Neighbourhood morphology and solar irradiance in relation to urban climate
Assessing the relationship between neighbourhood morphology and urban climate is becoming increasingly important as cities continue to grow and the climate continues to change. Here we focus on the impact of (1) shapes and sizes of buildings, (2) street layouts, and (3) spatial distributions of buildings and streets on the urban climate in the 16 neighbourhoods (zones) within the city of Geneva, Switzerland. The results show that the size distributions of the areas, perimeters, and volumes of the buildings follow approximately power laws, whereas the heights of the buildings follow a bimodal (two-peak) distribution. Using the Gibbs-Shannon entropy formula as a measure of dispersion (spreading), we calculate the area, perimeter, volume, and height entropies for the 16 neighbourhoods in Geneva and show that the entropies have strong positive correlations (R2 = 0.43-0.84) with the average values of these parameters. By contrast, there are negative correlations (R2 = 0.39-0.54) between building density or urban compactness (site coverage and volume-area ratio) and the entropies of building areas, perimeters, and volumes. The calculated length-size distributions of the streets show negative correlations (R2 = 0.70-0.76) with the number of streets per unit area as well as with the total street length per unit area. We compare the neighborhood morphologies with the annual and monthly solar irradiance for each of the 16 neighborhoods using the simulation tool CitySim. The results show a negative correlation between building densities and solar irradiation as well as between street densities and solar irradiation. By contrast there is a positive correlation between entropy of the street lengths and solar irradiation, indicating that the greater the variation in street length the greater the solar irradiation. Further work will include comparison of these results with the average surface temperatures, sky view factors, and daylight factors in the 16 neighborhoods so as to explore the relations between neighborhood morphology and the local climate and, thereby, providing quantitative information to help urban designers in the decision making processes.