Class 9 (Geography) Chapter 4 (Climate)

 

Class 9 (Geography)

Chapter 4 (Climate)

 

Notes

 

Factors Affecting India’s Climate:

1. Latitude:
• The Tropic of Cancer divides India into tropical (north) and subtropical (south) regions.
• The northern parts, being closer to the Tropic of Cancer, experience colder climates, while the southern parts, farther away, tend to have warmer climates.
2. Altitude:
• India's diverse topography includes the towering Himalayan range in the north and low-lying coastal areas in the south.
• The Himalayas, with their average height of about 6,000 meters, significantly influence the climate by blocking the penetration of cold air from Central Asia. This barrier effect leads to colder climates in regions adjacent to the Himalayas.
• Conversely, the coastal areas, with altitudes as low as 30 meters, experience milder climates due to their proximity to the sea and lower elevation.
3. Wind and Pressure:
• India's climate is greatly influenced by wind and pressure systems, particularly the seasonal monsoons.
• Northeasterly winds originating from subtropical high-pressure belts of the northern hemisphere play a crucial role in determining weather patterns in India.
• The Coriolis effect, caused by the Earth's rotation, deflects these winds, leading to their circulation towards low-pressure belts and impacting regional climates.

Indian Monsoons: Arrival and Retreat:

• Monsoon Period:
• The Indian monsoon season typically spans from June to mid-September, lasting around 100 to 150 days.
• During this period, India experiences significant and sustained rainfall, commonly referred to as the "burst of monsoon."
• Arrival:
• The onset of monsoon begins with the arrival of monsoon winds at the southern tip of the Indian peninsula in early June.
• These winds then divide into two branches, namely the Arabian Sea branch and the Bay of Bengal branch.
• Geographic features such as mountains influence the direction of monsoon winds, causing them to deflect and bring rainfall to various regions.
• Monsoon:
• The low-pressure system over the Gangetic plains attracts trade winds from the southern hemisphere, contributing to the onset of monsoon rains.
• Regions like the windward side of the Western Ghats receive substantial rainfall, while rainshadow areas experience relatively lower precipitation due to geographical factors.
• Notably, the northeastern parts of India receive significant rainfall during the monsoon season.
• Retreating Monsoon:
• As the sun moves southward in October, the monsoon trough weakens, leading to the onset of the retreating monsoon.
• This transition period is characterized by the withdrawal of monsoon winds from northern regions, resulting in clear skies and a gradual rise in temperature.
• However, the retreating monsoon can also bring about cyclonic disturbances, particularly in the Bay of Bengal, leading to adverse weather conditions in eastern coastal regions.

Monsoons as a Unifying Bond:

• The Indian monsoon holds immense significance as a unifying factor for the country, as it impacts various aspects of life, especially agriculture, which is a vital sector of India's economy.

Definition of Weather and Climate:

• Weather: Refers to the short-term atmospheric conditions of a specific location, encompassing factors such as temperature, humidity, wind speed, and precipitation.
• Climate: Represents the long-term average weather pattern of a region over several decades, providing a more stable understanding of typical weather conditions.

Factors Controlling Climate:

• Latitude: Determines the angle at which sunlight reaches different regions, influencing temperature variations.
• Altitude: Elevation affects temperature through the lapse rate, with higher altitudes generally experiencing cooler temperatures.
• Distance from Sea: Proximity to oceans moderates climate due to maritime influences, impacting factors like temperature and humidity.
• Relief Features: Geographic features such as mountains, plateaus, and plains influence local climate patterns through their effects on wind patterns and precipitation.
• Humidity: Influenced by proximity to water bodies, with coastal areas typically experiencing higher humidity levels.
• Ocean Currents: Cold or warm ocean currents along coastlines influence local climate conditions, affecting temperature and precipitation patterns.

Indian Monsoon:

• The Indian monsoon is a seasonal wind pattern that brings heavy rainfall to the Indian subcontinent from May to September.
• Its formation is driven by differential heating and cooling rates of land and sea, resulting in the development of high and low-pressure systems that steer monsoon winds towards India.

Seasons of India:

• Summer: Characterized by high temperatures, with the occurrence of local hot winds known as loo in some regions.
• Rainy Season: Monsoon winds bring abundant rainfall, vital for agriculture and replenishing water sources.
• Transition Period: Marks the gradual transition between the monsoon and winter seasons, characterized by mild climate conditions.
• Winter: Some northeastern regions experience snowfall, while other parts of the country have cooler temperatures compared to summer.

 

 

Important Question Answers

 

Question 1: What factors influence the climate of India?

Answer : The climate of India is influenced by six major factors:

1. Latitude
2. Altitude
3. Pressure and wind systems
4. Distance from the sea (continentality)
5. Ocean currents
6. Relief features

Question 2: Which atmospheric currents contribute to precipitation along the Malabar Coast?

Answer : Surface winds are responsible for rainfall along the Malabar Coast.

Question 3: Describe jet streams and their impact on India's climate.

Answer : Jet streams are narrow belts of high altitude westerly winds in the troposphere, typically above 12,000 meters. Their speed varies seasonally. Over India, they blow south of the Himalayas throughout the year except in summer. Western cyclonic disturbances in northern India are brought in by this westerly flow. During summer, the subtropical westerly jet stream moves north of the Himalayas. Additionally, a tropical easterly jet stream blows over peninsular India around 14°N during the summer months.

Question 4: Define monsoons and explain the concept of "breaks" in the monsoon pattern.

Answer : Monsoons refer to the seasonal reversal in wind direction during the year. Monsoon rains exhibit "breaks," characterized by alternating wet and dry spells. These breaks indicate intermittent periods of rainfall, with rainy intervals followed by rainless intervals lasting only a few days at a time.

Question 5: What factors contribute to India having a monsoon type of climate?

Answer : India's monsoon type of climate is characterized by distinct seasonal patterns with significant weather changes from one season to another, particularly noticeable in the interior regions. Coastal areas exhibit less temperature variation but varying rainfall patterns. India experiences four main seasons: the cold-weather season, the hot weather season, the advancing monsoon, and the retreating monsoon, with some regional variations.

Question 6: What causes the decrease in rainfall from east to west in Northern India?

Answer : Rainfall patterns vary significantly across Northern India, with the western coast and northeastern regions receiving over 400 cm of rainfall annually, contrasting with less than 60 cm in western Rajasthan and adjoining parts of Gujarat, Haryana, and Punjab. Rainfall is also low in the interior of the Deccan plateau and east of the Sahyadris, as well as around Leh in Jammu and Kashmir. The rest of the country experiences moderate rainfall, with variability being high in regions of low rainfall, making them prone to droughts.

Question 7: Why is the bulk of rainfall in India concentrated over a few months?

Answer :  The bulk of rainfall in India is concentrated over a few months due to the inflow of the southwest monsoon, which brings a significant change in weather. Early in the season, heavy rainfall exceeding 250 cm is observed on the windward side of the Western Ghats, with some rain reaching the Deccan Plateau and parts of Madhya Pradesh despite being in the rain shadow area. The maximum rainfall occurs in the northeastern part of the country, with Mawsynram in the Khasi Hills receiving the highest average rainfall globally. Rainfall decreases from east to west in the Ganga valley, while Rajasthan and parts of Gujarat receive scanty rainfall.

Question 8: What causes the Tamil Nadu coast to receive winter rainfall?

Answer : The Tamil Nadu coast receives winter rainfall due to cyclonic disturbances originating from the west and northwest, particularly characteristic of the cold weather season over the northern plains. These disturbances, originating over the Mediterranean Sea and western Asia, move into India along the westerly flow, bringing much-needed winter rains to the plains and snowfall in the mountains. Despite the small total amount of winter rainfall, locally known as 'mahawat,' it is essential for cultivating 'rabi' crops. The peninsular region experiences minimal seasonal temperature changes during winters due to the moderating influence of the sea.

Question 9: Why is the delta region of the eastern coast frequently struck by cyclones?

Answer : The delta region of the eastern coast is frequently struck by cyclones due to low-pressure conditions over northwestern India, which transfer to the Bay of Bengal by early November. This shift leads to the formation of cyclonic depressions originating over the Andaman Sea, crossing the eastern coasts of India and causing heavy and widespread rain. These tropical cyclones, often highly destructive, frequently affect densely populated deltas like the Godavari, Krishna, and Kaveri, causing significant damage to life and property. Occasionally, these cyclones also impact the coasts of Orissa, West Bengal, and Bangladesh.

Question 10: Why are parts of Rajasthan, Gujarat, and the windward side of the Western Ghats prone to drought?

Answer :  Parts of Rajasthan, Gujarat, and the windward side of the Western Ghats are prone to drought due to the highly variable nature of monsoons, resulting in erratic annual rainfall. Regions with low rainfall, such as parts of Rajasthan, Gujarat, and the windward side of the Western Ghats, experience high variability in rainfall from year to year. While areas with high rainfall are susceptible to floods, those with low rainfall are prone to drought.

Question 11: Explain the regional differences in climatic conditions across India using relevant examples.

Answer :  Despite a general pattern of climatic unity, India exhibits significant regional variations in climatic conditions, primarily in terms of temperature and precipitation. For instance, during summer, temperatures can soar to 50°C in some parts of the Rajasthan desert, whereas they may hover around 20°C in Pahalgam, Jammu and Kashmir. In winter, nighttime temperatures in Drass, Jammu and Kashmir, can plummet to as low as minus 45°C, while Tiruvananthapuram may maintain a comfortable 20°C temperature.

Question 12: How does the monsoon serve as a cohesive force?

Answer :  While India's climate is subject to significant moderating influences, resulting in notable variations in temperature conditions, the monsoon stands out as a unifying factor across the Indian subcontinent. The seasonal transition of wind systems and the consequent changes in weather conditions create a rhythmic cycle of seasons, thereby exerting a perceptible unifying influence despite regional climatic diversity.

 

Question 13: What factors contribute to the mechanism of monsoons?

Answer : The mechanism of monsoons is governed by several key factors that interact to create the seasonal wind patterns and rainfall characteristic of this climatic phenomenon. Firstly, the differential heating and cooling of land and water surfaces play a pivotal role. During the summer months, landmasses, particularly the Indian subcontinent, experience intense heating, leading to the formation of low-pressure systems. In contrast, the surrounding seas maintain relatively higher pressures due to slower heating rates. This stark contrast in pressure gradients sets the stage for the monsoon circulation.

Additionally, the position of the Inter-Tropical Convergence Zone (ITCZ) is instrumental in monsoon formation. In summer, the ITCZ shifts northwards, typically over the Ganga plain. This zone, which is the equatorial trough located around 5°N of the equator, transforms into the monsoon trough during the monsoon season, influencing the direction and intensity of the monsoonal winds.

The presence of a high-pressure area east of Madagascar, situated approximately around 20°S over the Indian Ocean, also plays a crucial role in modulating the Indian Monsoon. Variations in the intensity and position of this high-pressure system influence the monsoonal circulation patterns and rainfall distribution across the Indian subcontinent.

Furthermore, the Tibetan plateau's unique geography and intense heating during summer contribute significantly to the monsoon mechanism. The plateau experiences strong vertical air currents due to heating, resulting in the formation of a high-pressure system at an altitude of about 9 km above sea level. This high-pressure zone over the Tibetan plateau interacts with surrounding atmospheric circulation patterns, further influencing the monsoonal flow.

Finally, the behavior of the jet streams, particularly the westerly jet stream north of the Himalayas and the tropical easterly jet stream over the Indian peninsula during summer, contributes to shaping the monsoonal circulation patterns. These jet streams play a role in steering and directing the movement of moisture-laden air masses, impacting the timing and distribution of rainfall associated with the monsoon.

In summation, the mechanism of monsoons is a complex interplay of differential heating, pressure gradients, the position of the ITCZ, high-pressure systems, unique geographical features like the Tibetan plateau, and the behavior of jet streams, all working together to drive the seasonal winds and rainfall patterns characteristic of the monsoon climate.Top of Form