Follow the shade: detection of optimally shaded pedestrian paths within the historic city center of Thessaloniki

Abstract

Both the EU Green Deal and the UN SDGs consider the transition to sustainable urban mobility a key priority. Designing cities and public spaces to accommodate pedestrians and not cars has been a core strategy of sustainable urban mobility since the 1990s. Yet, the quality of pedestrian traffic is highly dependent on outdoor meteorological conditions which may encourage or discourage walking. The ongoing global climate change and the local Urban Heat Island (UHI) effect have a combined adverse effect on pedestrian heat stress and associated health risks. Increased heat stress is a significant disincentive to walking and can threaten urban life, especially during summer in hot climates, such as the Mediterranean. Humans have the capacity to adapt to hot weather through physiological responses and changes in clothing, activity and behavior. Pedestrians walking during a hot day will likely pick a comfortable route, i.e. one that it is shaded and easily traversable. This is identified visually at the street level, which makes planning longer comfortable routes in the urban environment a challenging task. The paper presents an easily reproducible methodology for generating optimal pedestrian paths with respect to shading and terrain slope. The methodology is applied on the historic city center of Thessaloniki, Greece. The study utilizes QGIS and the UMEP plugin to generate time series of urban shadow raster data and then calculate the least cost path from any starting point to any destination within the city center. The results are then compared to routes generated by conventional shortest path algorithms.