Class 9 Social Science (NCERT)
Chapter 4
Climate
1. Choose the correct answer from the four alternatives given below.
(i) Which one of the following places receives the highest rainfall in the world?
(a) Silchar (c) Cherrapunji
(b) Mawsynram (d) Guwahati
Ans: (b) Mawsynram
(ii) The wind blowing in the northern plains in summers is known
(a) Kaal Baisakhi (c) Trade Winds
(b) Loo (d) None of the above
Ans: (b) Loo
(iii) Which one of the following causes rainfall during winters in north-western part of India.
(a) Cyclonic depression (c) Western disturbances
(b) Retreating monsoon (d) Southwest monsoon
Ans: (c) Western disturbances.
(iv) Monsoon arrives in India approximately in:
(a) Early May (c) Early June
(b) Early July (d) Early August
Ans: (c) Early June.
(v) Which one of the following characterises the cold weather season in India?
(a) Warm days and warm nights
(b) Warm days and cold nights
(c) Cool days and cold nights
(d) Cold days and warm nights
Ans: (b) Warm days and cold nights.
2. Answer the following questions briefly.
(i) What are the controls affecting the climate of India?
Ans: The climate of India is influenced by a variety of factors, including:
Latitude: India is located in the tropical zone, between the Tropic of Cancer and the Equator. This means that the country receives a lot of sunlight throughout the year, which contributes to its warm temperatures.
Altitude: The Himalayas, the world's tallest mountain range, form a barrier to cold winds from Central Asia. This helps to keep India's temperatures from dropping too low in the winter.
Ocean currents: The Indian Ocean currents, particularly the Indian Ocean Monsoon Current, bring warm water to India's shores. This warm water helps to moderate the country's climate and contributes to its rainfall.
Wind systems: The Southwest Monsoon winds, which blow from the Indian Ocean to India from June to September, bring most of the country's rainfall. The Northeast Monsoon winds, which blow from India to the Bay of Bengal from December to February, bring some rainfall to the eastern coast of India.
Relief features: The Himalayas and the Thar Desert also influence India's climate. The Himalayas block cold winds from Central Asia, while the Thar Desert contributes to the country's hot, dry summers.
These factors combine to create a diverse range of climates in India. The country has everything from hot, dry deserts to cool, mountainous regions.
(ii) Why does India have a monsoon type of climate?
Ans: India has a monsoon type of climate due to the differential heating of land and water bodies, which creates a seasonal reversal of wind patterns.
Differential heating refers to the phenomenon where land heats up more quickly than water when exposed to sunlight. This is because water has a higher heat capacity than land, meaning that it requires more energy to raise its temperature.
As a result of differential heating, the landmass of India becomes much hotter than the surrounding ocean during the summer months. This creates a low-pressure area over the land, while a high-pressure area persists over the ocean.
To equalize this pressure difference, winds begin to blow from the ocean towards the land. These winds, known as the Southwest Monsoon, carry moisture from the ocean and bring heavy rainfall to India from June to September.
During the winter months, the land cools down more quickly than the ocean. This creates a high-pressure area over the land and a low-pressure area over the ocean. Winds then blow from the land towards the ocean, carrying little moisture and bringing little rainfall to India.
This seasonal reversal of wind patterns is responsible for India's monsoon type of climate, characterized by a wet summer and a dry winter.
(iii) Which part of India does experience the highest diurnal range of temperature and why?
Ans: The part of India that experiences the highest diurnal range of temperature is the Thar Desert, located in the western part of the country, particularly in the state of Rajasthan. The diurnal range of temperature in this region can reach up to 50°C (90°F), with daytime temperatures soaring to 50°C (122°F) and nighttime temperatures dropping to near 0°C (32°F).
Several factors contribute to the extreme diurnal range of temperature in the Thar Desert:
1. Geographical Location: The Thar Desert is situated far from the moderating influence of the ocean, making it more susceptible to extreme temperature fluctuations.
2. Low Humidity: The desert's low humidity levels allow for rapid heat gain during the day and rapid heat loss at night.
3. Sandy Soil: The sandy soil of the desert has a low heat capacity, meaning it can quickly absorb heat during the day and release it rapidly at night.
4. Clear Skies: The clear skies in the Thar Desert allow for more sunlight to reach the surface during the day, further intensifying the heating effect.
5. Absence of Vegetation: The lack of vegetation in the desert reduces the amount of shade and evapotranspiration, which would otherwise help to moderate temperatures.
Due to these factors, the Thar Desert experiences some of the most extreme diurnal temperature ranges in the world. The drastic temperature swings can have significant impacts on the region's ecology and human inhabitants.
(iv) Which winds account for rainfall along the Malabar coast?
Ans: The winds that account for rainfall along the Malabar coast are the Southwest Monsoon winds. These winds originate from the Indian Ocean and blow towards the Indian subcontinent from June to September. As they approach the Western Ghats mountain range, they are forced to rise, which cools them and causes them to release their moisture. This moisture falls as rain along the Malabar coast, which is the western coastal strip of India.
The Southwest Monsoon is responsible for about 80% of the annual rainfall in India. It is an essential part of the country's climate and economy, as it provides water for agriculture, drinking, and hydropower.
Here are some of the key characteristics of the Southwest Monsoon:
*It is a seasonal wind that blows from June to September.
*It originates from the Indian Ocean and blows towards the Indian subcontinent.
*It brings heavy rainfall to the Malabar coast and other parts of India.
*It is an essential part of India's climate and economy.
(v) What are Jet streams and how do they affect the climate of India?
Ans: Jet streams are narrow bands of strong winds that flow high in the atmosphere, typically at altitudes of 9,000 to 12,000 meters (30,000 to 40,000 feet). They are characterized by their high speeds, which can reach up to 400 kilometers per hour (250 miles per hour). Jet streams are also relatively narrow, with a width of only a few hundred kilometers (a few hundred miles).
Jet streams play an important role in global weather patterns, and they can have a significant impact on the climate of India. Here are some of the ways in which jet streams affect India's climate:
.They influence the movement of weather systems. Jet streams can steer storms and cyclones, bringing them to or away from India. For example, the westerly jet stream is responsible for bringing western disturbances to India in the winter months. These disturbances bring rain and snow to northern India.
.They affect the distribution of rainfall. Jet streams can help to focus rainfall in certain areas, and they can also divert rainfall away from other areas. For example, the easterly jet stream is responsible for bringing rainfall to the southern peninsula of India during the summer months.
Jet streams can also have a more subtle impact on India's climate by influencing the overall circulation of the atmosphere. For example, the westerly jet stream can help to keep the air over India warm in the winter months, while the easterly jet stream can help to keep the air over India cool in the summer months.
Overall, jet streams are an important factor in India's climate, and they play a role in a variety of weather phenomena. Understanding how jet streams work is important for weather forecasting and climate modeling.
(vi) Define monsoons. What do you understand by "break" in monsoon?
Ans: Monsoons are seasonal winds that bring heavy rainfall to certain regions of the world, especially in Asia. The word "monsoon" comes from the Arabic word "mausim," meaning "season." Monsoons are caused by the differential heating of land and sea. During the summer, the land heats up faster than the sea, creating a low-pressure area over the land. Winds rush in from the sea to fill this low-pressure area, bringing with them moisture-laden air. This moisture-laden air rises and cools, forming clouds and rain.
A "break" in the monsoon is a period of reduced rainfall or a dry spell during the monsoon season. This can happen when the monsoon trough, an area of low pressure, shifts away from the region. Breaks in the monsoon can last for a few days to a few weeks and can have a significant impact on agriculture and water resources.
(vii) Why is the monsoon considered a unifying bond?
Ans: Monsoons are considered a unifying bond for several reasons:
1. Agricultural dependence: The monsoon rains are crucial for agriculture in many parts of the world, particularly in India and Southeast Asia. Farmers rely on the monsoon to irrigate their crops and ensure a good harvest. The arrival of the monsoon is eagerly awaited by farmers across the region, and its timing and intensity can have a significant impact on their livelihoods.
2. Cultural influence: Monsoons play a deep cultural role in many societies, with festivals and traditions tied to the arrival of the rains. These celebrations serve as communal gatherings, reinforcing social bonds and cultural identity. For instance, the Onam festival in Kerala, India, marks the arrival of the monsoon and is a time of feasting, cultural performances, and boat races.
3. Ecological impact: The monsoon rains are vital for the ecological balance of the regions they affect. They replenish water sources, sustain forests, and support diverse ecosystems. The monsoon's influence on the environment connects people to their natural surroundings and fosters a sense of shared stewardship.
4. Economic significance: The monsoon plays a significant role in the economies of many countries, particularly in agriculture-based economies. The timing and intensity of the rains can affect crop yields, food prices, and overall economic activity. The monsoon's influence on economic fortunes binds people together and highlights their shared dependence on the natural world.
5. Shared experience: The monsoon experience is a unifying factor for people across diverse social, ethnic, and linguistic groups. The common anticipation of the rains, the shared joy of the first showers, and the collective anxiety during dry spells create a sense of shared experience and common destiny.
In summary, monsoons serve as a unifying bond by connecting people through their dependence on agriculture, cultural practices, ecological well-being, economic fortunes, and shared experiences. The monsoon's rhythmic cycle and its influence on various aspects of life create a sense of interconnectedness and shared identity among people within the monsoon-affected regions.
3. Why does the rainfall decrease from the east to the west in Northern India.
Ans: The rainfall in Northern India decreases from east to west due to the following factors:
1. Moisture depletion: As the moisture-laden winds from the Bay of Bengal travel westward across the Indo-Gangetic Plains, they gradually lose moisture due to precipitation and evaporation. By the time they reach western India, they carry significantly less moisture, resulting in reduced rainfall.
2. Orographic uplift: The Aravalli Hills in western India act as a barrier to the monsoon winds, forcing them to ascend. As the winds rise, they cool and condense, releasing their remaining moisture as rainfall on the windward side of the hills. This further reduces the moisture content of the winds as they descend on the leeward side, leading to even less rainfall in the westernmost parts of Northern India.
3. Distance from moisture source: The regions in eastern India are closer to the Bay of Bengal, the primary source of moisture for the monsoon, compared to the regions in western India. This proximity allows eastern India to receive more direct and intense rainfall from the monsoon.
4. Continental heating: The landmasses in western India tend to heat up more during the summer, creating a warm, rising air column. This rising air column can deflect the monsoon winds upwards, preventing them from effectively delivering rainfall to the western regions.
In conclusion, the combination of moisture depletion, orographic uplift, distance from the moisture source, and continental heating contributes to the observed decrease in rainfall from east to west in Northern India.
4. Give reasons as to why.
(i) Seasonal reversal of wind direction takes place over the Indian subcontinent?
Ans: Yes, the seasonal reversal of wind direction occurs over the Indian subcontinent. This is due to the seasonal changes in pressure patterns over the region.
Summer Monsoon
During summer, the landmass of Asia heats up more than the surrounding oceans. This creates a low-pressure area over the land, while the oceans remain at a higher pressure. As a result, winds blow from the cooler oceans towards the warmer land, bringing with them moisture from the oceans. These moisture-laden winds are known as the southwest monsoon. They bring heavy rainfall to most parts of India, from June to September.
Winter Monsoon
In winter, the situation reverses. The landmass of Asia cools down more than the surrounding oceans, creating a high-pressure area over the land. The oceans remain at a lower pressure, and winds blow from the cooler land towards the warmer oceans. These dry, continental winds are known as the northeast monsoon. They bring little rainfall to most parts of India, from October to May.
The Impact of Seasonal Reversal
The seasonal reversal of wind direction has a significant impact on the climate and agriculture of India. The summer monsoon brings essential rainfall for agriculture, while the winter monsoon brings cooler temperatures and drier conditions. The reversal also affects the distribution of wildlife, with many animals migrating between different parts of the country according to the season.
Additional Factors
In addition to the seasonal changes in pressure patterns, other factors can also affect the wind direction over the Indian subcontinent. These include the El Niño-Southern Oscillation (ENSO) and the Madden-Julian Oscillation (MJO). ENSO is a climate pattern that affects the Pacific Ocean, and it can have a significant impact on the strength and timing of the monsoon. The MJO is a shorter-term climate pattern that can also affect the monsoon.
Overall, the seasonal reversal of wind direction is a key feature of the climate of the Indian subcontinent. It has a major impact on the region's weather, agriculture, and wildlife.
(ii) The bulk of rainfall in India is concentrated over a few months.
Ans: Yes, the bulk of rainfall in India is concentrated over a few months due to the southwest monsoon, which typically lasts from June to September. This seasonal wind system brings moisture-laden air from the Indian Ocean to the subcontinent, causing heavy rainfall in most parts of the country.
The southwest monsoon is driven by the pressure difference between the land and the ocean. During the summer, the land heats up more than the ocean, creating a low-pressure area over the land. This low pressure attracts the moisture-laden winds from the ocean, which rise as they reach the land and cool, forming clouds and rain.
The southwest monsoon is responsible for about 80% of India's annual rainfall. The timing and intensity of the monsoon can vary from year to year, which can have a significant impact on agriculture and water resources.
Here is a breakdown of the average rainfall in India by month:
June: 100 millimeters (3.9 inches)
July: 250 millimeters (9.8 inches)
August: 300 millimeters (11.8 inches)
September: 200 millimeters (7.9 inches)
As you can see, the majority of rainfall in India occurs during the monsoon season. This concentration of rainfall is important for agriculture, as it allows farmers to grow crops without having to rely on irrigation.
The southwest monsoon is also important for the ecology of India. The rains help to replenish water resources, support forests, and sustain diverse ecosystems.
Overall, the southwest monsoon is a vital part of the Indian climate. It is responsible for most of the country's rainfall, and it plays a key role in agriculture, water resources, and ecology.
(iii) The Tamil Nadu coast receives winter rainfall.
Ans: Yes, the Tamil Nadu coast receives winter rainfall, unlike most of India which receives rainfall during the summer monsoon. This is due to the unique geographical location of Tamil Nadu and the seasonal reversal of wind direction over the Indian subcontinent.
Geographical Location
Tamil Nadu is located on the southeastern tip of India, jutting out into the Bay of Bengal. This positioning means that it is directly exposed to the northeast monsoon winds that blow from the Bay of Bengal during the winter months (October to May). These winds bring moisture from the Bay of Bengal, which is released as rainfall when they encounter the Eastern Ghats, a mountain range that runs along the eastern coast of India.
Seasonal Reversal of Wind Direction
Winter rainfall is an important part of the climate of the Tamil Nadu coast, and it plays a vital role in the region's agriculture, water resources, and ecosystems.
(iv) The delta region of the eastern coast is frequently struck by cyclones.
Ans: Yes, the delta region of the eastern coast of India is frequently struck by cyclones. This is due to a combination of geographical and meteorological factors.
Geographical Factors
1. Proximity to Bay of Bengal: The delta region of the eastern coast is located in close proximity to the Bay of Bengal, a large body of warm water that serves as a breeding ground for cyclones. The warm water provides the necessary energy for cyclones to form and intensify.
2. Shallow Coastal Shelf: The coastal shelf along the eastern coast of India is relatively shallow, which means that cyclones can travel closer to the shore before encountering deeper water and weakening. This allows cyclones to make landfall with greater force and cause more damage.
3. Shape of the Coastline: The coastline of the eastern coast of India curves inward, creating a bay-like structure. This curvature can amplify storm surges, which are large waves that can inundate coastal areas and cause significant flooding.
Meteorological Factors
1. Favorable Wind Conditions: The Bay of Bengal experiences strong winds during the pre-monsoon and post-monsoon seasons, which are the peak periods for cyclone formation. These winds provide the necessary lift and rotation for cyclones to develop.
2. El Niño-Southern Oscillation (ENSO): ENSO is a climate pattern that affects the Pacific Ocean and can influence the strength and frequency of cyclones in the Bay of Bengal. During El Niño years, there is a higher likelihood of more intense cyclones forming in the Bay of Bengal.
3. Madden-Julian Oscillation (MJO): The MJO is a shorter-term climate pattern that can also affect the formation of cyclones in the Bay of Bengal. The MJO can trigger periods of increased convection and wind shear, which are favorable conditions for cyclone development.
Impact of Cyclones
Cyclones can cause widespread damage to the delta region of the eastern coast of India, including:
*Storm Surges: Storm surges can inundate coastal areas, causing flooding and widespread damage to infrastructure and property.
* High Winds: Strong winds can topple trees, structures, and power lines, disrupting transportation and communication networks.
* Heavy Rainfall: Cyclones can bring heavy rainfall, leading to flash floods, landslides, and soil erosion.
* Loss of Life: Cyclones can cause loss of life due to drowning, injuries from debris, and infrastructure collapse.
(v) Parts of Rajasthan, Gujarat and the leeward side of the Western Ghats are drought-prone.
Ans: Yes, parts of Rajasthan, Gujarat, and the leeward side of the Western Ghats are drought-prone. This is due to a combination of factors, including:
* Geographical location: These regions are located in the rain shadow of the Aravalli Hills and Western Ghats, respectively. This means that they do not receive much direct rainfall from the monsoon winds.
*Climate patterns: The regions experience hot and dry summers, and cool and dry winters. This lack of rainfall throughout the year makes them susceptible to drought.
*Human activities: Overexploitation of groundwater resources, deforestation, and unsustainable agricultural practices can exacerbate drought conditions.
As a result of these factors, parts of Rajasthan, Gujarat, and the leeward side of the Western Ghats frequently experience water shortages, crop failures, and other negative impacts of drought.
5. Describe the regional variations in the climatic conditions of India with the help of the Suitable examples.
Ans: India's vastness and diverse topography give rise to a wide range of climatic conditions across the country. From the snow-capped peaks of the Himalayas to the sun-drenched Thar Desert, each region experiences its unique weather patterns and seasonal variations.
1. Temperature Variations
Temperature variations are starkly evident across India. In the north, the Himalayan region experiences extreme cold, with temperatures dropping below -40°C in the winter. In contrast, the southern tip of India, particularly Kerala, enjoys a warm and humid climate, with average temperatures rarely falling below 20°C.
Example: Mawsynram in Meghalaya, nestled in the Khasi Hills, holds the record for the highest average annual rainfall in the world, receiving over 11,800 mm of rain.
2. Rainfall Distribution
Rainfall patterns in India are largely influenced by the monsoon system. The southwest monsoon, arriving from June to September, brings abundant rainfall to most parts of the country. However, the distribution of rainfall is uneven, with some regions receiving heavy rainfall while others remain relatively dry.
Example: The Thar Desert in Rajasthan, located in the northwestern part of India, receives less than 12 cm of annual rainfall, making it one of the driest regions in the country.
3. Altitude and Mountain Ranges
Altitude plays a significant role in determining the climate of a region. As elevation increases, temperatures tend to decrease, and rainfall patterns become more erratic. Mountain ranges act as barriers to moisture-laden winds, creating distinct climatic zones on their windward and leeward sides.
Example: The Western Ghats mountain range along the western coast of India intercepts the southwest monsoon, resulting in heavy rainfall on its windward slopes. In contrast, the leeward side of the Western Ghats, including parts of Karnataka and Maharashtra, experiences a drier climate.
4. Coastal Influence
Coastal regions experience the moderating influence of the ocean, which tends to stabilize temperatures and increase humidity. Coastal areas generally have milder summers and warmer winters compared to inland regions.
Example: The coastal city of Mumbai experiences relatively moderate temperatures throughout the year, with average highs ranging from 27°C to 34°C and average lows from 18°C to 25°C.
6. Discuss the mechanism of monsoons.
Ans: Sure, here is a discussion of the mechanism of monsoons:
Monsoons are seasonal winds that bring heavy rainfall to certain regions of the world, particularly in Asia. The Indian monsoon, for example, is responsible for over 75% of India's annual rainfall.
The mechanism of monsoons is driven by differential heating. During the summer, landmasses heat up faster than oceans. This creates a low-pressure area over the land and a high-pressure area over the ocean. Winds blow from high-pressure areas to low-pressure areas, so moisture-laden winds from the ocean are drawn towards the land.
As the moisture-laden winds rise over the land, they cool and condense. This condensation leads to the formation of clouds and rain. The amount of rainfall that falls depends on a number of factors, including the strength of the winds, the topography of the land, and the amount of moisture in the air.
Topography can also play a role in the distribution of monsoon rainfall. Mountains can force the moist winds to rise, leading to heavier rainfall on the windward side of the mountains. For example, the Western Ghats mountains in India receive significantly more rainfall than the leeward side of the mountains.
Monsoons are crucial for agriculture and water resources in many parts of the world. They play a vital role in the economies and ecosystems of monsoon-affected regions. However, monsoons can also be destructive. Heavy rains can lead to flooding and landslides, and droughts can occur if the monsoons fail.
Here is a table summarizing the key points about the mechanism of monsoons:
7. Give an account of weather conditions and characteristics of the cold season.
Ans: Sure, here is an account of weather conditions and characteristics of the cold season:
Temperature
The most obvious characteristic of the cold season is its lower temperatures. In most parts of the world, the average temperature drops significantly during this time of year. In some regions, temperatures can drop below freezing for extended periods. This is due to the reduced angle of sunlight reaching the Earth's surface, which causes less heat to be absorbed.
Precipitation
Precipitation patterns also change during the cold season. In many temperate regions, snowfall becomes common, with some areas receiving significant accumulations. In other regions, rainfall may continue, but it often falls as a cold rain or sleet.
Humidity
Humidity levels generally tend to be lower during the cold season. This is because colder air has a lower capacity to hold moisture. However, there are some exceptions, such as coastal areas where the ocean provides a source of moisture.
Daylight Hours
The cold season is also characterized by shorter daylight hours. This is because the Earth's axis is tilted, and the hemisphere that is experiencing winter receives less direct sunlight. The shorter daylight hours can lead to a feeling of lethargy and a decrease in mood for some people.
Wind
Winds can be more variable during the cold season, with strong gusts and storms more common. This is due to the increased contrast in temperature between land and sea, which creates stronger pressure gradients.
Overall, the cold season is characterized by cooler temperatures, different precipitation patterns, lower humidity, shorter daylight hours, and more variable winds. These conditions can have a significant impact on people, plants, and animals.
Here are some additional details about the cold season in different parts of the world:
*Temperate regions: In temperate regions, the cold season typically lasts from December to February. During this time, temperatures can drop below freezing, and snowfall is common.
*Subtropical regions: In subtropical regions, the cold season is milder, with temperatures rarely dropping below freezing. Snowfall is less common, but it can occur in some areas.
*Tropical regions: In tropical regions, the cold season is not as pronounced. However, there may be a slight decrease in temperatures and humidity during this time.
8. Give the characteristics and effects of the monsoon rainfall in India.
Ans: Sure, here is a summary of the characteristics and effects of the monsoon rainfall in India:
Characteristics of the Monsoon Rainfall in India
*Duration: The monsoon season in India typically lasts from June to September, with the peak rainfall occurring in July and August.
*Intensity: The monsoon brings heavy rainfall to most parts of India, with some regions receiving over 2,000 millimeters (79 inches) of rain per year.
*Distribution: The distribution of monsoon rainfall is uneven, with some regions receiving much more rain than others. This is due to a variety of factors, including topography, distance from the coast, and the influence of mountain ranges.
*Variability: The monsoon rainfall is highly variable from year to year. This variability can have a significant impact on agriculture and water resources.
Effects of the Monsoon Rainfall in India
*Agriculture: The monsoon rainfall is essential for agriculture in India. The majority of India's farmland is rainfed, and the monsoon provides the water needed for crops to grow.
*Water Resources: The monsoon rainfall replenishes India's water resources, including rivers, lakes, and groundwater reservoirs. This water is essential for drinking, irrigation, and industry.
*Ecosystems: The monsoon rainfall supports a wide variety of ecosystems in India, including forests, grasslands, and wetlands.
*Economy: The monsoon rainfall has a significant impact on the Indian economy. Good monsoon rains can lead to increased agricultural production and economic growth. However, poor monsoon rains can lead to droughts and economic hardship.
Overall, the monsoon rainfall is a vital part of the Indian climate. It plays a critical role in agriculture, water resources, ecosystems, and the economy.
Answer Type By : Himashree Bora.
Post ID: DABP002246
