Source: TOI

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Context :

Recently, Telangana Socio Economic Outlook 2025 report was published.

It said that Hyderabad is facing increased nighttime heat stress because of the Urban Heat Island (UHI) effect.

What is the Urban Heat Island (UHI) effect ?

• Urban Heat Island (UHI) is a phenomenon where cities experience significantly higher temperatures than the surrounding rural areas.
• This temperature difference happens due to how urban surfaces absorb & retain heat compared to rural areas.

Why Does UHI Happen?

• While the sun heat & light reach both cities & rural areas similarly.
• But the difference in temperature comes from how each environment absorbs & holds that heat:
• Rural Areas: These areas are generally covered with plants, trees, grasses, & farmland. Plants absorb water from the ground through their roots & release it through transpiration (evaporation from leaves). This process cools the air naturally.
• Urban Areas: In contrast, urban areas are densely built with concrete, asphalt, & buildings that absorb more heat. So It is leading to higher temperatures.

Development Process of UHI:

1. Daytime: During the day urban surfaces (like roads & buildings) absorb solar radiation, storing thermal energy & raising local temperatures.
2. Nighttime: The heat stored in urban areas is released slowly at night. So it  results in elevated nighttime temperatures compared to the surrounding rural areas. So This creates the Urban Heat Island effect.

Causes of UHI Development:

1. Human Activities: Urbanization creates structures like buildings, roads, & pavements that absorb & retain heat.
2. Urban Canyon Effect: Tall buildings reflect & absorb more sunlight which increases heating in the area.
3. Land Surface Modification: Urban development removes vegetation . It is reducing the cooling effect from plants & increasing heat absorption.
4. Anthropogenic Heat: Activities like transportation, industrial processes, & energy consumption release additional heat into the environment.
5. Albedo Effect: Urban surfaces like concrete & asphalt have lower reflectivity (albedo) & absorb more heat from the sun.
6. Limited Green Spaces: The reduction of parks & vegetation leads to less shade & cooling, increasing heat retention.

Factors Influencing UHI Intensity:

1. Urban Morphology: The layout & density of buildings as well as their height affect how much heat is trapped.
2. Climate: Local climatic conditions, wind patterns & humidity can influence the severity of UHI.
3. Urban Design: The orientation of streets, choice of building materials, & the presence of green infrastructure can either reduce or intensify UHI effects.

Impacts of UHI:

• Health Risks: Higher temperatures increase the risk of heat related illnesses worsen air pollution, & impact public health.
  • • Also Heat waves linked to UHIs lead to more heat-related fatalities.
    • Prolonged heat exposure also affects mental health & academic performance.
• Energy Consumption: Higher temperatures in urban areas increase the need for cooling systems. It is also raising energy consumption & leading to more greenhouse gas emissions.
• Ecological Effects:
  • • UHI affects aquatic ecosystems, raising water temperatures & causing fish kills.
    • It disrupts breeding patterns & habitat ranges for many species.
• Social Impacts: Vulnerable groups elderly & low income communities are disproportionately impacted increasing social inequalities.
  • • According to a study by the International Labour Organization (ILO) heat stress caused the loss of working hours in sectors like agriculture, construction, industry, & services.
    • By 2030 these losses are expected to increase significantly.
      

Mitigation Strategies for UHI:

1. Increasing vegetation cover with parks, green roofs, & tree planting can provide shade & promote evaporative cooling. So it can  reducing UHI effects.
2. Designing pedestrian-friendly environments, incorporating green spaces, & promoting sustainable construction. It  can help to lower UHI intensity.
3. Using reflective roofing materials & heat-absorbing coatings on pavements. It can help to reduce the amount of heat absorbed by urban surfaces.
4. Heat Island Reduction Programs Implementing policies that promote urban forestry, energy-efficient designs, & green building codes. It  can help to mitigate the UHI effect.

 Source: TOI