Describe the causes of the phenomenon of 'urban heat island'. What are the effective measures to deal with this phenomenon in India?

Causes of the Urban Heat Island Phenomenon

The formation and intensity of urban heat islands are driven by a combination of physical, environmental, and anthropogenic factors that fundamentally alter the energy balance of urban areas compared to natural landscapes.

1. Altered Land Surface Characteristics

• Replacement of Natural Vegetation: Urban development involves converting natural landscapes, rich in vegetation and water bodies, into impervious surfaces like concrete, asphalt, and buildings. Natural vegetation facilitates evapotranspiration, a cooling process where plants release water vapor. Its reduction removes this natural cooling mechanism.
• Low Albedo Materials: Urban surfaces, particularly roads and rooftops, are often constructed with dark materials (e.g., asphalt, conventional concrete) that have a low albedo, meaning they absorb a significant portion of incoming solar radiation rather than reflecting it. This absorbed heat is then slowly released, particularly at night, keeping urban areas warmer.
• High Heat Capacity: Building materials like concrete and brick possess high thermal mass (heat capacity), allowing them to absorb and store large amounts of heat during the day and release it slowly throughout the night, contributing to higher nighttime temperatures.

2. Urban Geometry and Morphology

• Urban Canyon Effect: The closely spaced tall buildings and narrow streets in dense urban areas create "urban canyons." These structures trap solar radiation and hinder the dissipation of heat and airflow. Multiple surfaces for reflection and absorption of sunlight increase the efficiency of heating in urban areas.
• Reduced Wind Flow: The complex geometry of tall buildings can obstruct natural wind patterns, reducing ventilation and preventing the dispersion of warm air and pollutants. This limited airflow inhibits convective cooling.
• Decreased Sky View Factor: Tall buildings and dense construction reduce the "sky view factor" – the amount of sky visible from a point on the ground. A lower sky view factor means less radiant heat can escape to the cooler upper atmosphere at night, trapping heat within the urban canopy.

3. Anthropogenic Heat Emissions

• Energy Consumption: Urban areas have high energy demands for air conditioning, heating, industrial processes, and lighting. The waste heat generated from these activities (e.g., HVAC systems, power plants) directly contributes to the warming of the urban atmosphere.
• Vehicular Emissions: A high concentration of vehicles in cities releases heat from engines and exhaust, adding to the ambient temperature. Traffic congestion exacerbates this issue.
• Industrial Activities: Industrial zones within or near cities are significant sources of waste heat, further intensifying the UHI effect in localized areas.

4. Air Pollution and Greenhouse Gases

• Atmospheric Pollution: High concentrations of pollutants and aerosols in urban air can trap outgoing longwave radiation, contributing to the greenhouse effect within the urban boundary layer and hindering atmospheric cooling.

Effective Measures to Deal with the Urban Heat Island Phenomenon in India

Mitigating the UHI effect in India requires a multi-pronged approach combining urban planning, architectural design, material science, and policy interventions.

1. Green Infrastructure Development

• Urban Forestry and Green Spaces: Increasing tree cover and developing parks, gardens, and green corridors in cities are crucial. Trees provide shade, reducing surface and ambient temperatures, and cool the air through evapotranspiration.
• Green Roofs and Walls: Implementing green roofs (rooftops covered with vegetation) and green walls (vertical gardens) on buildings can significantly reduce surface temperatures, provide insulation, and enhance evaporative cooling.
• Water Bodies and Features: Protecting and rejuvenating existing lakes, ponds, and rivers, and integrating new water features like fountains, can provide evaporative cooling and improve local microclimates.

2. Sustainable Building Materials and Design

• Cool Roofs: Promoting the use of reflective, light-colored materials or coatings on rooftops (cool roofs) can significantly increase solar reflectance and reduce heat absorption. These can lower indoor temperatures by 2-5°C and reduce energy consumption for cooling.
• Cool Pavements: Using reflective or permeable materials for roads, sidewalks, and parking lots can reduce surface temperatures. Permeable pavements also allow water infiltration, facilitating evaporative cooling.
• Energy-Efficient Building Design: Incorporating passive cooling techniques in architectural design, such as strategic shading, natural ventilation, appropriate orientation, and insulated walls, can minimize heat gain and reduce reliance on air conditioning.
• Use of Sustainable Building Materials: Utilizing insulated concrete forms, aerated concrete blocks, and eco-friendly bricks can reduce heat absorption and improve thermal comfort.

3. Urban Planning and Policy Interventions

• Integrated Urban Planning: Developing master plans that integrate climate resilience, prioritize green infrastructure, optimize urban geometry for ventilation, and control urban sprawl can effectively address UHI.
• Green Building Codes and Standards: Enforcing the Energy Conservation Building Code (ECBC) for commercial buildings and Eco Niwas Samhita for residential buildings, along with promoting green building rating systems (e.g., GRIHA, LEED-India), can mandate energy-efficient and heat-reducing construction practices. The National Building Code of India (NBC) also includes guidelines on efficient energy usage.
• Heat Action Plans (HAPs): Developing and implementing city-specific HAPs with early warning systems, public awareness campaigns, and provision of cooling centers is vital. Ahmedabad's HAP, for instance, includes cool roof initiatives.
• Reducing Anthropogenic Heat: Encouraging public transportation, promoting electric vehicles, and improving industrial energy efficiency can reduce waste heat emissions.
• Water Management: Implementing rainwater harvesting systems can store water for irrigation of green spaces, contributing to cooling and sustainable water resource management.

4. Research, Monitoring, and Awareness

• High-Resolution Monitoring: Developing advanced monitoring and forecasting capabilities for UHI at the ward level can help identify hotspots and tailor interventions.
• Public Awareness: Educating citizens about simple measures like using light-colored paints, planting trees, and efficient energy use can foster community participation in mitigation efforts.

India's commitment to climate action, reflected in initiatives like the India Cooling Action Plan (ICAP) and the Smart Cities Mission, provides a strong framework for addressing UHI. However, effective implementation, often requiring coordination between central, state, and local bodies, and tailored city-specific approaches, remains key.