(Slim) Shady - The relative role of buildings and trees in urban shade provision for pedestrians

Urban temperatures and heatwave frequency are rising, necessitating targeted adaptation measures such as shade provision. This study quantifies and compares building- and tree-generated shade along pedestrian walkways in 10 cities worldwide, from Stockholm (most northern) to Cape Town (most southern). We distinguish between grey and green shade at high spatial resolution and across temporal scales, offering a clearer understanding of their respective contributions to radiative cooling. Using high-resolution elevation data and aerial imagery, we model dynamic shade patterns across seasons and times of day. These are overlaid with sidewalk polygons from OpenStreetMap to conduct a city-scale, pedestrian-focused analysis. Results show that trees dominate shading at midday - when cooling is most needed - while buildings contribute more during morning and late afternoon, particularly in high-latitude urban canyons. Simulations indicate that tree presence can increase midday shade along pedestrian walkways by up to two orders of magnitude - for example, from near zero to about 10% in Rio de Janeiro, or more moderately, from 8% to 38% in Rome. In Amsterdam, tree shade alone elevates over 40% of sidewalks into a higher shade availability category, underscoring the transformative impact of green infrastructure. Our framework for quantifying green and grey shade highlights the importance of time-sensitive, spatially aware shade analysis in climate-resilient urban planning. All code and data processing workflows are open-source, supporting transparency, reproducibility, and future applications.