9. Climate analysis maps (map-XIII, pages 1 to 12)Areas of cold air, particularities and topographic structure
The aeration of settlement areas is important, especially during inversion weather conditions. Therefore the areas producing cold air and cold air catchment areas, responsible for the fresh air supply during the night, are particularly marked on this map.
Cold air drainage areas
Cold air drainage areas are characterized by a high production of cold and fresh air as a result of the negative energy balance during the night. This is true for large cohesive open land while built-up areas and water surfaces are excepted from these areas due to a lower production of cold air.
The average production rate of cold air above open land is about 12 m┬│ per m┬▓ and hour and it increases with the slope inclination (KING, 1973). Although forests generally appear warmer, their production rate of cold air must not be underrated as the cooling degree is indeed higher above open land, i.e. the air cools down more rapidly above open land than above forests, but forests influence a bigger air volume (see also GOSSMANN, 1987).
Most of the cold air drainage areas are situated on the edge of the area under investigation where there are large meadows and arable land. Cold air drainage areas in the proximity of Stuttgart are especially Langes Feld, a fertile and agricultural landscape west of Kornwestheim, and the Filder plains.
Cold air catchment areas
Cold air catchment areas are large and cohesive areas where air temperatures are significantly lower than in their surroundings due to cold-air flows from cold air drainage areas and/or the production of cold air on the spot. These areas are characterized by a higher frequency of night frosts and a stronger probability of haze and fog formation.
The localization of cold air catchment areas on the climate analysis map includes a dynamic component as it is oriented to relative topographic low situations. Cold air catchment areas therefore have upper limits adapted to these structures. The corresponding information is taken from the topographic map and thermal maps. The thermal effect of dense settlement areas in valley zones and basins neutralizes a near-ground cold air catchment completely or partly.
All indented valleys are cold air catchment areas, like for example the valleys of the following streams and rivers: Glems, W├╝rm, Enz, Murr, Rems, K├Ârsch, Fils and Aich as well as Feuerbach valley, Nesenbach valley and Siebenm├╝hlen valley. The concentration of cold air in the Neckar Valley is mostly neutralized between Plochingen and Stuttgart by dense development.
Buildings, embankments or pieces of woodland transversal to the direction of cold-air flow lead to stagnant cold air
. The results are a higher frequency of night frosts and the obstruction of cold and fresh air flows. When the volume of cold air increases, obstacles can be overflown.
Areas with stagnant cold air caused by buildings or forest barriers are for example the areas south of Winnenden, west of Hemmingen, south of Flacht/Weissach, south of Gerlingen, south of M├Âglingen, in Ludwigsburg-Eglosheim and around Affalterbach.
Obstacles in valleys that can be overflown by increased cold-air flows can be found for example in the areas east of Sindelfingen, east of Magstadt, in Waldenbuch, Stuttgart-Uhlbach, Untert├╝rkheim, Stuttgart-Heslach, Waiblingen-Bittenfeld and Stuttgart-Plieningen.
In the case of narrowing at valley cross section
, cold-air flows are obstructed and this leads to a situation similar to the formation of pools of cold air. The narrowing of cold-air flows by buildings or particular topographic conditions can be found for example in Waiblingen (in the Rems valley), Leonberg-H├Âfingen (Glems valley), Musberg (Siebenm├╝hlen valley) and M├╝nchingen.
|© City of Stuttgart, Office for Environmental Protection, Section of Urban Climatology