Maarg Manthan · Topic 15.3

Urbanization and Climate Change: Urban Heat Island, Pollution in Metros

Environment & Ecology › Climate Change Basics and Causes · Topic 15.3

Cities cause and suffer climate change. They cover a small share of the land but account for most energy use and a large share of greenhouse gas emissions, often put at around 70 percent of energy-related CO2, from buildings, transport, industry and waste. The urban heat island (UHI) is the warming of a city relative to its surroundings, by about 1 to 5 degrees Celsius or more at night, caused by dark roofs and pavements that absorb heat, loss of vegetation and water bodies, tall buildings that trap heat and block wind, and waste heat from vehicles, air conditioners and industry. Pollution in metros arises from vehicles, construction dust, power and industry, waste burning and domestic fuel, producing smog and fine particles. Heat plus pollution raises health risks. India's urban population has grown from about 31 percent in 2011 to well over a third now, with metros such as Delhi, Mumbai, Kolkata and Bengaluru. Responses include cool and green roofs, urban forests, water bodies, public transport, clean fuels, energy-efficient buildings and Heat Action Plans such as Ahmedabad's from 2013.

5 min read · UPSC Prelims · Environment & Ecology · Climate Change Basics and Causes

At a Glance

UHI warming About 1 to 5 C
Main causes Concrete, less green, waste heat
Metro problems Smog, particles, heat
First plan Ahmedabad HAP 2013
Fix Green and cool cities
Exam link UPSC Prelims, Environment & Ecology: Climate Change Basics and Causes

Where Does It Fit?

This topic follows the broad causes of climate change and focuses on cities, then leads to agriculture, which is the other big land-based sector. Previous topic: albedo Human Fossil fuels, land use Pinatubo Cooling after 1991 CO2 280…">Factors and Causes of Climate Change: Extra-Terrestrial, Terrestrial and Anthropogenic Sources. Next topic: Impact of Agriculture on Climate: Carbon Dioxide Emissions, Monoculture, Chemical Fertilizers, Livestock, Pesticides, GM Crops.

What Causes the Urban Heat Island Effect?

Cause	How it heats the city
Dark surfaces	Asphalt and roofs absorb sunlight and release heat at night
Less vegetation and water	Fewer trees and wetlands reduce shade and cooling by evaporation
Urban geometry	Tall buildings trap heat and slow wind, forming street canyons
Waste heat	Vehicles, air conditioners, industry and power plants add heat
Air pollution	Aerosols and haze can hold heat and affect rainfall
Concrete and cement	Hold heat and heat up at night
Climate change	Background warming and heat waves magnify the island effect

What Are the Effects and Remedies?

Heat stress: more heat illness and deaths, especially in poor, crowded areas
Energy demand: air conditioning raises power use and emissions
Air quality: heat speeds the formation of ozone and smog
Water: higher demand and stress
Cool roofs: white or reflective roofs reduce indoor heat
Green roofs and trees: shade and evaporation cool cities
Water bodies: lakes and ponds cool the air
Heat Action Plans: early warning, shelters, water points and schedules for outdoor workers

What Else Should You Remember?

Urban emissions share: cities use most of the world’s energy and cause about 70 percent of energy-related CO2, per UN estimates
Buildings: heating, cooling and lighting are major sources
Transport: private cars and trucks raise emissions and pollution
Urban sprawl: spread-out cities raise travel distances and energy use
Compact city: denser, mixed-use cities cut travel and energy
India’s urbanisation: urban population was about 31 percent in 2011 and is higher now
Metro air pollution: Delhi, Kolkata and other cities often rank high in PM2.5
Vehicle numbers: Delhi and Bengaluru have millions of vehicles
Construction dust: a big source of PM10
Waste burning: adds smoke and toxic gases
Urban flooding: paved surfaces and blocked drains cause floods in Mumbai, Chennai and Bengaluru
Wet bulb temperature: a measure of heat and humidity that matters for human survival
Ahmedabad Heat Action Plan: launched 2013 after the 2010 heat wave; the first in South Asia
Heat waves in India: are officially declared by IMD under set criteria
NDMA guidelines: guide states on heat action plans
Smart Cities Mission: launched 2015 with some green and climate aims
AMRUT 2.0: water and green space focus
Urban forests: Nagar Van scheme
Green building codes: Energy Conservation Building Code and rating systems
Cool Roof Policy: Telangana and other states have introduced cool roof policies
Metro rail: electric mass transit lowers emissions per passenger
Electric buses: reduce pollution in cities
Link to previous: see Factors and Causes of Climate Change: Extra-Terrestrial, Terrestrial and Anthropogenic Sources
Link to next: see Impact of Agriculture on Climate: Carbon Dioxide Emissions, Monoculture, Chemical Fertilizers, Livestock, Pesticides, GM Crops
Link to air quality: see National Air Quality Index and Comprehensive Environmental Pollution Index
Caution: UHI intensity depends on city, season and time of day, so quote it as a range
Exam hint: connect causes to remedies one-to-one
Metro air pollution: vehicles, dust, industry and waste burning raise PM2.5 and NO2 in Delhi, Kolkata and Mumbai, and heat worsens ozone
Heat and health: night-time heat prevents recovery and raises deaths among the elderly and poor
Rainfall changes: urban heat and aerosols may change local rainfall and storm patterns
Water bodies: encroached lakes and wetlands remove natural cooling and flood storage

Why Does It Matter for the Exam?

UHI range: 1 to 5 C
First HAP: Ahmedabad 2013
Remedy: Cool roofs, green cover
Current affairs link: Heat waves
Common errors: confusing UHI with global warming

As an analytical point, cities worsen heat waves and pollution together, so the poor in crowded areas suffer first. Green cover, reflective surfaces, public transport and early warning systems give quick gains.

Why Is This Topic Important?

Cause Concrete, no green
Effect Heat, smog
Fix Green, cool

What Came Next?

The next topic covers the impact of agriculture on climate. Next topic: Impact of Agriculture on Climate: Carbon Dioxide Emissions, Monoculture, Chemical Fertilizers, Livestock, Pesticides, GM Crops.

Key People and Terms

UHI Urban heat island
HAP Heat Action Plan
Cool roof Reflective roof
Street canyon Narrow street with tall buildings
Sprawl Spread-out growth
Wet bulb Heat-humidity measure

Exam Corner

Points to Remember

UHI warms by 1 to 5 C.
Cities cause about 70 percent of energy CO2.
First HAP: Ahmedabad 2013.
Fix: green and cool surfaces.
Delhi, Mumbai are metros.

Do Not Confuse With

UHI and global warming Local city heat versus planetary warming
Cool roof and green roof Reflective versus planted
Heat wave and UHI Weather event versus built-up effect

Memory Hook

Concrete holds the heat, trees give the shade; plan for heat before the heat wave.

Mains Angle

Questions ask for UHI causes and remedies. These points help.

Cause Built-up
Effect Heat, smog
Way Green, HAP

A Question You May Face

An original practice question, not a past paper question.

“Explain the urban heat island effect and discuss the links between urbanisation, pollution and climate change in Indian metros.”

How to Answer

UHI Causes.
Pollution Metros.
Effects Health.
Way Green, HAP.

GS Relevance

Prelims: UHI causes, solutions. GS Paper 1 and 3: urbanisation and climate.

Frequently Asked Questions

What is the urban heat island effect?

The urban heat island effect is the warming of a city compared with its surrounding rural areas, typically by 1 to 5 degrees Celsius and more at night. It is caused by heat-absorbing concrete and asphalt, loss of trees and water bodies, tall buildings that trap heat, and waste heat from vehicles and air conditioners.

How do cities contribute to climate change?

Cities use most of the world's energy and cause a large share of greenhouse gas emissions, often estimated at around 70 percent of energy-related CO2, from buildings, transport, industry and waste. Rapid urbanisation, sprawl and heavy private vehicle use increase emissions, while built-up areas also reduce natural carbon sinks.

What is a Heat Action Plan?

A Heat Action Plan is a set of measures to prepare for and respond to heat waves, including early warning systems, public awareness, adjusting work hours, drinking water points, cool shelters, hospital readiness and long-term steps like cool roofs and tree planting. Ahmedabad launched India's first plan in 2013, after a deadly heat wave in 2010.

How does urban pollution relate to climate change?

Burning of fossil fuels in vehicles, power plants and industry produces both greenhouse gases and air pollutants. Heat promotes ozone formation, while particles such as black carbon warm the air. Climate change also worsens pollution episodes by affecting wind, inversion and heat, so cleaning the air and cutting emissions go together.

How can cities cut heat and emissions?

Cities can reduce heat by planting trees, protecting water bodies, using cool and green roofs and reflective pavements. They can lower emissions through public transport, walkable compact design, energy-efficient buildings, clean cooking and power, better waste management, and electric vehicles, backed by climate-sensitive urban planning.

PYQ Practice — Statement Analysis

1 Urban areas are warmer than their surroundings.

True

The heat island effect.

2 Ahmedabad introduced India's first Heat Action Plan in 1990.

False

In 2013.

3 Cool roofs reflect sunlight.