Urban Heat Island Effect
- UHI is an urban area which is significantly warmer than the surrounding rural areas.
- The temperature difference is more stark during the day hours and night. Weak winds reduces the heat transfer and makes this phenomena more apparent.
The main cause of UHI effect is the modification of land surfaces.
- Extensive concrete and asphalt surfaces, which absorb and retain heat from sun. These
materials have low albedo (reflectivity) and high heat capacity, leading to absorption and storage of solar radiation.
- Unscientific Urban Planning and Layout may also be responsible for UHI effect. Density of buildings, street patterns, and the arrangements of tall structures may affect the air flow and restrict the dissipation of heat.
- Decreased vegetation cover and reduction in agri fields: Vegetation help in regulating
temperature by a process of evatranspiration. In the absence of vegetation, this cooling effect reduces.
- Decrease in water bodies (like lakes and ponds) over the years reduce the cooling effect during summers.
- Increasing population also increase the human generated heat through refrigerators, ACs etc.
- UHI increases the probability of long duration heat waves and it also exacerbates the impact of heat waves.
- It leads to increased energy consumption. This is due to greater demand for cooling in hot weather conditions
- Elevated Emissions of Air Pollutants and Greenhouse Gases
- Increased energy consumption leads to more greenhouse gas emissions as more fossils will be burned for the energy.
- Fossil fuels also produce other harmful pollutants such as Sulphur dioxide, Nitrogen oxides, Particulate Matter, Carbon monoxide etc.
- The pollutants further result in formation of ground level ozone, acid rains etc.
- Ozone is formed when NOx reacts with Volatile Organic Compounds in presence of sunlight. If environment becomes hotter, more ground level ozone will be formed.
- It also decreases water quality as warmer waters put stress on the ecosystem.
- Storm water which gets warm will affect the nearby ponds, lakes and rivers too.
- Infrastructure Damage: The excessive heat in urban areas can cause damage to infrastructure, particularly roads, pavements and buildings.
- Some experts believe that it may be contributing to global warming.
Some positive impacts
- Lengthening the plant growing season in very cold regions.
How Urban Heat Island effect can be mitigated?
Proper Urban Planning – keep UHI effect in mind, while planning urban development.
- Lower building height, aligning streets against the sun’s path (i.e. in north-south direction) could prevent new layouts from heating up.
- Focus on energy efficient buildings which will ensure insulation, high-performance windows etc.
- Create monitoring systems to automatically identify UHIs.
- It includes Green Roofs (Roof partially or completely covered by vegetation)
- Painting house in light colors
- Promoting urban forestry (For e.g. use Miyawaki method)
Protect Water Bodies and Permeable Surface:
- This will ensure high soil moisture and proper cooling of cities.
Community Engagement and Education
- Promoting behavioral changes like reducing energy consumption, planting more trees, etc.
- Promote collaboration between various stakeholders like state government, local bodies, NGOs etc.
▫ These measures can not only help mitigate UHI effect, but can also improve urban resilience, enhance public health and create sustainable and livable cities.
i. What is Urban Heat Island? What are the key factors responsible for the phenomena. [150 words, 10 marks]
ii. “Urban Heat Island effect is accentuated by rapid urbanization”. Elaborate. Suggest some measures to deal with the phenomena. [200 words, 12.5 marks]