Weather is what we experience every hour or day — it might be raining, or there could be bright sunshine, a lot of wind, etc. The weather keeps changing. Climate, on the other hand, is the pattern of weather an area or a region experiences over a long period of time — several decades at least. This pattern varies from region to region.

Seasons occur as the Earth revolves around the Sun. Each season lasts for a few months and recurs every year. Seasons are related to both weather and climate — the weather changes with the season, and the pattern of seasons is connected to the long-term climate.

The Six Traditional Indian Seasons (Ṛitus)

Human, plant and animal life are in rhythm with the ṛitus or seasons. The crops we grow, the food we eat, the clothes we wear change with the season. Trees bloom with vasanta/spring, shed leaves in śharad/autumn, and animals develop thick fur in winter months.

India is a land of diversity — equally true of its climate. The major climate types found in India are:

Fig. 3.5 — Famous Indian Hill Stations: Darjeeling, Udhagamandalam (Ooty), Munnar, Shimla

The climate of any region is determined collectively by all factors below. Describing the climate involves describing the patterns of temperature, precipitation (rain or snowfall, fog or mist) and wind conditions over three decades or more.

a) Latitude

Places near the Equator (low latitudes) are warmer; those near the poles (high latitudes) are colder. This is because:

• At the Equator, sun's rays are nearly perpendicular — energy is concentrated on a smaller area.
• In polar regions, rays are inclined/oblique — energy is distributed over a larger surface.
• At higher latitudes, rays must pass through more of the Earth's atmosphere, further dissipating their energy.

Fig. 3.4 — At the equator exposure to the sun's rays is concentrated, but near the poles it is dispersed over a wide area

Indian example: Kanniyakumari and the Nicobar Islands (close to Equator) are warm/hot almost throughout the year, while Srinagar (in the north, higher latitude) is much cooler.

b) Altitude

Temperature decreases as altitude increases because:

• Atmospheric pressure and air density decrease with altitude — as air gets less dense, it gets cooler.
• The Sun heats the Earth's surface — the farther from the surface, the less hot the air.
• The Himalayas are so high that many peaks maintain temperature below water's freezing point, keeping them covered in snow.

c) Proximity to the Sea

Coastal areas have temperatures that do not vary much — summers are not too hot and winters not too cold — because the sea acts as a temperature moderator. As you move inland, temperatures become more extreme.

Fig. 3.6 — Distance from the Sea: Coastal regions have moderate temperatures; inland regions show extreme temperature ranges

The mechanism: Land heats and cools faster than the sea. In summer, land heats up more than sea → cool sea air moderates coastal temperatures. In winter, land loses heat faster than sea → warm sea air prevents extreme cold in coastal areas.

d) Winds

Wind can move masses of warmer or cooler air, affecting both temperature and humidity (and thus precipitation).

Fig. 3.7 — Wind and cyclonic circulation patterns over India

e) Topography

Topography = the totality of the physical surface features of an area (mountains, hills, valleys, slopes, coasts, etc.).

Microclimate

A microclimate is a climate localised in a small area, which differs from the climate of the surrounding region. It has a unique pattern of temperature, humidity, precipitation, etc.

• Enclosed valleys and some forests have microclimates of their own.
• Urban Heat Islands: Cities with large numbers of buildings/concrete structures and very little vegetation trap heat — they are often much warmer than surrounding regions.
• Microclimates influence local flora and fauna, crops grown, and impact human health.

Fig. 3.8 — Aravallis and Urban Heat Islands: contrast between green natural areas and heat-trapping concrete cities

The monsoon season is central to life in India. During the monsoon months, rivers fill up, soil is soaked with water, crops grow and life thrives.

Mechanism of Monsoons

The mechanism of monsoons is complex but based on the simple fact that land heats up or cools down faster than the ocean. Monsoons bring out the fundamental relationship between temperature, pressure and wind movement.

Fig. 3.9 — Southwest monsoon (summer) and Northeast monsoon (winter) — wind directions over India

Southwest Monsoon in India

Monsoon rains typically advance from the southern tip of India in early June, moving northward over several weeks until they cover the entire subcontinent by mid-July. It is not a smooth progression.

The Western Ghats act as a natural barrier:

• Western slopes of the Western Ghats → receive much rainfall
• Deccan Plateau to the east → receives less rainfall, often with interruptions (rain shadow area)

This is called the summer or southwest monsoon — 'southwest' reflecting the direction the winds come from.

Northeast Monsoon

As winter approaches, winds reverse and blow from the land to the ocean. These are dry winds bringing cold weather to south India. However, a part of them passes over the Bay of Bengal, collecting moisture, and brings rainfall to parts of east and south India. This is the winter or northeast monsoon.

Fig. 3.10 — Mawsynram, Meghalaya — World's highest average annual rainfall (~11,000 mm)

Traditional Knowledge for Predicting Monsoon

Fig. 3.13 — Cyclone Fani: showing low pressure centre, cloud formation, and winds bringing moist air from sea

Our lives are deeply connected with and dependent on the climate. The impact of climate is visible in local cultures — India has many festivals associated with seasons and agricultural activities.

Festivals Linked to Climate and Agriculture

Fig. 3.11 — Seasonal Festivals of India: Bihu, Chhath Puja, Makar Sakranti, Baisakhi, Pongal, Awe Winter Festival, Hemis, Losoong, Gudi Padwa, Lohri, Onam

Economic Impact of Climate

'Monsoon failure' refers to poor rainfall during the monsoon season. Its cascading effects:

• Agriculture suffers
• People (often women) must walk long distances in search of water
• Agricultural labourers migrate to cities
• Food (grains, vegetables, fruits) becomes costlier, fuelling inflation
• Industrial activity (dependent on water and predictable weather) is disrupted

India's diverse weather patterns can bring about extreme conditions such as cyclones, floods, landslides and forest fires. These events affect people's lives, disrupt agriculture, damage infrastructure and disturb local economies.

a) Cyclones

Every year, the Indian coastline, especially the eastern coast, witnesses several cyclones. Past cyclones have caused loss of human and animal life, damaged property and infrastructure, uprooted trees and caused soil erosion.

The India Meteorological Department (IMD) tracks cyclones and provides information on their formation, evolution, and place of landing.

Formation of Cyclones:

• Atmospheric pressure near the sea becomes lower than surrounding areas → creates a low-pressure system
• Air from surrounding areas (including from the sea) moves into the low-pressure area, bringing moisture and rain
• When the low-pressure system is intense and wind speeds are high → cyclone forms
• Winds collect moisture, form clouds, and rotate inwards towards the centre of the depression
• This cloudless centre is called the 'eye of the cyclone'

Fig. 3.14 — Eye of the Storm: the cloudless, calm centre of a cyclone surrounded by swirling clouds

b) Floods

A flood occurs when water overflows into normally dry land — due to heavy rainfall generating huge run-off that the land cannot absorb, or due to excessive accumulation in rivers/lakes until banks are breached.

c) Landslides

A landslide is the sudden collapse of rock, soil, or debris, often triggered by heavy rain, earthquakes or volcanic activity.

Vulnerable regions: Himachal Pradesh, Uttarakhand, Sikkim, Arunachal Pradesh, Western Ghats, and other hilly regions. These events often occur during the monsoon.

Human causes increasing landslide risk:

• Cutting down of forests (deforestation)
• Building infrastructure without following approved methods
• Constructing too many buildings that block natural water flow

d) Forest Fires

Forest fires are uncontrolled fires spreading rapidly across vegetation, fuelled by dry climatic conditions, droughts or high winds. Human carelessness is another frequent cause.

Vulnerable states: Uttarakhand, Himachal Pradesh, Madhya Pradesh, Chhattisgarh, and the Western Ghats.

Consequences: Destruction of large forest areas, harm to wildlife, degradation of the ecosystem, spoiling of air quality, displacement of local communities — both environmental and economic consequences.

Fig. 3.15 — Four major climate-related disasters in India: Cyclone, Landslide, Forest Fire, Flood

Climate change refers to significant, long-term changes in the climate — on the scale of the planet or on a regional scale — involving shifts in temperature, precipitation and weather events.

Greenhouse Effect and Global Warming

In Earth's natural carbon cycle, CO₂ and other gases are released gradually into the atmosphere and trap heat from the Sun. This natural greenhouse effect warms Earth enough to support life.

However, human activities — industry, transportation, agriculture — have released enormous amounts of greenhouse gases in just a few centuries. This sudden increase traps extra heat, causing rapid global warming and disrupting climate patterns that plants, animals, and human societies have adapted to over thousands of years.

Impact on India

Early in 2025, India's average temperature was 1 to 3°C above normal, resulting in a much shorter and milder winter than usual. This affected agricultural production and many small-scale industries.

Climate Change Mitigation Measures

Governments worldwide, including India's, promote:

• Cutting down on greenhouse gas emissions
• Planting trees (afforestation/reforestation)
• Boosting renewable energy and improving energy efficiency
• Promoting sustainable lifestyles

These often clash with the desire for economic growth and increased consumption — a key policy tension.

NCERT Exercise Answers — Matching (Q.1)