually offer a low surface roughness, whereby lesser wooded valley and floodplain areas, larger green spaces and tracks offer the required attributes. Wide roads, because of their immission load, can only aid the climatic balance, but not the transport of fresh air. The air-stream channels are sub-divided according to process in the Climate Functions Map, where a cold air producing (partial) area can also fulfil a function as a ventilation lane.
The predominant form of ventilation lanes are thermally induced types in combination with a compensation space, which can be led back to the utilisation-based temperature differences. Exemplary for such inner city channels are the allotments at the Priesterweg which transport the cold air northwards coming from the graveyard on Bergstraße in Steglitz and from Insulaner. Furthermore the allotment am Heckerdamm as well as the Volkspark Rehberge channel a fraction of the cold air produced at the Airport Tegel towards the city centre. A number of further thermally induced ventilation lanes can be found north of the axis Tegel - Lichtenberg as well as in the south between Lichterfelde and Bohnsdorf. In the western part of the city the lanes are grouped around Spandau and lead cold air directly out of the northern Grunewald and the bordering regions towards the city. If a green space borders directly on a developed area, a ventilation lane becomes obsolete.
Predominantly orographically induced ventilation lanes are concentrated in the eastern part of the city. These are about valleys, e.g. Wuhle and Mühlenfließ, which, because of their alignment, width and terrain attributes, can be used as air-stream channels. To that effect, one can class in the western part of the city the depth line from Grunewald trough Hundekehlsee - Dianasee - Koenigssee - Halensee.
The lowlands of the larger rivers like Spree and Havel exceed this function and also possess a characteristic for superordinated air-stream and ventilation channels. They benefit the air exchange in the bordering developed areas even under strong, dominating weather conditions.
A spatial cold air out-flow is limited to areas with an inclination of > 1°, and is, because of the relatively low height differences, scarce in Berlin.
For that reason this process is interlinked to the few areas with a noteworthy inclination like that of the Grunewald and the Köpenicker Bürgerheide. Furthermore, in the northern part of the Tegeler See, Kaulsdorf and in the Forst Düppel one can assume cold air flow. The cold air generation is above average on these wooded slopes because the long-wave emission is very high, and with that the primary cooling rate. This occurs not from the ground, but from the upper treetops. Due to the size of the emanating surface the cold air can flow in and over the treetops, instead of first subsiding into the trunk area (Groß 1989).