class 7 Social Science

Weather and Its Elements

Weather affects our daily lives in many ways, such as deciding what clothes to wear. For example:

• Winter calls for warm clothes.
• Summer calls for cool clothes.

Weather and Seasons

This chapter explains how we measure and monitor weather and why weather predictions are important. Weather predictions help us prepare for events like:

• Heavy rain
• Storms
• Droughts
• Heat waves

Understanding weather also helps people like farmers, pilots, sailors, and governments plan and stay safe.What is Weather?

Weather refers to the condition of the Earth’s atmosphere at a specific time and place. We describe weather using words like hot, cold, rainy, cloudy, humid, snowy, or windy.

• Atmosphere: The atmosphere is a layer of gases or air surrounding the Earth.
• Troposphere: This is the lowest layer of the atmosphere where all weather happens. It is 6–18 km thick, with it being thinner at the poles and thicker in the tropics. All plants, animals, and humans live in this layer. 

Troposphere

• The five main elements of weather are:
  1. Temperature: How hot or cold the air is.
  2. Precipitation: Water falling from the sky, like rain, snow, sleet, or hail.
  3. Atmospheric Pressure: The weight of the air pressing down on the Earth’s surface.
  4. Wind: The movement of air, including its speed and direction.
  5. Humidity: The amount of water vapor (gaseous water) in the air.

• Since people experience weather differently (e.g., cold in Chennai may feel pleasant in Kashmir), we need standard ways to measure these elements.
• People have long observed nature to predict weather, like birds flying low, ants moving eggs, frogs croaking, or pine cones closing before rain.
• In India, traditional methods are still used to predict the monsoon.

Let’s Revise

Q: What is the troposphere and why is it important?  View Answer

Q: What are the five main elements used to describe weather?  View Answer
Weather Instruments

Scientists use special instruments to measure these elements of weather accurately.

a) Temperature:

• Measured using a thermometer, which shows how hot or cold it is.

Clinical Thermometer

• Types include clinical and laboratory thermometers, using Celsius (°C) or Fahrenheit (°F) scales (e.g., 15°C = 59°F).
• Some thermometers measure ambient temperature, while others record maximum and minimum temperatures in a day.
• Digital thermometers are more precise and store more data.
  Useful statistics include:
• Range: Maximum temperature minus minimum temperature in 24 hours.
• Mean daily temperature: (Maximum + Minimum) ÷ 2.

b) Precipitation:

• Measured using a rain gauge, which collects rainwater in a cylinder through a funnel.
  Rain Gauge
• A scale measures the depth of water (e.g., 5 mm of water means 5 mm of rainfall).
• For snow, it is melted before measuring.

c) Atmospheric Pressure:

• The weight of air pressing down, felt as “heavy” weather before storms.
• Atmospheric Pressure is higher near sea coasts and lower in mountains, where air is thinner with less oxygen, causing breathlessness at high altitudes.
• Low pressure can form a depression or low-pressure system, leading to storms or cyclones.
• Measured using a barometer in millibars (mb). Normal pressure at sea level is about 1013 mb; below 1000 mb indicates a depression.
  Barometer
• Important for people like mountaineers or soldiers at high altitudes (e.g., Khardung La in Ladakh at 5600 m has about 650 MB).

Let’s Revise

Q: What instrument is used to measure temperature and how does it work?  View Answer

Q: How is precipitation measured and what does a reading of 5 mm mean?  View Answer

d) Wind:

• Wind is the movement of air from high-pressure to low-pressure areas, with speed and direction.
  Movement of Wind
• Important for pilots, sailors, farmers, and weather forecasting, as it affects rain, soil drying, and seed dispersal.
• Wind vane (or weather vane) shows wind direction with a pointer and tail that turns when wind blows.
• Wind sock is a type of wind vane used at airports or industries.
• Anemometer measures wind speed with rotating cups; faster rotation means stronger wind, measured in km/h.

e) Humidity:

• The amount of water vapor in the air, affected by temperature, wind, pressure, and location.
• High humidity (e.g., in coastal Kochi) slows evaporation, while low humidity (e.g., in dry Jaipur) speeds it up.
• Measured as relative humidity: 0% (no water vapor, impossible naturally) to 100% (air saturated with water vapor).
• Dry weather is 20–40% humidity; humid weather is 60–80%.
• Measured using a hygrometer, important for food processing and museums to keep items dry.
  Hygrometer
• High humidity (e.g., 84% in Kochi) makes clothes dry slower and causes more sweating than lower humidity (e.g., 52% in Delhi).

Try yourself:

What instrument is used to measure atmospheric pressure?

• A.Thermometer
• B.Barometer
• C.Rain gauge
• D.Anemometer

View SolutionWeather Stations

A weather station combines instruments like thermometers, rain gauges, barometers, anemometers, and hygrometers to measure weather at one place. Readings are taken regularly to track and forecast weather.

Weather StationAutomated Weather Station (AWS)

• An Automated Weather Station (AWS) uses sensors to measure temperature, humidity, wind, precipitation, and pressure without human help.
  AWS at a Glacial Lake of Sikkim
• AWS is used in agriculture, aviation, navigation, and environmental monitoring for accurate, timely data.
• In 2023, an AWS was set up at a glacial lake in Sikkim at over 4800 meters to warn about weather changes.

Try yourself:

What does an Automated Weather Station (AWS) measure?

• A.Cloud cover
• B.Only rainfall
• C.Temperature and humidity
• D.Wind only

View SolutionPredicting the Weather

Meteorologists collect data from weather instruments over time to predict weather using scientific methods. Predictions are vital due to climate change, which causes more extreme weather like droughts, floods, and cyclones.

Weather Warning for India on 19 May 2024Accurate predictions help:

• Warn fishermen about stormy seas.
• Evacuate coastal areas before cyclones.
• Allow governments to prepare resources for disasters.

The India Meteorological Department (IMD), set up in 1875, issues weather warnings (e.g., a map from 19 May 2024 showed heat waves and severe weather in some states). IMD’s motto, “From the sun arises rain”, reflects how the sun heats water to form rain clouds.

IMDPoints to Remember

• Weather is described by five main elements: temperature, humidity, precipitation, wind, and atmospheric pressure.
• Special instruments like thermometers, rain gauges, barometers, anemometers, and hygrometers are used to measure these elements accurately.
• Data from these instruments help us monitor and predict the weather.
• Weather elements dominate at different times: rainfall in July, temperature in May or December, and wind during hot loo winds or forest fires.
• Weather stations, including Automated Weather Stations (AWS), provide accurate weather data and forecasts.
• Weather is linked to climate, which will be discussed in the next chapter.

Difficult Words

• Weather: The condition of the atmosphere at a specific time and place.
• Atmosphere: The layer of gases (air) surrounding the Earth.
• Troposphere: The lowest layer of the atmosphere where weather happens.
• Precipitation: Water falling from the sky, like rain, snow, sleet, or hail.
• Atmospheric Pressure: The weight of air pressing down on the Earth’s surface.
• Humidity: The amount of water vapor in the air.
• Thermometer: An instrument that measures temperature.
• Rain Gauge: A tool that measures the amount of rainfall.
• Barometer: An instrument that measures atmospheric pressure.
• Wind Vane: A tool that shows the direction of the wind.
• Anemometer: An instrument that measures wind speed.
• Hygrometer: A tool that measures humidity.
• Weather Station: A setup with multiple instruments to measure weather elements.
• Meteorologists: Scientists who study and predict weather.

India’s unique geography sets it apart from many other countries, giving it a distinct national character, as noted by Sri Aurobindo. 

Jog Falls in Karnataka

• From the towering plateaus and majestic waterfalls like Jog Falls in Karnataka, to its vast and varied landscapes.
• India’s geographical diversity shapes not only its natural beauty but also the way people live across the country.
• In 1984, when Rakesh Sharma, the first Indian astronaut, was asked how India looked from space, he famously replied, “Sāre jahān se achchha” — better than the whole world — capturing the pride and uniqueness of India’s geography.

India’s Geographical Diversity

India is the seventh-largest country in the world and an important part of the Indian Subcontinent, which also includes its neighbors like Pakistan, Bangladesh, Nepal, Bhutan, Sri Lanka, and Myanmar. Together, these countries form a region that is diverse in both culture and geography.

Physical Features of India

India’s distinct geography influences its climate, culture, and way of life. The country is divided into five main regions:

1. The Mountain Zone (The Himalayas)
2. The Plains of the Ganga and Indus
3. The Desert Region (The Thar Desert)
4. The Southern Peninsula
5. The Islands

• These regions create varied climates and lifestyles, with some areas having fertile plains for farming and others being arid deserts or cold mountains. The geographical features like mountains, rivers, deserts, and coasts help shape daily life, farming practices, and even festivals across India.
• India’s natural boundaries—The Himalayas to the north, The Thar Desert and Arabian Sea to the west, The Indian Ocean to the south, and The Bay of Bengal to the east—help define the country’s physical limits and contribute to the diverse ecosystems and cultures within it. This variety deeply affects how people live, farm, travel, and celebrate

The Himalayas

The Himalayas, India’s mighty northern mountain range, act as a natural barrier, not only protecting the country but also influencing the climate and culture. These mountains stretch about 2,500 km across six countries: India, Nepal, Bhutan, China, Pakistan, and Afghanistan.

Himalayas

• The Himalayas are home to some of the world’s tallest peaks, including Mount Everest and Kanchenjunga, making it a region of extreme natural beauty and hardship.
• In summer, the snow melts from the Himalayas, feeding rivers like the Ganga, Indus, and Brahmaputra, which supply water to millions for drinking, farming, and industries. This makes the Himalayas often referred to as the ‘Water Tower of Asia’.

The Himalayan range is divided into three main parts:

Himalayan Range

1. Himadri (Greater Himalayas): This is the highest part, home to the Eight Thousanders, mountains towering over 8,000 meters. Very few people live here due to the extreme conditions.
2. Himachal (Lower Himalayas): Known for hill stations like Shimla, Darjeeling, and Mussoorie, this range has a more moderate climate, rich biodiversity, and human habitation.
3. Shivalik Hills (Outer Himalayas): The outermost range, lower in height and filled with dense forests, it forms the transition to the Gangetic Plains.

Try yourself:What natural feature acts as a barrier to protect India in North?

• A.The Thar Desert
• B.The Arabian Sea
• C.The Bay of Bengal
• D.The Himalayas

View Solution

Don’t Miss Out

• The Great Himalayan National Park in Himachal Pradesh is home to many kinds of plants and animals. 
• It is a World Heritage Site recognized by UNESCO. 
• Both the government and the local village communities work together to protect the park’s plants and animals.

Great Himalayan National Park

How the Himalayas Were Formed: An Interesting Story

• India’s collision with Eurasia around 50 million years ago formed the Himalayas.
  India’s Journey to Eurasia
• India, once part of a landmass called Gondwana, slowly moved north and collided with the Eurasian plate. 
• This caused the land to crumple, much like how a carpet wrinkles when pushed, resulting in the towering peaks of the Himalayas. 
• Even today, India is still pushing into Asia, making the mountains grow taller by about 5 mm every year.
• The word ‘Himalaya’ comes from Sanskrit, meaning “abode of snow.”

The Cold Desert of India

Ladakh is India’s cold desert, where winter temperatures drop below -30°C.

Ladakh- Cold Desert of India

• It gets very little rainfall, with rocky terrain, deep valleys, and lakes like Pangong Tso, a salty lake.
• The landscape, called moonland, looks like the moon due to its rugged, eroded rocks formed when India collided with Eurasia.
• Despite harsh conditions, Ladakh has unique wildlife like snow leopards, ibex, and Tibetan antelopes.
• Yaks are vital for the people, used for milk, meat, wool, dung, and transport.
• The Ladakhi people live simply and celebrate colorful festivals like Losar and Hemis Festival.
• The region has ancient monasteries and a unique culture.

Try yourself:

What does the word ‘Himalaya’ mean in Sanskrit?

• A.Mountain range
• B.Rocky terrain
• C.Abode of snow
• D.Cold desert

View SolutionThe Gangetic Plains

As we move southward from the Himalayas, we come to the Gangetic Plains, a large, flat area that is highly fertile and ideal for agriculture. These plains are nourished by rivers like the Ganga, Indus, and Brahmaputra.

Indo-Gangetic Plain

• The Gangetic Plains, also called the Northern Plains, lie south of the Himalayas and are very fertile.
• They are watered by rivers like the Ganga, Indus, and Brahmaputra, which carry minerals from the Himalayas, making the soil ideal for agriculture.
• A large part of India’s population lives here, growing crops like rice and wheat.

Multi Cropping in Gangetic Plains

• The flat land supports a vast transportation network of roads, railways, and rivers used for travel and trade for thousands of years.
• Rivers are named after goddesses like Ganga, Yamuna, and Kaveri, but Brahmaputra means “son of Brahma” and grows bigger in summer due to melting Himalayan snow.
• The plains are home to wildlife like the grey langur, tiger (protected by Project Tiger), and Indian gharial, a reptile on the verge of extinction.
• The peacock, India’s national bird, is also found here.

Try yourself:

Which rivers nourish the Gangetic Plains?

• A.Ganga, Indus, Brahmaputra
• B.Danube, Mekong, Congo
• C.Amazon, Nile, Yangtze
• D.Mississippi, Thames, Seine

View SolutionThe Great Indian Desert or Thar Desert

The Thar Desert is a vast arid region in western India, covering Rajasthan, Gujarat, Punjab, and Haryana.

Thar Desert Location

• It has golden sand dunes, rugged terrain, and a wide-open sky, with dunes rising up to 150 meters formed by wind.
• Daytime temperatures are very high, and nights are cold, with little water available.
• People have adapted with special food, clothing, and lifestyles, like using camels for transport, seen at events like the Pushkar Mela.
• Jaisalmer, the Golden City, has a UNESCO World Heritage site, the Jaisalmer Fort.
• Water is scarce, so women travel long distances to fetch it, and utensils are cleaned with sand to save water.
• Rainwater harvesting systems like taanka or kunds store water for drinking.

The Aravalli Hills

The Aravalli Hills are among the oldest mountains in the world, about 2.5 billion years old, spanning Delhi, Rajasthan, Haryana, and Gujarat.

Aravalli Hills

• Their highest peak, Mount Abu, is over 1700 meters, but most hills are 300–900 meters high.
• They act as a natural barrier, stopping the Thar Desert from spreading eastward.
• The Aravallis are rich in minerals like marble, granite, zinc, and copper. Ancient mines at Zawar show India mastered zinc extraction over 800 years ago.
• Historic forts like Chittorgarh, Kumbhalgarh, and Ranthambore are located here, built in the hills for protection.

Try yourself:

What is the highest peak in the Aravalli Hills?

• A.Mount Abu
• B.Chittorgarh
• C.Kumbhalgarh
• D.Ranthambore

View SolutionThe Peninsular Plateau

A plateau is a flat, elevated landform with steep slopes. The Peninsular Plateau is a triangular area in central and southern India.

Peninsular Plateau

• It is a peninsula, surrounded by water on three sides: the Arabian Sea, Bay of Bengal, and Indian Ocean.
• It is bordered by the Western Ghats (taller, with waterfalls) and Eastern Ghats (lower, broken hills).
• The Deccan Plateau lies between these ranges, a vast flat highland.
• Rivers like Godavari, Krishna, Kaveri, Narmada, and Tapti flow across it, supporting farming, industries, and hydroelectric power.
• The plateau tilts eastward, so most rivers flow toward the Bay of Bengal, except Narmada and Tapti, which flow to the Arabian Sea.
• It is rich in minerals, forests, and fertile land, vital for India’s economy.
• Dense forests are home to tribal communities like Santhal, Gond, Baiga, Bhil, and Korku, who have unique traditions tied to nature.
• Waterfalls on the plateau, like those at Periyakanal, attract tourists and support hydroelectric power.
• The Western Ghats are a UNESCO World Heritage Site with rich biodiversity, including the lion-tailed macaque and insectivorous plants.

Let’s Revise: How do the rivers of the Peninsular Plateau flow, and why?  View Answer
India’s Amazing Coastlines

India’s coastline is over 7500 km long, with beaches, rocky cliffs, forests, and coral reefs. 

Coasts of India

• Deltas are triangular landforms formed when rivers deposit sediments at their mouths, making the land fertile.

The West Coast of India (Gujarat to Kerala):

• Rivers from the Western Ghats form estuaries, with the Narmada and Tapti being the largest.
• It has ports and cities like Mumbai, India’s financial center, active for thousands of years.

West flowing rivers
The East Coast (Ganga delta to Kanyakumari):

• It has wide plains and deltas from rivers like Mahanadi, Godavari, Krishna, and Kaveri, ideal for farming.
• Chilika Lake and Pulicat Lake (a lagoon) are important water bodies.

East Flowing Rivers

Let’s Revise: How is the West Coast of India different from the East Coast?  View Answer

Indian Islands

India has two major island groups: Lakshadweep in the Arabian Sea and Andaman and Nicobar Islands in the Bay of Bengal.

Islands of India

Lakshadweep:

• An archipelago of 36 coral islands near Kerala, not all inhabited.
• Supports fishing and environmental protection.

Andaman and Nicobar Islands:

• Over 500 volcanic islands, divided into Andaman and Nicobar groups.
• Home to coral reefs, beaches, jungles, and ancient tribes.
• Barren Island has India’s only active volcano, which sometimes erupts.
• Their location is strategically important, with a naval dock nearby.

The Delta in West Bengal and the Sundarbans

The Sundarbans is in the delta of the Ganga, Brahmaputra, and their tributaries, split between India and Bangladesh.

Mangroves

• It is a UNESCO World Heritage Site with a unique mix of river, sea, and land.
• The delta has mangroves and is home to the Royal Bengal Tiger and other species.

The Hills of the Northeast

The Northeast hills, part of the Meghalaya Plateau, include the Garo, Khasi, and Jantia hills.

Hills of North- East

• Known for lush greenery, heavy rainfall, and waterfalls like the Seven Sisters Waterfalls.
• The region has some of the highest rainfall in the world, supporting forests, wildlife, and fertile land.
• Mawlynnong Village in the East Khasi Hills is called the cleanest village in Asia, famous for its living root bridges made by weaving tree roots.
• The Shad Suk Mynsiem festival celebrates nature and is held by the Khasi people.

Let’s Revise 

Q: What makes the Andaman and Nicobar Islands special?  View Answer

Q: Why is the Sundarbans an important region?  View Answer
Points to Remember

• India as a Mini-Continent:
  India is often referred to as a mini-continent due to its diverse geographical features, which include:

1. Himalayas
2. Plains
3. Deserts
4. Plateaus
5. Coasts
6. Islands

• The Himalayas – The Water Tower of Asia:
  The Himalayas are often called the ‘Water Tower of Asia’ because they feed major rivers like the Ganga, Indus, and Brahmaputra, providing water for millions of people in the region.

• The Gangetic Plains – Fertility and Population:
• The Gangetic Plains are incredibly fertile, supporting a large portion of India’s population. The rivers in these plains are crucial for:
  • Agriculture
  • Transport
  • Trade
• Adapted Lifestyles in the Thar Desert:
  In the Thar Desert, people have developed unique adapted lifestyles to survive harsh conditions. One such adaptation is rainwater harvesting to save water, which is a scarce resource in the region.
• The Aravalli Hills – Natural Barrier and Rich Minerals:
  The Aravalli Hills prevent the Thar Desert from expanding further. They are also rich in minerals, including marble, granite, zinc, and copper, which have supported mining activities for centuries.
• Peninsular Plateau – Surrounded by Water:
• The Peninsular Plateau is surrounded by water on three sides:
  • Arabian Sea (west)
  • Bay of Bengal (east)
  • Indian Ocean (south)
    It is bordered by the Western Ghats and Eastern Ghats, and the rivers flowing through this region support farming and hydroelectric power generation.
• India’s Coastline – Fertile Deltas and Important Ports:
  India’s coastline, stretching over 7,500 km, is dotted with fertile deltas and important ports, which are crucial for trade and economic activities.
• Lakshadweep and Andaman and Nicobar Islands – Unique Wildlife and Coral Reefs:
  1. Lakshadweep: A coral island group located near Kerala, known for its marine resources and environmental protection efforts.
  2. Andaman and Nicobar Islands: Famous for their unique wildlife, coral reefs, and volcanic activity, these islands are an important part of India’s biodiversity.
• The Sundarbans – UNESCO World Heritage Site:
  The Sundarbans are a UNESCO World Heritage Site known for their mangroves and the Royal Bengal Tiger. This unique delta region, located in the lower Ganga-Brahmaputra delta, is a biodiversity hotspot.
• The Northeast Hills – Heavy Rainfall and Living Root Bridges:
  The Northeast hills of India, part of the Meghalaya Plateau, experience some of the highest rainfall in the world.
  This region is also known for its living root bridges, a unique feature created by weaving tree roots over time.

Difficult Words

• Subcontinent: A large part of a continent, like India and its neighbors.
• Landforms: Natural features of the Earth, like mountains, plains, and plateaus.
• Biodiversity: The variety of plants and animals in an area.
• Tributaries: Smaller rivers that flow into a larger river.
• Glacier: A large mass of ice that moves slowly.
• Plateau: A flat, elevated landform with steep slopes.
• Peninsula: Land surrounded by water on three sides.
• Estuaries: Areas where rivers meet the sea, mixing fresh and saltwater.
• Deltas: Triangular landforms formed by river sediments at the mouth.
• Archipelago: A group of islands.
• Mangroves: Trees that grow in coastal areas with roots in water.