Urban Heat Risk and Human Health
Heat waves in central Europe are becoming more frequent and intense due to climate change (Ward et al., 2016). In cities like Zurich, factors like dense urban surfaces and building geometries can affect the formation of heat islands and increase heat stress for residents (Allegrini & Carmeliet, 2018). Shadow routes are therefore one possible adaptation strategy to improve comfort in public spaces.
Research Question
How can we identify the most shaded routes through the inner city of Zurich during hot summer days?
What are Heat Islands?
Urban areas store and release more heat than their rural surroundings (Gago et al., 2013), resulting in a phenomenon known as the Urban Heat Island effect. Almost every major city has one and they correlate with the size of the urban area, the bigger the city the more pronounced the heat island effect is (Parlow et al., 2013). Three primary factors cause the formation of heat islands in cities: Surface materials, lack of vegetation and urban geometry. Surface materials like concrete and asphalt absorb solar radiation well, store it, and slowly release it during the day and, especially, at night. A lack of vegetation causes less evapotranspiration, which usually has a significant cooling effect on the surrounding areas. Additionally, missing vegetation also results in missing shadows cast by trees and bushes. The urban geometry, the shape, orientations and height of buildings, play s nig role in urban heating and cooling effects. Tall buildings can trap heat between them and, depending on their orientation, reduce airflow in their surroundings (Wong et al., 2011). During the night, cities cool down more slowly compared to their rural outskirts. Nighttime heat strongly affects health and creates cumulative heat stress.
Who is affected by heat risk?
Since the heat island effect leads to higher temperatures in cities, especially during the summer, it often causes health related issues. Urban heat particularly affects elderly people, children, people with pre-existing health conditions, and residents of densely built-up neighbourhoods (Elmarakby & Elkadi, 2024). Heat stress can manifest in a variety of ways, which carries a multitude of adverse health effects for these at-risk groups. Elderly people, for example, can have a reduced capacity for heat regulation, while children commonly face higher risks of dehydration. Marginalized communities, who often are the residents of neighbourhoods with high building densities, are affected by the three factors above (Clark et al. 2024). Dense neighbourhoods exhibit more than average amounts of concrete and asphalt, often lack vegetation and greenspaces, and therefore offer less cooling opportunities to residents and pedestrians. Additionally, tall buildings can trap heat in the streets between them and reduce airflows that would contribute to cooling (Allegrini & Carmeliet, 2018).
Heat Risk = Exposure + Vulnerability
What can we do against it?
Cities can reduce heat stress through a range of urban adaptation strategies. Increasing the number of trees causes more shade which lowers direct exposure to the sun and improves thermal comfort for pedestrians. Nature-based solutions such as urban greenspaces and water features contribute to cooling through evapotranspiration, while reflective construction materials and cool roofs reduce heat absorption. In addition, climate-sensitive urban planning and improved airflow can help dissipate heat in densely built environments (Singh et al., 2024).
What is the situation in Zürich?
Zürich is increasingly affected by urban heat island effects. The city center is characterized by dense urban structures, sealed surfaces, and partly limited airflow. Some districts lack sufficient vegetation and shade coverage.
Our project links to the discussed heat island adaptation measures. We wish to find out which routes between any two points in the inner city of Zurich, offer the most shade to pedestrians
Why Shadow Routes?
Shadow routes are pedestrian paths designed to improve thermal comfort by maximizing shaded areas and reducing direct heat exposure. During heat waves, shaded routes can significantly lower radiant heat stress and make walking more comfortable and accessible. They also support public health by reducing the risk of heat-related illnesses and contribute to more equitable urban mobility, particularly for people who rely on walking or public transport during periods of extreme heat (Feng et al., 2024).
Thermal comfort is not only dependent on air temperature. Radiation, humidity, wind, and surface temperature also play a major role.
How is this conntected to the SDGs?
SDG 3: Good Health and Well-Being
This project contributes to SDG 3 by supporting healthier and safer mobility in urban environments. During periods of extreme heat, prolonged exposure to direct sunlight can increase the risk of heat stress and other health-related issues, especially for vulnerable groups such as elderly people or children. By identifying and recommending cooler, shaded walking routes, the application helps reduce heat exposure and promotes more comfortable and health-conscious pedestrian movement.
SDG 11: Sustainable Cities and Communities
The project aligns with SDG 11 by contributing to more climate-resilient and pedestrian-friendly cities. The interactive webmap highlights the importance of urban greenery, building structures, and shaded street networks in improving urban livability. By encouraging walkability and providing insights into thermally comfortable routes, the project supports sustainable urban planning and helps cities adapt to increasing temperatures caused by climate change.