How Street Trees and Urban Plants Reduce Harmful UV Rays

Jim Crocker
28th June, 2024

How Street Trees and Urban Plants Reduce Harmful UV Rays

Image Source: Natural Science News, 2024

Key Findings

  • The study, conducted in Brisbane, shows that tree shade can reduce midday UV index (UVI) by up to 91% compared to an unobstructed sky
  • Specific tree species like Pongamia pinnata and Xanthostemon chrysanthus are particularly effective in reducing UVI
  • Planting and maintaining these trees can enhance UV protection and improve walkability in urban areas
Urban environments, especially in hot-humid climates, pose significant challenges to walkability and personal sun exposure, impacting quality of life and health. Recent research by the University of Southern Queensland[1] delves into the role of tree shade in mitigating harmful ultraviolet radiation (UVR) and influencing the maximum daily UV index (UVI). The study evaluates the seasonal impact of tree shade on UVI by analyzing 210 hemispherical sky view images taken along public walkways in 10 residential suburbs of Brisbane. Tree shade, particularly during peak midday solar exposure, can significantly reduce UVR. The research highlights that the presence of tree canopies can reduce midday UVI by up to 91% compared to an unobstructed sky. The study's findings are crucial in understanding how urban planning and tree maintenance can enhance UV protection for residents. Specific tree species such as Pongamia pinnata, Xanthostemon chrysanthus, Senna siamea, and Libidibia ferrea are identified as particularly effective in reducing UVI. By planting and maintaining these species, urban areas can improve their shade characteristics and provide better UV protection. This research builds on earlier studies that emphasize the importance of outdoor space and walkability in urban environments. For instance, a study investigated the microclimatic functions of an overhead structure in improving walkability in hot-humid climates[2]. It found that shaded zones significantly reduce solar radiation and improve thermal comfort, which can influence pedestrian behavior. The new study complements these findings by demonstrating how natural shade from trees can also enhance walkability and UV protection. Moreover, the study's focus on UVR aligns with previous research on personal sun exposure risks in urban environments. A study using polysulphone film (PSF) to measure daily solar UVR exposure in urban canyons found significant variations depending on the sky view factor and orientation to the sun[3]. The new study extends this understanding by showing how tree shade can mitigate these risks in residential areas. The importance of reducing UV exposure is underscored by research on skin cancer prevention. A Sunscreen Summit in Australia and New Zealand recommended daily sunscreen use when the UV index is forecast to reach three or greater, highlighting the need for comprehensive sun protection measures[4]. The new study provides an additional strategy by emphasizing the role of tree shade in reducing UV exposure, potentially decreasing the incidence of skin cancer. Despite the widespread adoption of the UV index to raise awareness about skin protection, studies have shown that comprehension and use of the UVI for sun safety behaviors are often low[5]. The new study contributes to this body of knowledge by providing practical insights into how urban planning and tree maintenance can naturally reduce UV exposure, complementing public health campaigns. In summary, the research by the University of Southern Queensland demonstrates the significant impact of tree shade on reducing UV exposure in urban environments. By identifying effective tree species and emphasizing the importance of planting and maintaining these trees, the study offers practical solutions for enhancing UV protection and walkability in residential areas. This research, along with previous studies, highlights the multifaceted approach needed to address urban environmental challenges and improve public health.

EnvironmentSustainabilityPlant Science


Main Study

1) The mitigating effect of street trees, urban flora, and the suburban environment on seasonal peak UV indices: A case study from Brisbane, Australia.

Published 26th June, 2024

Related Studies

2) Improving street walkability: Biometeorological assessment of artificial-partial shade structures in summer sunny conditions.

3) A Comparison of Solar Ultraviolet Radiation Exposure in Urban Canyons in Venice, Italy and Johannesburg, South Africa.

4) When to apply sunscreen: a consensus statement for Australia and New Zealand.

5) Awareness, understanding, use, and impact of the UV index: A systematic review of over two decades of international research.

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