Urban geometry parameters as indicators for urbanization effects: A case study in Paranhos, Portugal

Abstract

This urban climate study is about the parish of Paranhos - Porto, Portugal. The size of the parish area is approximately 7,2 km2. The area grew substantially in the last fifty years both in terms of population number, widening of the urbanized area and extent of human activities as a result largely of the creation of a new University Pole. We have tried to evaluate the influence of the urban geometry of Paranhos as an external cause of the climatic subsystem, generating important contributions to changes in the behavior of temperature (thermal anomalies). The methodology is based on on statistical analyses of measured urban-rural temperature anomalies (u-r) versus two parameters characterizing the urban structure, namely: Street geometry is parameterized by a 2-dimensional view factor (vf) representing the unobscured angular fraction of sky in a vertical plane perpendicular to the street. This approach differs from the 3-dimensional sky view factor (Oke 1987). Building density (bd) is parameterized by the number of buildings (n) in square areas of 100 × 100m, (n/hm2). The correlations established separately between street geometry and building density respectively and the thermal deviations show that both parameters are of significance as explanatory factors for the urban heat island. The most densely built up areas with lowest vf correspond to the areas where the urban heat island is best developed and observed most often.