Abstract
The sky view factor (SVF) has an important role in the analysis of the urban micro-climate. A new vector-based SVF calculation tool was implemented in a free and open source Geographic Information System named OrbisGIS. Its accuracy and computational performance are compared to the ones of an existing raster based algorithm used in SAGA-GIS. The study is performed on 72 urban blocks selected within the Paris commune territory. This sample has been chosen to represent the heterogeneity of nine of the ten Local Climate Zone built types. The effect of the algorithms’ input parameters (ray length, number of directions and grid resolution) is investigated. The combination minimizing the computation time and the SVF error is identified for SAGA-GIS and OrbisGIS algorithms. In both cases, the standard deviation of the block mean SVF estimate is about 0.03. A simple linear relationship having a high determination coefficient is also established between block mean SVF and the facade density fraction, confirming the results of previous research. This formula and the optimized combinations for the OrbisGIS and the SAGA-GIS algorithms are finally used to calculate the SVF of every urban block of the Paris commune.
Highlights
IntroductionUrbanization is often characterized by a low vegetation density combined with a high fraction of impervious surfaces, a high rugosity (due to buildings’ size and height), and a denser energy consumption
Urbanization is often characterized by a low vegetation density combined with a high fraction of impervious surfaces, a high rugosity, and a denser energy consumption
The results of the analysis of sky view factor (SVF) calculation at point scale shows a slight advantage of the OrbisGIS algorithm (Table 4)
Summary
Urbanization is often characterized by a low vegetation density combined with a high fraction of impervious surfaces, a high rugosity (due to buildings’ size and height), and a denser energy consumption. These particular features affect the climate of the urban areas. The temperature is often higher in urban areas than in its surrounding rural areas This phenomenon is called Urban Heat Island (UHI) and may impact outdoor comfort [2], human health especially during heat waves [3], plant phenology [4], precipitation [5], energy consumption [6] and indirectly air pollution [7]. Several techniques have been investigated and tested all over the world: roof, facade and ground greening, roof and wall painting to alter the radiation absorption in both short and long-wave spectrum, water based solution such as fountains or sprinklers, building density and orientation optimization for shading purpose, etc. [9]
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