Geography Class 10 Notes Chapter 4 Climate Maharashtra Board

Introduction

• Climate refers to the average weather conditions of a place over a long period, including temperature, rainfall, and winds.
• This chapter compares the climate of India and Brazil, focusing on temperature, rainfall, winds, and their effects.
• Key skills: Reading maps, graphs, and understanding how geographical features influence climate.

Climate of Brazil

Overview

• Brazil has a wide range of climates due to its vast latitudinal extent (from 5°15’N to 33°45’S).
• Tropical climate dominates near the equator (hot and humid), while a temperate climate is found near the Tropic of Capricorn in the south.
• Most of Brazil lies in the tropical zone, with the equator passing through the northern part.

Temperature

Average Range: 21°C to 28°C (based on isotherms in Figure 4.1).

Northern Brazil (e.g., Amazon valley): Hotter, with temperatures of 25°C-28°C, little seasonal variation due to proximity to the equator.

Southern Brazil: Cooler, with lower average temperatures due to higher latitude.

Coastal Areas: Mild and humid due to the influence of the Atlantic Ocean.

Highest Temperatures: Found in the northern regions near the equator.

Lowest Temperatures: Found in the southern regions near the Tropic of Capricorn.

Rainfall

Main Sources: Rainfall comes from Southeast Trade Winds and Northeast Trade Winds blowing from the Atlantic Ocean.

Types of Rainfall:

• Orographic Rainfall: Occurs when winds hit the Great Escarpment and Brazilian Highlands, causing heavy rain in coastal areas (e.g., 2000 mm in the Amazon valley).

Highest Rainfall: Amazon valley (around 2000 mm annually).

Moderate Rainfall: Northeastern coast (1000-1200 mm).

Rain-Shadow Area: The Drought Quadrilateral in the northeastern Brazilian Highlands receives minimal rainfall (600-800 mm) because the escarpment blocks moisture-laden winds.

Rainy Season: Varies by region, but generally occurs from December to April (based on Figure 4.4).

Winds

Direction: Winds blow from the southeast and northeast (trade winds).

Reason: High-pressure systems in the Atlantic Ocean push these winds towards Brazil.

Obstruction: The Great Escarpment and Brazilian Highlands block the winds, causing orographic rainfall on the windward side and dry conditions on the leeward side.

Equatorial Winds: Between 0° to 5°N/S, winds move vertically (convection), creating a weak convergence zone, which reduces cyclone formation.

Special Features

Tropical Cyclones: Rarely occur in Brazil because:

• The trade wind convergence zone near the equator is weak.
• Winds move vertically, not horizontally, preventing cyclone formation.
• Stable temperatures near the equator reduce cyclone triggers.

Snowfall: Rare, but southern Brazil occasionally experiences snowfall (e.g., in 1879, 1957, 1985) when polar air masses reach the region.

Drought Quadrilateral: A dry region in the northeast with hot temperatures, sparse vegetation, and frequent droughts due to the rain-shadow effect.

City Climate (Based on Figure 4.4)

• Manaus: Hot, humid, little temperature variation, high rainfall.
• Belem: Hot, high rainfall, especially from January to May.
• Rio de Janeiro: Warm, humid, moderate rainfall, equable climate.
• Porto Alegre: Cooler, maximum temperature range, distinct seasons.

Climate of India

Overview

• India has a monsoon-type climate, characterized by seasonal winds and heavy rainfall.
• The Tropic of Cancer passes through the middle, making most of India tropical with high temperatures.
• Climate varies due to latitude, altitude, and geographical features like the Himalayas and Indian Ocean.

Temperature

• Average: High throughout the year due to the Tropic of Cancer.
• Maximum Temperatures: Thar Desert, Rajasthan (up to 50°C in Ganganagar in June).
• Minimum Temperatures: Jammu and Kashmir, Himalayas (down to -48°C in Kargil in winter).
• Direction of Increase: Temperature increases from north to south.
• Coastal Areas: Milder due to the Indian Ocean’s moderating effect.

Rainfall

Main Source: Southwest Monsoon Winds (June-September) bring most of India’s rainfall.

Highest Rainfall:

• Western Ghats and Eastern Himalayas (>4000 mm).
• Mawsynram and Cherrapunji in Meghalaya (11,872 mm and 11,777 mm, wettest places in the world).

Lowest Rainfall: Jaisalmer, Western Rajasthan (<120 mm, driest part of India).

Retreating Monsoon: Northeast Monsoon winds (October-December) bring rainfall to Tamil Nadu and parts of the Peninsula.

Types of Rainfall:

• Orographic Rainfall: Caused by the Western and Eastern Ghats and Himalayas blocking monsoon winds.
• Convectional Rainfall: Less prominent in India, occurs in hot, humid conditions.

Rain-Shadow Area: Parts of Gujarat and Rajasthan (e.g., Thar Desert) receive low rainfall because the Aravali ranges block monsoon winds.

Winds

Southwest Monsoon Winds:

• Blow from the Indian Ocean (high pressure) to India’s low-pressure areas (Punjab Plains, Thar Desert) in summer.
• Bring heavy rainfall, especially in coastal areas and the Himalayas.

Northeast Monsoon Winds:

• Retreating monsoon winds blow from the northeast towards the Indian Ocean, bringing rainfall to Tamil Nadu.

Himalayan Influence: Blocks cold northern winds and forces monsoon winds to rise, causing orographic rainfall.

Seasons (Indian Meteorological Department)

1. Hot Weather Season: March-May, high temperatures, low pressure develops.
2. Monsoon Season: June-September, heavy rainfall from Southwest Monsoon.
3. Retreating Monsoon Season: October-December, rainfall in Tamil Nadu from Northeast Monsoon.
4. Cold Weather Season: January-February, cooler temperatures, especially in the north.

Special Features

• Natural Disasters: India faces erratic rainfall, droughts, floods, and cyclones frequently due to its tropical location.
• Tropical Cyclones: Common in India, especially in the Bay of Bengal, affecting eastern coastal states.
• Semi-Arid Conditions: Found in Western Andhra Pradesh due to low rainfall in the rain-shadow of the Western Ghats.
• Three-Crop Regions: Parts of India (e.g., West Bengal, Tamil Nadu) grow three crops a year due to high rainfall and fertile soil.

City Climate (Based on Figure 4.5)

• Delhi: Extreme climate, hot summers, cold winters, moderate rainfall (July-August).
• Kolkata: Hot, humid, high rainfall during monsoon, similar temperature curve to Delhi.
• Mumbai: Equable climate, mild temperatures, heavy monsoon rainfall.
• Chennai: Equable climate, high rainfall during Retreating Monsoon (October-December).

Comparison of Brazil and India’s Climate

Similarities

• Both are tropical countries with hot climates in most regions.
• Both experience orographic rainfall due to highlands (Brazilian Highlands, Himalayas/Western Ghats).
• Coastal areas in both have mild, humid climates.
• Both face natural disasters like floods and droughts.

Differences

Climate Type:

• India: Monsoon-type climate with distinct wet and dry seasons.
• Brazil: Tropical climate with less seasonal variation in the north, temperate in the south.

Rainfall:

• India: Heavy monsoon rainfall (June-September), retreating monsoon in Tamil Nadu.
• Brazil: Rainfall from trade winds, no monsoon, rainy season varies by region.

Winds:

• India: Southwest and Northeast Monsoon winds.
• Brazil: Southeast and Northeast Trade winds.

Cyclones:

• India: Frequent tropical cyclones in the Bay of Bengal.
• Brazil: Rare tropical cyclones due to weak trade wind convergence.

Snowfall:

• India: Common in the Himalayas.
• Brazil: Rare, only in southern regions during exceptional conditions.

Rain-Shadow Areas:

• India: Thar Desert (blocked by Aravalis).
• Brazil: Drought Quadrilateral (blocked by Great Escarpment).