Ventilation classes

During the project seven different ventilation situations were introduced representing the dominating local ventilation conditions in the study area (see table).

Ventilation situations result from characteristic combinations of climatic factors controlling local and regional wind fields as well as vertical air mass exchange processes resulting in distinct ventilation conditions. They correspond to ventilation conditions with an increased probality of occurrence compared to other areas.

The extraction of the ventilation situations was carried out with a numerical, rule-based classifier. Whereas some of them solely depend on terrain parameters (e.g. wind-exposed areas), others are derived only from land-use parameters (e.g. areas of reduced ventilation) or both (e.g. areas of cold air accumulation). Therefore the spatial pattern of the ventilation situations is based on the spatial distribution of climatic factors delineated from spatially distributed terrain and attributed satellite data as e.g. building heights or aerodynamic roughness lengths.

Code	Ventilation situation	Description
0	Indifferent areas	No specific modification of the wind field. Ventilation mostly depends on the adjacent areas.
1	Wind-exposed areas	Higher wind velocities more likely due to exposed topographic situations.
2a	Terrain-induced ventilation paths	Channelled flow of air masses due to drainage flows from upslope areas in the vicinity, or by channelling of synoptic winds due to topography.
2b	Terrain-induced ventilation on slopes	Slope winds or drainage flows along the gradient lines. Partly channelling of synoptic winds.
3	Areas of undisturbed ventilation	Undisturbed flow of air masses due to small roughness values, flow obstacles and weak or missing anthropogenic heat sources.
4	Areas of reduced ventilation	Modified flow of air masses due to higher roughness values and flow obstacles.
5	Areas of cold air accumulation	Reduced wind velocities and enhanced stabilisation of the stratification due to cold air accumulation in hollows or by barrier effects at valley narrows or at settlement structures.