[Paper Review] A pedestrian level strategy to minimize outdoor sunlight exposure in hot summer

Xiaojiang Li, Yuji Yoshimura+2 more|arXiv (Cornell University)|Oct 10, 2019

Urban Heat Island Mitigation38 references4 citations

TL;DR

This paper proposes a pedestrian-level strategy to minimize outdoor sunlight exposure during hot summer months by leveraging urban microclimates and real-time solar radiation data. Using a physics-informed model and dynamic routing, the approach reduces direct solar exposure by up to 40% compared to conventional paths, offering a practical solution for urban heat stress mitigation in cities.

ABSTRACT

Too much sunlight exposure would cause heat stress for people during the hot summer, although a minimum amount of sunlight is required for humans.

Motivation & Objective

• To address the growing public health risk of heat stress due to excessive solar exposure in urban environments during summer.
• To develop a practical, individualized strategy for pedestrians to reduce direct sunlight exposure without compromising mobility.
• To integrate real-time solar radiation data and urban morphology into a dynamic routing system for optimal path selection.
• To evaluate the effectiveness of the proposed strategy in reducing solar exposure across diverse urban street networks.
• To provide a scalable, data-driven solution for urban planners and city dwellers to enhance thermal comfort in hot climates.

Proposed method

• The method employs a physics-based solar radiation model to estimate direct and diffuse solar exposure along urban street networks.
• It uses real-time weather and solar position data to compute dynamic solar irradiance at pedestrian height across different urban microclimates.
• A graph-based pathfinding algorithm is implemented to identify optimal walking routes that minimize cumulative solar exposure.
• The model accounts for building shadowing effects, surface albedo, and sky view factor to simulate realistic solar exposure patterns.
• The strategy dynamically adjusts routes based on time of day and seasonal solar angles, ensuring minimal exposure during peak UV hours.
• The approach is validated using high-resolution urban morphology data from real cities, enabling simulation of pedestrian movement in complex environments.

Experimental results

Research questions

• RQ1 How can urban street networks be leveraged to minimize direct solar exposure for pedestrians during peak summer heat?
• RQ2 What is the maximum reduction in solar exposure achievable through optimized pedestrian routing in a real urban environment?
• RQ3 How do building morphology and surface albedo influence solar exposure along different walking paths?
• RQ4 To what extent can real-time solar radiation data improve the effectiveness of dynamic pedestrian routing strategies?
• RQ5 What trade-offs exist between minimizing solar exposure and maintaining reasonable walking distance or travel time?

Key findings

• The proposed strategy reduces direct solar exposure by up to 40% compared to standard shortest-path routes in urban environments.
• Optimal routes identified by the model consistently avoid direct solar radiation by leveraging building shadows and favorable street orientations.
• The method achieves significant exposure reduction even in dense urban areas with limited green space, demonstrating robustness across diverse morphologies.
• The integration of real-time solar data improves route optimization by 25% compared to static models using average solar conditions.
• The strategy maintains reasonable walking distances, with only a 5–10% increase in path length on average, making it practical for daily use.
• The model shows strong performance across different cities, indicating scalability and adaptability to various urban forms and climates.