Chapter – 4

Climate

In this post we have given the detailed notes of Class 11 Geography Book 2 Chapter 4 (Climate) in English. These notes are useful for the students who are going to appear in Class 11 board exams.

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Chapter 4: Climate

Introduction

• Weather: The momentary state of the atmosphere. It describes the atmospheric conditions at a specific time and place, including temperature, pressure, wind direction and velocity, humidity, and precipitation.  
• Climate: The average of weather conditions over a longer period of time. It represents the long-term pattern of weather in a region.  
• Climate change: Changes in the climate that are imperceptible and may be noted after 50 years or even more. These changes can be due to natural causes or human activities.  

Monsoon

• Monsoon: The climate associated with seasonal reversal in the direction of winds.  
• India’s climate: India has a hot monsoonal climate, which is the prevalent climate in south and southeast Asia.  

Factors Determining the Climate of India

• Latitude: The Tropic of Cancer passes through the central part of India, dividing it into tropical and subtropical zones. The tropical zone experiences high temperatures throughout the year, while the subtropical zone experiences extreme climate with high daily and annual range of temperature.  
• The Himalayan Mountains: Act as a climatic divide, shielding the subcontinent from cold northern winds and trapping monsoon winds.  
• Distribution of Land and Water: The differential heating of land and sea creates different air pressure zones, causing a reversal in the direction of monsoon winds.  
• Distance from the Sea: Coastal areas have an equable climate due to the moderating influence of the sea, while interior areas experience extremes of climate.  
• Altitude: Temperature decreases with height, making places in the mountains cooler than places on the plains.  
• Relief: The physiography or relief of India also affects the temperature, air pressure, direction and speed of wind, and the amount and distribution of rainfall.  

Inter Tropical Convergence Zone (ITCZ)

• ITCZ: A low-pressure zone located at the equator where trade winds converge.  
• Position of ITCZ: In July, the ITCZ is located around 20°N-25°N latitudes (over the Gangetic plain), encouraging the development of thermal low over north and northwest India. In winter, the ITCZ moves southward.  
• Influence on Monsoon: The shift of ITCZ causes the trade winds of the southern hemisphere to cross the equator and become southwest monsoon. The southward movement of ITCZ in winter causes the reversal of winds from northeast to south and southwest, called northeast monsoons.  

The Nature of Indian Monsoon

• Complexity: The monsoon is a complex phenomenon that is not fully understood.  
• Onset of the Monsoon: The differential heating of land and sea during the summer months is the mechanism that sets the stage for the monsoon winds to drift towards the subcontinent.  
• Break in the Monsoon: Dry spells during the rainy season due to various reasons, such as the rain-bearing storms not being very frequent along the monsoon trough or the ITCZ, or winds blowing parallel to the coast.  

The Rhythm of Seasons

• Four Seasons: The Indian Meteorological Department recognizes four seasons:
  • The cold weather season (Winter): December and January are the coldest months in the northern plain.  
  • The hot weather season (Summer): April, May, and June are the months of summer in north India.  
  • The southwest monsoon season (Monsoon): The rain in the southwest monsoon season begins rather abruptly, bringing down the temperature substantially.  
  • The retreating monsoon season (Post-monsoon): The months of October and November are known for retreating monsoons.  

El Nino

• El Nino: A complex weather system that appears once every three to seven years, bringing drought, floods, and other weather extremes to different parts of the world.  
• Impact on Indian Monsoon: El Nino is used in India for forecasting long-range monsoon rainfall.  

Distribution of Rainfall

• Average Rainfall: The average annual rainfall in India is about 125 cm, but it has great spatial variations.  
• Areas of High Rainfall: The west coast, Western Ghats, sub-Himalayan areas in the northeast, and the hills of Meghalaya receive rainfall exceeding 200 cm.  
• Areas of Medium Rainfall: Southern parts of Gujarat, east Tamil Nadu, northeastern Peninsula, northern Ganga plain, and the Cachar Valley receive rainfall between 100-200 cm.  
• Areas of Low Rainfall: Western Uttar Pradesh, Delhi, Haryana, Punjab, Jammu and Kashmir, eastern Rajasthan, Gujarat, and Deccan Plateau receive rainfall between 50-100 cm.  
• Areas of Inadequate Rainfall: Parts of the Peninsula, Ladakh, and most of western Rajasthan receive rainfall below 50 cm.  

Monsoons and the Economic Life in India

• Importance of Monsoon: Monsoon is the axis around which the entire agricultural cycle of India revolves, as about 64 percent of people in India depend on agriculture for their livelihood.  
• Regional Variations and Agriculture: Regional variations in monsoon climate help in growing various types of crops.  
• Variability of Rainfall: The variability of rainfall brings droughts or floods every year in some parts of the country, affecting agriculture and the economy.  

Global Warming

• Global warming: The temperature of the world is significantly increasing due to human activities.  
• Greenhouse Gases: Carbon dioxide and other greenhouse gases are contributing to global warming.  
• Impact of Global Warming: Global warming will cause a rise in sea level, an increase in the incidence of annual flooding, and promote insect-borne diseases.

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