An urban heat island is a local and temporary phenomenon experienced when certain pockets within a city experience higher heat load than surrounding or neighbouring areas on the same day. The variations are mainly due to heat remaining trapped within locations that often resemble concrete jungles. The temperature variation can range between 3 to 5 degrees Celsius.
Factors that contribute to it
- Rural areas have relatively larger green cover in the form of plantations, farmlands, forests and trees as compared to urban spaces. This green cover plays a major role in regulating heat in its surroundings. Transpiration is a natural way of heat regulation. This is the scientific process of roots absorbing water from the soil, storing it in the leaves and stems of plants, before processing it and releasing it in the form of water vapour.
- On the contrary, urban areas lack sufficient green cover or gardens and are often developed with highrise buildings, roads, parking spaces, pavements and transit routes for public transport. As a result, heat regulation is either completely absent or man-made.
- Proximity construction: An Urban Heat Island can be created when dwellings, stores, and industrial buildings are built close together. Building materials are often excellent at insulating and retaining heat. The regions around buildings become warmer as a result of this insulation.
- The heat island effect is exacerbated by waste heat from automobiles, industries, and air conditioners, which adds warmth to their surrounds.
- Engineers construct skyscrapers when there is no more space for an urban region to grow. Because of all of the building, waste heat and heat that escapes insulation have nowhere to go. It lingers in the UHI’s structures and between them.
- The cloud of air pollution that blankets many cities can operate as a small greenhouse layer, preventing outgoing thermal radiation (heat) from escaping.
- Black or any dark coloured object absorbs all wavelengths of light and converts them to heat, while white reflects it. Cities usually have buildings constructed with glass, bricks, cement and concrete — all of which are dark-coloured materials, meaning they attract and absorb higher heat content.
- Thus forms temporary islands within cities where the heat remains trapped. These are not the typical islands around water bodies, but urban heat islands that record higher day temperatures than other localities.
Impact on urban society
- Energy expenses: The urban heat island effect raises energy expenditures (for example, air conditioning), pollution levels, and heat–related sickness and death. Increased air-conditioning usage for cooling may contribute to global warming, which in turn leads to climate change.
- Heat-loving species colonisation: The UHI encourages the colonisation of species that like warm temperatures, such as lizards and geckos, due to increased temperatures in urban environments. Ectotherms are insects, like as ants, that are more common here than in rural settings.
- Heatwaves: Heat waves are common in cities, affecting human and animal health by causing heat cramps, sleep loss, and higher death rates.
- Poor air quality: Because more pollutants (from automobiles, industries, and people) are pushed into the air, air quality in UHIs is frequently poor. The urban landscape: buildings, roads, walkways, and parking lots prevent these toxins from dispersion and becoming less hazardous.
- Poor water quality: Water quality is also a problem. Warm water from the UHI flows into nearby streams, putting native animals that have acclimated to a colder aquatic habitat under stress.
How can urban heat islands be reduced?
- The main way to cut heat load within urban areas is increasing the green cover; filling open spaces with trees and plants.
- Green roofs: Using green roofs, which are plant-covered roofs of buildings, helps to cool things down. Using light-colored concrete (using limestone particles mixed with asphalt (or tar) to create a greyish or even pinkish road surface (as some locations in the US have done); they are 50% better than black because they absorb less heat and reflect more sunshine. We should also paint rooftops green and put solar panels against a green backdrop.
- Other ways of heat mitigation include appropriate choice of construction materials, promoting terrace and kitchen gardens, and painting white or light colours on terraces wherever possible to reflect heat.
How to structure
- Give a brief intro about urban heat islands
- Explain the major elements associated and how it is formed
- Analyse its impact on the urban society
- Suggest measures