Urban heat and air pollution in the built environment are interlinked and contribute to increased negative health impacts among urban dwellers. Sharon Onyango highlights the connection between these three factors within the transport sector developments in Africa, providing various urban planning strategies for mitigation to improve human health and wellbeing.
Sub-Saharan Africa (SSA) is considered among the rapidly growing regions, with an urban annual growth rate of approximately 3.5 per cent. Urban sprawl in SSA has posed downsides to the achievement of the Sustainable Development Goals (SDGs), particularly SDGs 3 and 11. The significant driver of urban sprawl in SSA is uncontrolled urban developments from the surging population, with a high demand for built infrastructure. The instantaneous urbanisation process in SSA has led to the modification of urban biophysical features, characterised by building constructions, intensive mobility and transport corridors, and paved surfaces. These surfaces are impervious and absorb solar radiation due to low reflectance, creating ‘heat islands’ with slightly warmer temperatures compared to their surrounding peri-urban and rural areas.
Besides the construction material, Urban Heat Islands (UHI) are influenced by the urban built environment’s physical features, such as their height, compactness, and organisation. Even so, in Africa, UHI-related research remains scarce. Similarly, infrastructure development continues to stimulate urban air pollution (AP) in most African cities. The common pollutants responsible for urban AP include Nitrogen Dioxide, particulate matter (PM2.5 & PM10), Carbon Monoxides, Sulphur Dioxide and Volatile Organic compounds. These are attributed to vehicular emissions, industries, waste combustion, heating of buildings, and other anthropogenic activities.
UHI and AP Risks to Health and Thermal Comfort
UHI and AP in SSA urban areas create considerable impacts on the health and well-being of city dwellers. Studies have revealed that UHI effect is present in African cities despite exhibiting a higher green space to paved surface ratio. Transport-linked urban expansion accounts for a greater proportion of UHI effects and poor air quality. In extreme cases, UHI can cause heat waves and a reduction of human thermal comfort. Heat stress increases cardiovascular and respiratory failures, kidney damage from dehydration, and heat strokes with more hospital admissions. Correspondingly, UHI accelerates the effects of AP by increasing pollutant levels through air turbulence. In turn, this affects human health, leading to premature deaths commonly induced by respiratory infections and diseases. These mortalities are significantly higher among vulnerable urban communities, including persons with pre-existing conditions, children, and the elderly.
UHI and AP Management and Mitigation Strategies
Diverse mitigation strategies to minimise the UHI effects and AP impacts have been explored and found worthwhile in reducing related health risks.
- Urban Green Spaces (UGS) and Cool Infrastructure: UGS and cool infrastructures such as walls, roofs, and pavements act as carbon and heat sinks within the urban environment, improving public health risk exposure. A recent study in Nairobi presented higher heat stress in an urban street compared to an urban park using the Physiological Equivalent Temperature (PET) heat index. Incorporating greenery, based on its canopy form and species, within the built environment can potentially improve thermal comfort and absorb air pollutants like carbon.
- Construction Design and Material: Both the material and design of the buildings are key in countering the effect of UHI and air pollution. Using materials that have high radiation reflectance reduces UHI, while pollution absorption materials can filter pollutants, improving air quality.
- Policies for AP and UHI Mitigation: Integrating both urban planning practices and public health policies while cooperating with other sectors to establish policies is essential in reducing vulnerability. In 2022, Nairobi City County passed an Air Quality Bill alongside a Climate Action Plan for 2020-2050. Local governments in African cities should ensure appropriate implementation of these policies while creating public awareness to address both UHI and AP.
- Decarbonising Automotives: Contemporary technologically designed electric and hydrogen-cell vehicles have shown a decrease in pollution from vehicular emissions. Adoption of these vehicles by African Cities can improve the urban air quality, public health, and environmental sustainability significantly.
- AP Monitoring along Mobility Corridors: Outdoor AP sensors should be integrated into the Intelligent Transport Systems (ITS), ensuring that human exposure to vehicular emissions stays within the permitted limits. Tracking pollution levels along the roads is possible through web-based air quality software linked to the monitors.
Resilience Planning to Reduce UHI effects and AP impacts
To make cities more habitable, different planning concepts have been established to promote resilience and sustainability. Smart Growth concept encourages sustainable neighbourhoods, while New Urbanism and Transit-Oriented Development (TOD) concepts foster sustainable architectural and transport developments. All these planning concepts encourage walkability and minimal reliance on automobiles, promoting good health and well-being within the cities.
In African cities, urban planners should consolidate these concepts in land use planning, urban design, greening, and anthropogenic heat reduction for existing and new urban developments. However, since the mitigation approaches are naturally long-term, built environment heat resilience transformation may take time. Therefore, it is paramount for African cities to implement these strategies promptly. Further citizen science and empirical research interlinking urban development, UHI, AP, and local climate change is still encouraged for proper interventions to achieve SDGs 3 and 11 in African cities.