Chapter 4: Climate| Class 11 Geography Notes

Class 11 Geography Chapter 4: Climate Notes: The climate is an important topic in CBSE Class 11 Geography. Chapter 4 Geography covers climate, which means the weather conditions in an area over a long time. It explains how different things like where you are on Earth, how high up you are, and even how close you are to the sea affect the weather. The chapter also talks about the monsoon winds in India, which bring important rain for farming. It tells us about how rainfall varies across India and how climate change is affecting our country.

These notes are helpful for students studying Class 11 Geography as they provide a comprehensive understanding of the concept of climate. regions. All the important topics have been compiled in CBSE Notes Class 11 Geography Chapter 4: Climate.

Chapter 4: Climate| Class 11 Geography Notes

Climate

Climate covers the long-term patterns of weather across a large area, usually spanning more than thirty years.

Weather refers to the current atmospheric conditions in a particular place at a specific time.

• Both climate and weather are shaped by factors like temperature, air pressure, wind, humidity, and rainfall, which collectively determine the atmospheric state.
• The year is divided into seasons based on the monthly changes in atmospheric conditions. These seasons include Winter, Summer, and Rainy Seasons, each characterized by distinct weather patterns throughout the year.

Unity and Diversity In the Monsoon Climate

The monsoon climate underscores India’s connection with the broader Southeast Asian region. However, this perspective of a unified monsoon climate shouldn’t overshadow the significant regional variations that shape the weather and climate across different parts of India.

For example, the climates of Kerala and Tamil Nadu in the south starkly differ from those of Uttar Pradesh and Bihar in the north, despite all falling under the monsoon climate category. India’s climate exhibits numerous regional diversities manifested in wind patterns, temperature fluctuations, rainfall distribution, seasonal rhythms, and wetness or dryness levels. These regional disparities can be seen as sub-types of the monsoon climate.

Taking a closer look at these regional variations in temperature, winds, and rainfall, it’s evident that India experiences extreme diversity. For instance, while temperatures in western Rajasthan can soar to 55°C in summer, they can plummet to minus 45°C around Leh during winter. Similarly, Churu in Rajasthan may scorch at over 50°C in June, whereas Tawang in Arunachal Pradesh might only reach 19°C on the same day. Likewise, Drass in Ladakh can drop to minus 45°C on a December night, while Thiruvananthapuram or Chennai might hover around 20°C or 22°C. These examples illustrate the significant seasonal and regional temperature variations across India.

Moreover, regional differences in precipitation are notable, with snowfall occurring in the Himalayas while rainfall predominates elsewhere. The amount of precipitation also varies widely, with Cherrapunji and Mawsynram in Meghalaya receiving over 1,080 cm of rainfall annually, contrasting sharply with Jaisalmer in Rajasthan, which barely sees 9 cm. Similarly, Tura in Meghalaya might receive as much rainfall in a single day as Jaisalmer receives in ten years. The northwest Himalayas and western deserts receive less than 10 cm of rainfall annually, while Meghalaya experiences over 400 cm.

The frequency and intensity of rain-bearing storms differ across regions. For instance, the Ganga delta and Odisha’s coastal plains experience frequent heavy storms in July and August, while the Coromandel coast often remains dry during these months. Although rainfall is predominant across most of the country from June to September, Tamil Nadu’s coastal areas receive rain at the beginning of the winter season. Despite these disparities, India’s climate maintains a monsoonal rhythm and character.

Factors Determining The Climate of India

India’s climate is influenced by several key factors:

Latitude: India’s vast expanse covers different latitudinal zones. The northern part, lying beyond the Tropic of Cancer, experiences a sub-tropical and temperate climate, while the southern part falls within the tropical zone. The tropical zone, closer to the equator, has consistently high temperatures throughout the year, with minimal daily and annual temperature variations. In contrast, the northern regions experience extreme climates with significant daily and annual temperature fluctuations.

Himalayan Mountains: The Himalayas and their extensions as a crucial climatic barrier. These towering mountains shield the subcontinent from the cold northern winds originating near the Arctic circle. They play a important role in intercepting monsoon winds, causing them to release moisture within the Indian subcontinent.

Distribution of Land and Water: India’s geographical positioning, with the Indian Ocean surrounding it on three sides in the south and a continuous mountain barrier in the north, affects its climate. Water heats up and cools down slower than land, leading to differential heating and creating distinct air pressure zones around the subcontinent. These pressure differences contribute to the reversal in the direction of monsoon winds.

Distance from the Sea: Coastal areas experience a more moderate climate due to the influence of the sea, while inland regions are subject to more extreme weather patterns. Coastal regions like Mumbai and the Konkan coast have relatively stable temperatures and weather conditions compared to inland areas like Delhi, Kanpur, and Amritsar, which witness significant seasonal variations.

Altitude: Temperature decreases with altitude, with mountainous regions being cooler than plains. For instance, Agra and Darjeeling are situated at similar latitudes, but Darjeeling, at a higher altitude, experiences much lower temperatures than Agra, especially in January.

Relief: The geographical features, or relief, of India also impact its climate. Regions like the windward side of the Western Ghats and Assam receive heavy rainfall during the monsoon season, whereas the leeward side of the southern plateau remains comparatively dry due to its sheltered position along the Western Ghats.

The Nature of Indian Monsoon

The climate of India is significantly shaped by monsoon winds, characterized by the seasonal reversal of the wind system known as the “monsoon.” Here are some key facts to better understand the mechanism of the monsoons:

• Differential heating and cooling of land and water create low pressure over the Indian landmass while the surrounding seas experience relatively high pressure.
• The shift in the position of the Inter-Tropical Convergence Zone (ITCZ) over the Ganga plain during summer, known as the monsoon trough, plays a crucial role in the monsoon season.
• The presence of a high-pressure area east of Madagascar, approximately 20°S over the Indian Ocean, influences the Indian Monsoon.
• Intense heating of the Tibetan plateau during summer leads to strong vertical air currents and the formation of low pressure over the plateau, approximately 9 km above sea level.
• Movement of the westerly jet stream north of the Himalayas and the presence of the tropical easterly jet stream over the Indian peninsula during summer also impact the Indian Monsoon.
• Changes in pressure conditions over the southern oceans, as well as irregularly periodic variations in winds and sea surface temperatures over the tropical eastern Pacific Ocean known as Southern Oscillation (SO), also affect the monsoons.

Onset of the Monsoon

Historically, it was believed that differential heating of land and sea during summer triggers the monsoon winds’ movement towards the subcontinent. By April and May, when the sun is directly overhead at the Tropic of Cancer, the vast northern landmass of the Indian Ocean heats up intensely. This creates a deep low-pressure area in the northwestern part of the subcontinent.

Meanwhile, the southern Indian Ocean, with its slower heating, maintains high pressure. As a result, the low-pressure system attracts the southeast trades across the Equator, leading to a northward shift in the position of the Intertropical Convergence Zone (ITCZ). The southwest monsoon can be viewed as a continuation of the southeast trades, diverted towards the Indian subcontinent after crossing the Equator. These winds cross the Equator between longitudes 40°E and 60°E.

The monsoon, a complex climatic phenomenon, has puzzled scientists for centuries. Recent global studies have provided some understanding of its key aspects, such as its onset and breaks.

It was thought that the differential heating of land and sea during summer triggers the monsoon winds towards the subcontinent. As the northern Indian Ocean heats up intensely in April and May, it creates a deep low-pressure area in the northwestern part of the subcontinent. Meanwhile, the slower-heating southern Indian Ocean maintains high pressure.

This pressure difference draws the southeast trades across the Equator, leading to a northward shift in the position of the Intertropical Convergence Zone (ITCZ). The southwest monsoon is essentially a continuation of the southeast trades, diverted towards the Indian subcontinent after crossing the Equator. These winds typically cross the Equator between longitudes 40°E and 60°E.

The shift in the position of the Intertropical Convergence Zone (ITCZ) is also linked to the withdrawal of the westerly jet stream from its usual position over the northern Indian plain, south of the Himalayas. The easterly jet stream only establishes itself along the 15°N latitude after the withdrawal of the western jet stream. This easterly jet stream is considered responsible for the onset of the monsoon in India.

Entry of Monsoon into India : The southwest monsoon arrives over the Kerala coast by June 1st and then progresses swiftly to reach Mumbai and Kolkata between June 10th and 13th. By mid-July, the southwest monsoon covers the entire subcontinent.

Break in the Monsoon

During the southwest monsoon period, if there’s a lack of rain for one or more weeks after a few days of rainfall, it’s termed as a “break” in the monsoon. These dry spells are common during the rainy season and occur for various reasons:

(i) In northern India, rainfall may fail if the rain-bearing storms are infrequent along the monsoon trough or the Intertropical Convergence Zone (ITCZ) over this region.

(ii) Over the west coast, dry spells are associated with days when winds blow parallel to the coast.

The Seasons

India experiences four main seasons:

1. The cold weather season (Winter)
2. The hot weather season (Summer)
3. The advancing monsoon (Rainy Season)
4. The retreating monsoon with some regional variations (Transition Season)

The Cold Weather Season (Winter):

• Winter starts around mid-November and lasts till February.
• December and January are the coldest months in northern India.
• Temperature decreases from south to north.
• Days are warm, while nights are cold with clear skies, low humidity, and variable winds.
• This season is crucial for cultivating “rabi” crops.

The Hot Weather Season (Summer):

• From March to May, India experiences rising temperatures and falling air pressure, especially in the north.
• Strong, hot, dry winds known as “loo” blow during the day in north and northwest India.
• Pre-monsoon showers occur towards the end of summer, aiding in the early ripening of mangoes.

Advancing Monsoon (The Rainy Season):

• The southwest monsoon originates from southeast trade winds over warm subtropical areas, crossing the equator and entering India as the southwest monsoon.
• The monsoon covers the country for about a month, with regions like Mawsynram in the Khasi Hills receiving the highest average rainfall globally.
• The monsoon is characterized by breaks in rainfall, influenced by the movement of the monsoon trough and the frequency and intensity of tropical depressions.

Retreating/Post Monsoons (The Transition Season):

• October-November marks the transition from the hot rainy season to dry winter conditions.
• The retreat of the monsoon brings clear skies and rising temperatures.
• Day temperatures are high, while nights are cool and pleasant.
• Towards the end of October, temperatures start to decrease rapidly in northern India.

Distribution of Rainfall

• The western coast and northeastern India receive an annual rainfall of over about 400 cm.
• Western Rajasthan and adjoining parts of Gujarat, Haryana, and Punjab experience less than 60 cm of rainfall annually.
• Rainfall is low in the interior of the Deccan plateau and east of the Sahyadris.
• Snowfall occurs mainly in the Himalayan region.
• The annual rainfall varies significantly from year to year.

Global Warming

Change is a fundamental law of nature, and climate has undergone transformations in the past, both globally and locally. While changes are ongoing, they may not always be easily noticeable. Geological evidence suggests that at one point, a significant portion of the Earth was covered in ice. You may have heard about the ongoing debate on global warming, which is primarily attributed to human activities such as large-scale industrialization and the presence of polluting gases in the atmosphere.

Carbon dioxide emissions from burning fossil fuels are a major concern, contributing to the gradual increase in atmospheric temperatures. Other gases like methane, chlorofluorocarbons, and nitrous oxide, collectively known as greenhouse gases, also play a role in enhancing the greenhouse effect. These gases trap heat in the atmosphere, leading to global warming. The consequences of global warming include the melting of polar ice caps and mountain glaciers, resulting in a rise in sea levels.

Over the past 150 years, the mean annual surface temperature of the Earth has increased, and it is projected to rise further by about 2°C by the year 2100. This temperature increase will lead to various changes, including a rise in sea levels, which could result in increased flooding. Climatic changes may also impact the spread of diseases such as malaria and alter agricultural patterns, affecting human populations and ecosystems.

For Indian sea coasts, a rise in sea levels by 50 cm above the present level could have significant implications, potentially leading to coastal flooding and other environmental changes.

Class 11 Geography Chapter 4: Climate- FAQs

What is climate?

Climate refers to the long-term patterns of temperature, humidity, wind, and other atmospheric conditions in a specific region over an extended period, spanning more than thirty years.

How does climate differ from weather?

While weather describes the short-term atmospheric conditions in a specific location at a particular time, climate encompasses the overall weather patterns and variations observed across a wide area over a long period.

What are the factors that influence climate?

Various factors influence climate, including latitude, altitude, pressure and wind systems, distance from the sea, ocean currents, and relief features such as mountains and valleys.

What is the significance of monsoon winds in the climate of India?

Monsoon winds play a crucial role in the climate of India, bringing seasonal rainfall essential for agriculture. The seasonal reversal of wind patterns during monsoon season leads to distinct wet and dry periods, shaping the country’s climate.

How does the distribution of rainfall vary across India?

Rainfall distribution in India varies significantly, with parts of the western coast and northeastern regions receiving over 400 cm of rainfall annually, while arid regions like western Rajasthan receive less than 60 cm. Rainfall patterns are influenced by monsoon winds, relief features, and proximity to the sea.