The expansion of the urban area, as well as the resulting big population, will necessitate a greater region. Rapid urbanisation will bring with it a slew of issues. Many cities, particularly megacities, are experiencing problems as a result of urbanization. In 2014, the United Nations reported that urbanisation is commonly considered to be on the rise. By 2050, cities are predicted to house 66% of the world’s population. Not only the process of the energy balance on urban surfaces but also the sea breeze system in large coastal cities could be affected by urbanisation. The phenomenon of Urban Heat Island (UHI) has grown as a result of urban sprawl.
Urban Heat Island (UHI) is a phenomenon in which hot surface air is concentrated in urban centres while surrounding temperatures in suburban/rural areas gradually decline. Warming the air above the surface (convection and radiation), evaporation of moisture, and heat storage in surface materials physically balance the energy absorbed by this urban surface system from solar radiation and generated by anthropogenic activity. The way this energy balance is partitioned determines the character of the urban climate, which influences how cities consume energy as well as residents’ comfort and well-being.
UHI is induced by a variety of causes that differ in urban and non-urban settings. The release of anthropogenic energy from air conditioning systems, energy emissions from industrial operations, motor vehicles, the ratio of mixed surfaces, and the differential in heat capacity of building materials with the natural structure are all examples of these elements. Most of the hotspots in urban areas were found on metal roofs, industrial buildings, warehouses, airport runways, railways, high-density parking lots, and solid waste disposal sites, according to Effat’s field verifications. Almost all hotspots have limited or no green space. The temperature on the ground could increase to 1.2°C.
Variations in albedo cause heat differences in various lands. Man-made objects, such as roads and houses, have a lower albedo and absorb more visible radiation than natural surfaces. The urban surface is generally hotter than the natural water-holding surface. Water evaporation releases energy from the surface and lowers the temperature. The urban surface swiftly releases water, in contrast to natural surfaces that may hold water, such as plants.
Heating and ventilation systems, industrial operations, and internal combustion engines are all examples of anthropogenic heat sources. As a result of energy usage, heat will be produced. According to Mather, because the heat capacity of asphalt and concrete is smaller than other types of surfaces, solar radiation falling on the created region (asphalt, concrete) causes the surrounding air temperature to rise.
As a result, the surface temperature and air temperature will be higher as the percentage of land area increases. The UHI effect is a type of urban heat accumulation phenomenon caused by human activities and urban building. It is often acknowledged as the most visible aspect of urban climate. Increased land surface temperatures caused by UHI will inevitably affect the flow of materials and energy in the urban ecological system, as well as altering its structure and function, resulting in several ecological and environmental effects on urban climates, urban hydrological situations, soil properties, atmospheric environments, biological habits, material cycles, and energy consumption. To understand the role of urban heat islands in urban-induced convection and precipitation, other relevant factors such as land-use changes between urban and surrounding areas must be explored.
The emergence of urban heat islands, increased cloudiness, fog, dust, precipitation, and the downwind urban heat plume, all while lowering humidity, are all climatic effects of urbanisation. Apart from these small-scale effects, activities occurring within city limits are the primary sources of greenhouse gases, primarily CO2 and fluorocarbons, which may have an impact on global climate and sea levels in the coming decades. The impact of varied urban forms on the urban microclimate and outdoor thermal effect is important. Massive building area, when compared to urban geometry, is not the primary factor influencing the urban microclimate. The average building height provided sufficient urban shade, which is a significant component that influences temperature value. Normally, courtyard building models provide higher outdoor thermal comfort, however, a simulation revealed that the distance between buildings matters more than the kind of building.
Adaptation and Mitigation: The constructed area is contributing to the increase in surface temperature, according to an analysis of land cover and land use overlaid with the surface temperature distribution. Due to the existence of this problem, greater urban development planning and a balance of economic, social, and ecological factors are required. The city’s long-term development is inextricably linked to its spatial planning. According to Biesbroek et al., the administrative method, which is linked to the geographical structure, is particularly successful in mitigating and adapting to climate change and warming. A comfortable and friendly urban environment will be created by spatial development planning, which regulates the increase of the built area and includes green open spaces.
Controlling the expansion in built-up land area and the development of tall buildings along the shore, as well as developing green and blue open spaces, are UHI adaptation methods. The construction of those spaces is prioritised in areas with high surface temperatures. The urban forest-shaped walkway, garden, or roof garden city can be constructed in areas where the spread and clustered form of the urban forest is not possible. Furthermore, the tree-dominated green space delivers the largest heat-stress suppressor when it is most required. The quantity and transport of cooling are affected by the size, spread, and shape of green spaces, with some huge isolated parks shown to offer the least amount of boundary layer cooling. Increased green space surface roughness contributes mostly to cooling at the urban-boundary layer climate scale, hence improving convection rather than evaporation efficiency. Even though blue space cooling and transport during the day can be significant, nocturnal warming is accentuated during the most severe situations. It is recommended that lower absorptivity, higher reflectivity, and bigger thermal conductivity materials be used to improve the thermal environment around buildings and decrease UHI. Apart from that, cool paint and roof ventilation can be used on the top-floor residential units. In a tropical climate, both are extremely energy efficient and cost-effective.
For pollution control boards and regional transportation plans, the climate is crucial; yet, small-scale climatic fluctuations are important for urban planners, landscape architects, and architects.
Reference:
- Ningrum Widya. 2018. Urban Heat Island towards Climate. Available from https://iopscience.iop.org/article/10.1088/1755-1315/118/1/012048/pdf
- Canan Cengiz. Urban Ecology. Available from https://www.intechopen.com/chapters/45413
