METHODS OF INFORMATION ACQUISITION FOR PLANNING (MEASUREMENTS, WIND TUNNELS, NUMERICAL MODELLING)
4.3 Numerical Modelling of Flow and Transport Processes

Numerical models are based on the mathematical solution of several dependent (and/or independent) differential equations. These equation systems are usually based on physical models, which had been simplified according to the question. As the equations describing the physical urban climate processes are largely known, numerical models for many urban climate issues have already been developed so far.

Many of these models can be used (in a user-friendly package) on powerful workstations and produce significant results in a relatively short time. Experience with the application in specific cases and with the parametrisation of models is always required however. What is also frequently required as input data is a huge amount of metrological data from the area under investigation. In a specific planning case, it is therefore recommended to consult a competent office for expert opinion.

An overview of models and model applications can be found on the Internet at
http://www.met.fu-berlin.de/~dmg/promet/30_12/3_Gross.pdf, concerning modeling of traffic-related air pollution and the Guide of the State Institute for Environment, Measurements and conservation Baden-Württemberg under http://www.lubw.baden-wuerttemberg.de/

While measurements inevitably only serve analytical purposes, numerical models can also be used to calculate and present the effects of urban planning designs and future situations (similar to wind tunnel simulations). However, the application of a model delivers only limited spatial resolutions and the representation of reality is incomplete or requires input data from measurements in the particular investigation area. Furthermore, the modelled results should ideally be verified by measurements.

Wind tunnel models are used when a detailed analysis of the investigation area e.g. on flow dynamics, the dispersion of pollutants or the clarification of human-biometeorological problems is required or when questions on the wind load and wind comfort need to be solved. What is unfavourable here are the restricted possibilities to study weak-wind flows, different atmospheric stratifications, moisture fields and temporal variations of meteorological parameters (s. a. Chapter 4.2.2.3 and VDI- guideline 3783 Page 12).

The spatial resolution of mesoscale models ranges from some decametres to several kilometres. Some calculation grids can spread at the borders for a better focus on a smaller area under investigation in consideration of the surroundings. The available prognostic models ( e.g. FITNAH and METRAS) can be applied to the most diverse urban development and spatial planning issues, like the modelling of wind fields or of cold air drainages and the dispersion of air pollutants. Microscale models (e.g. ABC or MISKAM) are used for minute-scale issues with a resolution of up to about one metre. (s.a. VDI-guideline 3782 Page 1,3,5,7 and 3783 Page 6 to 10,13,14)

Besides sophisticated physical models, there is also a statistical approach (e.g. complex interpolation) to calculate and represent comprehensive information on individual climatic elements from punctual measurements. Geographic information systems (GIS) and the calculation algorithms they contain play an important role in this context. Sometimes even complex models can be integrated into a GIS or connected via appropriate interfaces. A better integration helps to optimise working processes, e.g. concerning data handling, the provision of basic data, the administration of variations and especially modelled results which must be carried forward regularly due to changing conditions. Through a synopsis, a GIS allows for the integration of further subjects (e.g. soil function, nature conservation) in the area under investigation. WebGIS functions are principally available as well. A planning management system or decision support instrument for the weighting process could thus be created on this basis, i.e. that both the planning and the simulation of environmental impacts could be completed within the GIS. Planners and decision makers can directly visualise the impacts of a plan or its variation. When planning is further advanced, a publication via Internet for public display for example would be possible.

Basic data on topography, buildings or small-scale data for land use are ideally also available within a GIS. On the one hand, it can so be easily used for the model application; on the other all GIS functions are available for data analysis and visualisation.

This allows to deduce contour maps as well as the height and direction of terrain slopes or surface curvatures from the data. Perspective views created from the data are particularly useful here as both the direction and the angle of the view (altitude) can be selected. Figure 4/14 and Figure 4/15 shows application examples.

Through ATKIS®, a nationally standardised project by the Arbeitsgemeinschaft der Vermessungsverwaltungen der Länder (Working Committee of the Surveying Authorities of the States of the Federal Republic of Germany; ADV), Baden-Württemberg"s land surveying office provides among others digital Orthophotos (DOP), as digital landscape model (DLM) and a digital terrain model (DTM). The DTM holds highly accurate height information independent of the scale (Figure 4/16). It consists of more than 35 billion topographic points, which are aligned in a regular grid. The corresponding three-dimensional coordinates were captured with a laser scan system from a plane and then further processed.

Test data can be downloaded at:
http://www.lv-bw.de/lvshop2/produktinfo/testdatencd_rom/rubrik/daten/Testdaten.html

Following you will find the description of some popular model applications: