Urban Heat Island - Rau's IAS

Context: Carbon Brief analysis revealed nearly 40% of the Earth hit its highest-ever daily temperature between 2013 to 2023.

About Urban Heat Island (UHI)

An urban heat island refers to a phenomenon where urban areas experience significantly higher temperatures compared to surrounding rural areas.

Global Cases of rising temperature:

The United Kingdom crossed 40 degrees Celsius for the first time ever in July 2022.
A small town in China’s northwest recorded 52-degree Celsius last year, the highest ever for that country.
In 2021, Sicily in Italy recorded 48.8 degree Celsius, the highest for Europe ever.
Recent temperatures in New Delhi, notably a reported 52.9°C, raise concerns, pending verification. Doubts arise due to inconsistencies with other stations, with Safdarjung recording 46.8°C, an 80-year high.

The sun’s heat and light reach the city and the adjoining rural areas in the same way.
The difference in temperature between urban and less-developed rural areas has to do with how well the surfaces in each environment absorb and hold heat.
If you travel to a rural area, you’ll probably find that most of the region is covered with plants grasses, trees, and farmland.
Plants take up water from the ground through their roots and store the water in their stems and leaves. The water eventually travels to small holes on the underside of leaves.
There, the liquid water turns into water vapor and is released into the air. This process is called transpiration. It acts as nature’s air conditioner.

Development Process:

Daytime: During the day, urban surfaces absorb solar radiation, heating up and raising local temperatures. Buildings and structures trap heat, creating thermal energy reservoirs.
Nighttime: Urban areas release stored heat slowly, resulting in elevated nighttime temperatures compared to surrounding rural areas. This phenomenon is known as the "urban heat island effect.

Human Activities: Urbanization leads to the creation of structures such as buildings, roads, and pavements, which absorb and retain heat.
Urban Canyon effect: The tall buildings within many urban areas provide multiple surfaces for the reflection and absorption of sunlight, increasing the efficiency with which urban areas are heated.
Modification of Land Surface: Urban development alters the land surface through the removal of vegetation, which reduces evaporative cooling and increases heat absorption.
Anthropogenic Heat: Activities like transportation, industrial processes, and energy consumption release heat, contributing to elevated temperatures.

Albedo Effect: Urban surfaces, such as concrete and asphalt, have lower albedo (reflectivity), absorbing more solar radiation and increasing temperatures.
Limited Green Spaces: The reduction of green spaces like parks and gardens decreases the cooling effect of vegetation and exacerbates heat retention.

Factors Influencing UHI Intensity:

Urban Morphology: The layout, density, and height of buildings influence UHI intensity. Compact urban areas with tall buildings tend to trap more heat.
Climate: Local climatic conditions, such as wind patterns and humidity, can affect the intensity of UHI.
Urban Design: Factors like street orientation, building materials, and green infrastructure can either exacerbate or mitigate UHI effects.

Impact of UHI:

Health Risks: Higher temperatures in urban areas can lead to heat-related illnesses and exacerbate air pollution, affecting public health.
- Urban Heat Islands (UHIs) exacerbate heat waves, increasing heat-related illnesses and fatalities.
- Heat exposure correlated with mental health issues and decreased academic performance.
- UHIs worsen air quality, accelerating pollutants' production and impacting health.
Energy Consumption: Increased cooling demands in urban areas result in higher energy consumption and associated greenhouse gas emissions.
Ecological Effects: UHI can disrupt ecosystems, alter local climate patterns, and affect biodiversity.
- Urban Heat Islands (UHIs) raise water temperatures, harming aquatic ecosystems.
- Rapid temperature changes due to UHIs stress aquatic life, causing fish kills.
- UHIs alter breeding strategies and habitat ranges of species.
Social Impacts: Vulnerable populations, such as the elderly and low-income communities, are disproportionately affected by UHI, exacerbating social inequalities.
- According to a study by the International Labour Organization (ILO), in 1995, the working hours lost in India due to heat stress were 5.87 per cent in agriculture and construction, 2.95 per cent in industry, and 0.63 per cent in services.
- These numbers are anticipated to increase to 9.04 per cent in agriculture and construction, 5.29 per cent in industry, and 1.48 per cent in services by 2030.

Green Infrastructure: Increasing vegetation cover through parks, green roofs, and tree planting helps mitigate UHI effects by providing shade and enhancing evaporative cooling.
Urban Planning: Designing urban spaces to prioritize pedestrian-friendly environments, incorporating green spaces, and promoting sustainable building practices can reduce UHI intensity.
Cool Roofing and Materials: Using reflective roofing materials and heat-absorbing coatings on pavements can lower surface temperatures and mitigate heat absorption.
Heat Island Reduction Programs: Implementing policies and initiatives focused on reducing urban heat island effects, such as urban forestry programs and building codes promoting energy-efficient designs.