Improving the Climate Resilience of Urban Road Networks: A Simulation of Microclimate and Air Quality Interventions in a Typology of Streets in Thessaloniki Historic Centre

Abstract

The improvement of the urban microclimate in the densely-built central areas of Mediterranean cities should be a key objective of integrated urban and transport planning and design in accordance with the UN Sustainable Development Goals on energy, sustainable cities, and climate action. The urban climate of cities in warm regions, already burdened by the urban heat island effect, is expected to worsen further due to the global climate crisis. This study investigates the performance of common environmental street design strategies on microclimate, thermal comfort, and air quality under extreme heat conditions in the Mediterranean city of Thessaloniki, Greece. A typology of streets was selected using criteria such as road functional classification and orientation, land uses, building height/street width ratio, the sky view factor, and the continuity/discontinuity of buildings. A conservative scenario (use of cool/photocatalytic and porous materials for sidewalks, lighter pavements, additional tree planting, installations of green roofs) and a radical scenario (pedestrianization and total traffic prohibition) of environmental design interventions were simulated using the ENVI-met 5.1 software. The research findings demonstrated that the car-free interventions combined with the use of environmentally friendly materials in the public realm could significantly reduce the heat island effect and mitigate gaseous pollutants. The perceived air temperature (Physiological Equivalent Temperature—PET index) can decrease by up to 15 °C in well-shaded locations and near building corners, while nitrogen oxides can be reduced by up to 87% when considering a more radical pedestrianization scenario. The standardization of environmental interventions following a typology of urban streets could support planners and decision-makers in detecting the appropriate solutions for improving the urban microclimate.

On the Role of Urban Mobility Layout against Urban Microclimate. The Case Study of Turin, Italy

“…-Urban policies should further promote pedestrianization of car-centered streets as an effective way to provide space for implementing UHI mitigation and climate adaptation strategies [28,30]. Removal of vehicular traffic improves safety, promotes human-centered approach and enhances the quality of life [31].…”

“…This model is in contrast with a growing and urgent need for "soft mobility", i.e., zero-emission mobility centered on pedestrian, biking and transit infrastructure. Indeed, designing for hard mobility intensifies the UHI effect through additional heat fluxes from vehicles and overheated urban surfaces, resulting in higher heat stress and health risks for pedestrians [28]. On the contrary, reducing hard mobility spaces has been proven to decrease the amount of traffic in the examples of San Francisco; Portland, Oregon; Milwaukee, Wisconsin; Seoul, South Korea [29].…”

“…On the contrary, reducing hard mobility spaces has been proven to decrease the amount of traffic in the examples of San Francisco; Portland, Oregon; Milwaukee, Wisconsin; Seoul, South Korea [29]. Furthermore, research has shown that the transition from hard to soft mobility allows for the implementation of different mitigation strategies, resulting in the improvement of thermal conditions [28,30]. Indeed, promoting policies for boosting pedestrianization and walkability is one of the most effective strategies for developing mobility oriented towards humans and climate friendliness [31].…”