In recent years there has been an increasing demand for a better understanding, and consequently modelling, of wind flow and pollution dispersion in built-up areas (such as cities). This task is greatly facilitated by the recent availability of high-resolution 3-D urban databases, which can be used for the analysis and measure of city geometry (urban morphometry).

Urban morphometry provides a new range of parameters that can easily be calculated for urban areas and used as input for meso-scale and urban dispersion models. This paper reviews a number of these parameters and shows how they could be calculated from urban Digital Elevation Models (DEMs) using image-processing techniques. It builds on the recent work by Ratti et al. (2001), extending the number of parameters that can be calculated by the analysis of DEMs and focussing on their spatial, vertical and directional variability (such as changes of the aerodynamic surface length with different orientations and from one urban portion to another within the same city). Results are calculated and discussed for a number of North American and European cities.

Also, a model for the determination of the wind speed within the urban canopy is derived and discussed. This is based on an extension of Cionco's work (1965 and 1972) on the estimation of wind speed profiles in a vegetative canopy. The model that has been derived makes use of the vertical variation of both the building packing density (lambdaP) and the frontal area density (lambdaF) calculated from DEMs. This avoids using the value of the wind speed just above the canopy (as done by Cionco), which is difficult to measure because of the large wind speed gradient within a small height range.

References

Cionco, R. M. (1965): A Mathematical Model for Air Flow in a Vegetative Canopy. Journal of Applied Meteorology, 4, 517-522.

Cionco, R. M. (1972): A Wind Profile for Canopy Flow. Boundary-Layer Meteorology , 3, 255-263.

Ratti, C., Di Sabatino, S., Britter, R., Brown, M., Caton, F., Burian, S. (2000): Analysis of 3-D Urban Databases with Respect to Pollution Dispersion for a Number of European and American Cities, Water, Soil and Air Pollution-Focus (forthcoming).