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Why Cities Have Higher Temperature: Urban Heat Island (UHI)
Why Cities Have Higher Temperature: Urban Heat Island (UHI)

An urban heat island (UHI) is a phenomenon where urban areas experience significantly higher temperatures than surrounding rural areas due to the concentration of heat-absorbing surfaces, human activities, and urban infrastructure. The more population, higher use of vehicle and their exhaust and more industrial units that produces heat and green house that are main cause of heat in the urban areas. The urban area have less plants to absorb heat and caron dioxide produced from industries and vehicles on the road. This leads to a microclimate with elevated temperatures, often 1-3°C (1.8-5.4°F) higher than in nearby rural areas.
The rural has plain or irrigated with crops and trees that may release water vapor and absorbs heat, and heat can't retain in the plain or on watery areas.

Causes of Urban Heat Islands

Heat-absorbing surfaces

Dark-colored pavement, buildings, and roofs absorb solar radiation, heating up the surroundings. Urban areas have more populated buildings and congested buildings that retain more heat and get cities hotter than rural areas.

Urban canyons

Tall buildings and narrow streets create canyons that trap heat and reduce airflow. Cities should be made according to air flow and ventilation in homes or buildings to minimize heat retain and protect environment from higher temperature.

Vehicle emissions

Vehicles emit heat and pollutants, contributing to the UHI effect. According to some research the 40 percent of air pollution is due to vehicular emissions mainly in urban areas.

Industrial activities

Industrial processes, such as manufacturing and energy generation, release heat into the environment. Urban areas have more industries due to facilitation of raw materials and dispatch of products. Industrial units in urban area creates more heat and air pollutants to atmosphere that creates or helps to increase the urban heat island.

Population density

High population density leads to increased human activity, energy consumption, and waste heat generation. Higher pollution in urban areas are also creates more waste and pollution and low awareness to disposal of waste of homes and even in industrial units. Industries are bound through Environment department of state for proper disposal of waste either incinerated or recycled.

Lack of green spaces

Limited vegetation and green areas reduce the cooling effect of evapotranspiration. Urban areas have less space for plantation and irrigation of crops that also increase the heat.

Effects of Urban Heat Islands

Heat-related illnesses and mortality
Increased energy consumption and costs
Air pollution and poor air quality
Heat stress on urban infrastructure and buildings
Impacts on urban ecosystems and biodiversity
Economic and social disparities, as vulnerable populations are often more affected
Less life of building and materials
Disease due to air pollution like asthma and lungs problem

Mitigation strategies

Green infrastructure

Plant trees, green roofs, and urban gardens to increase evapotranspiration and shading. Every home and building should have green belt area for vegetation and plantation to reduce heat in urban areas.

Cool materials

Use light-colored, reflective materials for pavement, roofs, and buildings. That may reduces the less light absorbed on material and building. Dark colors absorbs more heat than lighter color shades.

Urban planning

Design cities with green spaces, parks, and public squares to reduce urban density. Every building should have green belt area and society or residential societies should have parks and play grounds to reduce heat absorption, and societies should be well ventilated.

Energy-efficient buildings

Implement energy-saving technologies and designs to reduce heat generation. Even all the appliances should be energy saving and buildings should be well ventilated.

Transportation

Promote public transportation, walking, and cycling to reduce vehicle emissions. Cycling is an important step to reduce vehicular emissions for long routes use of public transport is feasible. Government should increase the public transport and facilitate the public so they don't use separate or own vehicles.

Climate-sensitive urban design

Consider local climate conditions and heat island effects in urban planning and development. In the less developed countries no one is using this technology to save environment and reduce the heat by using climate sensitive building designs and maps.

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