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Berlin Environmental Atlas

04.10 Climate Model Berlin - Analysis Maps (Edition 2009)

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Methodology

One important factor in the creation and formation of an urban climate are the soil and surface characteristics, which have been changed in the urban area in relation to the surrounding countryside. The result is urban overheating and also the local urban wind circulation. Wind and temperature as well as quanta derived from them are the dominant factors affecting the assessment of urban climate from the aspects of human bio-meteorology and air quality.

The investigation and recording of the urban climate can be carried out with the help of various methods. These include field measurements, long-range ascertainment methods, wind tunnel studies, and the application of numerical simulation models.

Direct numerical simulation models are particularly well capable of representing the meteorological quanta, which are spatially and temporally very strongly variable, due to the great complexity of the building structure.

The detailed calculation of the wind and temperature conditions in the Berlin area within the scope of this actualization has been carried out using the FITNAH (Flow over Irregular Terrain with Natural and Anthropogenic Heat Sources) model. Groß 1993 and Richter & Röckle o.J. present detailed mathematical and physical descriptions of the model. Further detailed indications for the basic structure and approach of the three-dimensional FITNAH model, and for the interpretation of the model results, can be seen herein, on the basis of an exemplary comparison with measurement data, under Methodology/Supplementary Notes.

Generally, numerical simulation models are accepted for use in many fields of meteorology, since the data obtained provide important basic information for many areas of life (cf. Overview of the Most Important Models). The weather forecast for the next 1-5 days is obtained almost exclusively by means of such complex and extensive computer models. Knowledge of possible changes of our global climate over the next decades can also be derived from such calculations. And finally, models of a similar type are used to calculate the local and the regional distributions of meteorological variables in the atmosphere (Groß 2002).

Solely by the use of models the immission characteristics of air pollutants in the atmosphere can be simulated. On basis of the FITNAH calculation results it was possible to simulate a realistic dispersion of the relevant gas nitrogen dioxide. In doing so, the flow- und turbulence fields, which have been calculated with the 3D-model FITNAH, were used. The results of the calculated NO2-concentration within green spaces are shown in the evaluation map 04.11 and explained in the accompanying text.

The above-mentioned computer models for the various scales and task definitions, and also the FITNAH model used here, are all based on the same mathematical-physical system of equations. Only in detail are there scale-specific differences.

Meteorological Framework Conditions for the Model Calculation

In addition to the internal model definitions, the meteorological ancillary conditions play a major role. During high-pressure weather situations, the local climatically relevant particularities of a landscape are particularly noticeable. Such a weather situation is indicated by a cloudless sky and an only very light superimposed synoptic wind. The extensive synoptic framework conditions were fixed correspondingly for the numerical simulations carried out here.

Notes on Interpretation of the Model Results

In the horizontal dimension, FITNAH is based on a uniform grid, and in the vertical dimension on a stretched grid. By means of a proportionate assignment of the initial parameters, such as land use, terrain altitude, etc. to this grid, only a representative value can be calculated for every grid volume, which represents a weighted mean average value of all data obtained (cf. Methodology / Supplementary Notes).

Verification of the Results of the FITNAH Climate Model

The information derived from the model runs was checked by means of data from a study of local climatic functions of open spaces in the Gleisdreieck area of Schöneberg. On the basis of an extensive comparison, the measurement results of the study were compared with the simulation results of the model application.

As a result of this comparison, a good level of agreement can be established between the results of the measurement project and the modeling of the local air-current field in the Gleisdreieck area using FITNAH.

The self-generated, local current phenomena postulated by the model calculations can largely be confirmed by the measurements. Details on flow direction and speed are within the same range. The relevant air exchange processes - small-scale, orographically caused cold-air outflow from the Viktoriapark area of Kreuzberg and thermally induced compensation currents between the open areas of the Gleisdreieck and the adjacent buildings - are recorded and represented equally, both qualitatively and quantitatively (cf. Vogt 2002a, pp. 26 et seqq.). However, a more regionally characterized compensation flow between central Berlin and the surrounding countryside cannot be confirmed by either of the two methodological approaches (cf. Methodology / Supplementary Notes).

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