As tropical cities heat up, this review reveals why parks, shade, heat advisories and smarter public messaging need to work together to protect the benefits of outdoor recreation without exposing vulnerable communities to unsafe humid heat.
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 around the world are turning to urban greening to harness the benefits of nature. Nature-based recreation in cities can promote physical and mental health, strengthen 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 dangerous to humans.
Public health recommendations can be seen as contradictory because they encourage outdoor recreation while also warning against heat exposure. Therefore, it is important to establish appropriate outdoor exposure levels in hot environments to distinguish between harmful heat stress and safe exposure. In the present review, researchers summarized evidence on outdoor recreation and wet heat stress in tropical cities and described adaptation strategies.
Rising urban heat in the tropics
Temperature extremes have increased in intensity and frequency worldwide due to increased greenhouse gas emissions, with urban warming further amplifying these trends. Increased heat from air conditioner use or transportation, building materials that retain more heat, surface sealing that reduces evapotranspiration and infiltration, and altered surface geometry lead to urban heating.
High temperature and humidity in tropical cities can lead to adverse health effects. While the contribution of humidity to heat-related health outcomes is debatable, there is consensus that increased heat stress can worsen population health. Many tropical cities are predicted to undergo rapid urbanization in the coming decades, with climate change expected to exacerbate heat hazards in humid, hot regions.
Populations in tropical urban areas face health vulnerability due to heat
Increasing heat stress means that tropical urban populations are often exposed to adverse climates. While the physiological limits of tolerance to extreme humidity and heat are unknown, it is recognized that higher humidity and temperature are associated with greater health risks. For example, high humidity and heat were associated with clinic visits and mortality in urban centers in Thailand.
In addition, heat-related health vulnerability varies widely within and between populations, with pregnant, infant and elderly populations and marginalized communities at increased risk. Vulnerable populations in urban areas with limited access to infrastructure and poorly ventilated homes are at 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 behavior in outdoor recreation
The authors found very limited evidence on how humid heat affects nature-based leisure behaviors in tropical cities. In a systematic review, they looked at 5,245 studies, but only five met the inclusion criteria.
Most available evidence was collected in Southeast Asia, including Indonesia, Malaysia and Singapore, with one study from Brazil. Together, these studies suggest that heat may influence the location, time, duration, and type of outdoor recreation undertaken. However, the evidence base remains limited by short study durations, narrow geographical scope and focus on a small number of green spaces.
Smart thermal responses for tropical cities
Research on mitigating urban heat stress has focused primarily on temperate regions, with evidence from tropical cities steadily increasing. In general, responses to heat hazards include limiting exposure and reducing heat hazards and vulnerability. Cities are increasingly designing best practices to reduce 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.
The types of vegetation, the structure and configuration, and the size of green spaces all affect the cooling potential of urban green spaces. Large green spaces often have the greatest cooling benefits, with effects that can extend to surrounding neighborhoods. Blue spaces can also reduce local temperatures, but to a lesser extent and only for 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 limiting outdoor activities, and the World Health Organization and other national health agencies recommend avoiding peak periods. Beyond behavioral measures, urban design strategies such as increased airflow and shading can reduce exposure.
In addition, continuous exposure to heat, such as playing in the shade and morning walks, may help otherwise healthy individuals acclimatize to heat and benefit from psychophysical and physiological adaptations. However, the authors emphasize that managed heat exposure should not be generalized to vulnerable groups, the elderly, occupational settings, or inadvertent exposure. Portable ventilation, cooling clothing and ice slush could reduce the heat. Fostering a smart heat culture, in which people understand both the benefits and risks of heat exposure, could reduce vulnerability amid increasing 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 the microclimate is crucial. Reducing unsafe heat exposure and promoting nature-based recreation require more comprehensive messages that connect general and heat health recommendations in culturally sensitive and inclusive ways.
Currently, heat advisories do not incorporate air pollution information, despite evidence of health impacts from air quality and heat. The review also highlights the need to avoid green gentrification, prioritize vulnerable communities and assess potential offsets, such as reflective surfaces that may impair pedestrian comfort or nighttime recreation that may raise safety and sleep concerns.
Overall, as tropical cities face increasing heat stress, ensuring safe and accessible nature-based recreation requires integrated approaches that balance ecological, social and technological issues.
