3D Solar Analysis of the Street Network and Impact Estimation of the Shade of Trees at the District Scale

Abstract. Trees on city streets are the valuable resource for the pedestrian comfort and mitigation of effects of the urban heat island. Solar studies at the city and district scales can be conducted in 3D using various tools. However, 3D city models often lack the geometry of high vegetation in solar analysis, as tree representation is more complex compared to buildings. While this omission is not critical for the assessment of rooftops, shading from trees significantly affects pedestrian comfort on the street in the summer, building-integrated photovoltaics on façades, and energy consumption of buildings. This paper presents a 3D solar analysis that integrates trees into studies at the district scale using a widely adopted 3D raytracing algorithm. The study area covers 9.24 km², evaluating 1,056,482 faces and incorporating 34,617 trees. Tree transmissivity is accounted for with separate calculations and post-processing of the output datasets. The study demonstrated up to a 30% decrease in solar radiation on streets compared to analysis that excludes trees, as well as an 18% increase in solar access to street surfaces compared to raster-based calculations in GIS. The resulting analytical datasets are integrated into the Urban Digital Twin of Sofia using open standards such as CityGML and 3D Tiles. CityGML Vegetation ADE is reviewed to incorporate the proposed workflow. This approach offers a straightforward solution for assessing the impact of tree shade with modest computation time and can be scaled to the city level in future research.