How heat-smart cities can protect outdoor recreation in a warming world

Review: The future of nature-based recreation in warming tropical cities. Image Credit: taka1022 / Shutterstock

A recent review article published in the journal npj Urban Sustainability reviewed evidence on outdoor recreation and humid heat stress in tropical cities.

Cities worldwide are shifting toward urban greening to harness nature's benefits. Nature-based recreation in cities can promote physical and mental health, enhance community resilience, and strengthen social cohesion. However, outdoor recreation in tropical cities often means exposure to hot, humid conditions that are thermally uncomfortable, which, in extreme cases, can even be unsafe for humans.

Public health recommendations may be perceived as conflicting because they encourage outdoor recreation while also warning against heat exposure. Therefore, it is crucial to determine the appropriate outdoor exposure levels in hot environments to differentiate between harmful heat stress and safe exposure. In the present review, researchers summarized evidence on outdoor recreation and humid heat stress in tropical cities and outlined adaptation strategies.

Rise in urban heat in tropical regions

Extreme temperatures have increased in intensity and frequency worldwide due to elevated greenhouse gas emissions, with urban warming further amplifying these trends. Increased heat from air conditioning use or transportation, construction materials that retain more heat, surface sealing that reduces evapotranspiration and infiltration, and altered surface geometry all drive urban warming.

High temperature and humidity in tropical cities can lead to adverse health outcomes. While the contribution of humidity to heat-related health outcomes is debatable, there is consensus that increased heat stress may deteriorate population health. Many tropical cities are projected to undergo rapid urbanization over the coming decades, with climate change expected to worsen heat hazards in humid, hot regions.

Tropical urban populations face heat health vulnerability

The increase in heat stress means tropical urban populations are often exposed to adverse climates. While the physiological limits of tolerance to extreme humidity and heat are unknown, it is acknowledged that higher humidity and temperature are associated with greater health risks. For instance, high humidity and heat were correlated with clinic visits and mortality in urban centers in Thailand.

Moreover, heat-related health vulnerability varies widely within and between populations, with pregnant, infant, and older populations and marginalized communities facing an increased risk. Susceptible populations in urban areas with limited access to infrastructure and poorly ventilated homes are at a much higher risk of heat exposure. Poor air quality, combined with high humidity and high temperatures, can increase the risk of urban mortality.

Limited evidence on outdoor recreation behavior

The authors found very limited evidence on how humid heat affects nature-based recreation behaviors in tropical cities. In a systematic review, they screened 5,245 studies, but only five met the inclusion criteria.

Most available evidence was concentrated in Southeast Asia, including Indonesia, Malaysia, and Singapore, with one study from Brazil. Together, these studies suggest that heat can influence the location, timing, duration, and type of outdoor recreation undertaken. However, the evidence base remains limited by short study durations, narrow geographic scope, and a focus on a small number of green spaces.

Heat-smart responses for tropical cities

Research on mitigating urban heat stress has primarily focused on temperate regions, with evidence from tropical cities steadily growing. In general, responses to heat risks involve limiting exposure and reducing heat hazards and vulnerability. Cities are increasingly planning best practices to decrease heat hazards, such as urban forests, vertical greenery, parks, and street trees. The review draws on Singapore-specific examples, including Cooling Singapore 2.0 and the national Heat Stress Advisory, to illustrate emerging heat-smart approaches.

Vegetation species, structure, and the configuration and size of green spaces all influence urban greenery’s cooling potential. Large green spaces often have the greatest cooling benefits, with effects that can extend into surrounding neighborhoods. Blue spaces can also reduce local temperatures, but to a lesser extent and for only a limited period of the day. Urban temperatures could also be reduced by modifying urban forms, such as urban geometry and shading.

Spatially refined and socially relevant heat health advisories can limit population exposure to heat hazards. For example, the National Heat Stress Advisory in Singapore advises moderating outdoor activities, and the World Health Organization and other national health bodies recommend avoiding peak-heat periods. Beyond behavioral measures, urban design strategies like increased airflow and shading can reduce exposure.

Furthermore, consistent exposure to heat, such as shaded outdoor play and early-morning walks, may help otherwise healthy people to acclimate to heat and benefit from psychophysical and physiological adaptations. However, the authors emphasize that managed heat exposure should not be generalized to vulnerable groups, older adults, occupational settings, or involuntary exposure. Portable ventilation, cooling garments, and ice slushies could reduce heat illness. Fostering a heat-smart culture, in which people understand both the benefits and risks of heat exposure, could decrease vulnerability amid rising environmental challenges.

Concluding remarks

Maximizing heat mitigation responses requires addressing several key knowledge gaps. First, an improved understanding of how urban form and green and blue spaces affect microclimate is crucial. Reducing unsafe heat exposure and promoting nature-based recreation require more integrated messaging that links general and heat-health recommendations in culturally sensitive, inclusive ways.

Currently, heat advisories do not incorporate air pollution information, despite evidence of health implications of air quality and heat. The review also highlights the need to avoid green gentrification, prioritize vulnerable communities, and assess potential trade-offs, such as reflective surfaces that may worsen pedestrian comfort or nighttime recreation that may raise safety and sleep-related concerns.

Overall, as tropical cities face intensifying heat stress, ensuring safe and accessible nature-based recreation requires integrated approaches that balance ecological, social, and technological considerations.

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