Class 9th Geography Climate Notes

1. Introduction

• Weather: Short-term atmospheric conditions (temperature, rainfall, humidity, wind, etc.) at a particular place and time.
• Climate: The average weather conditions over a long period (generally 30–35 years) for a large area.

India’s climate is monsoonal, influenced by multiple factors like location, relief, winds, and the Himalayas.

• Major seasons in India:
  1. Cold Weather Season (Winter) – December to February
  2. Hot Weather Season (Summer) – March to May
  3. Advancing Monsoon (Rainy Season) – June to September
  4. Retreating Monsoon (Transition Season) – October to November

2. Factors Affecting Climate of India

India’s climate is controlled by a complex set of factors:

2.1 Latitude

• Tropic of Cancer (23½° N) divides India into:
  • Tropical zone (South) → high temperatures, small annual range.
  • Sub-tropical zone (North) → moderate temperatures, larger annual range.

2.2 Altitude

• India has high mountains (Himalayas) and coastal lowlands.
• Himalayan ranges act as barriers:
  • Protect India from cold Siberian winds → prevents severe winters.
  • Block monsoon winds → cause heavy rainfall.

2.3 Pressure and Wind Systems

• Climate depends on:
  • Pressure belts.
  • Surface winds.
  • Seasonal winds.

Important wind systems:

• Southwest Monsoon Winds (June–Sept): Bring most of India’s rainfall.
• Northeast Monsoon Winds (Oct–Nov): Cause winter rainfall in Tamil Nadu.

2.4 Distance from the Sea

• Continentality (land–sea influence):
  • Coastal regions → moderate climate (Mumbai, Chennai).
  • Interior regions → extreme climate (Delhi, Kanpur).

2.5 Ocean Currents

• Warm and cold currents influence coastal climates.
• Example:
  • Warm Gulf Stream and cold Labrador Current (globally).
  • In India, Indian Ocean currents modify monsoon patterns.

2.6 Relief

• Mountains, valleys, and plateaus influence rainfall.
• Example:
  • Western Ghats → heavy rainfall on windward side, dry conditions on leeward side (rain-shadow region).
  • Himalayas block cold winds, force monsoon winds to rise → rainfall.

3. The Indian Monsoon

3.1 Importance

• Monsoon = “seasonal reversal of winds.”
• Lifeline of India → determines agriculture, economy, water supply, and lifestyle.

3.2 Mechanism of Monsoon

1. Differential Heating of land and water → creates low pressure over NW India and high pressure over Indian Ocean.
2. Shift of ITCZ (Inter Tropical Convergence Zone): Moves northwards in summer.
3. Trade Winds: SE trade winds cross equator, get deflected, enter India as SW monsoon winds.
4. Westerly Jet Stream: Affects onset and withdrawal of monsoons.
5. Tibetan Plateau heating: Creates strong low pressure, pulling monsoon winds.

3.3 Onset of Monsoon

• Hits Kerala coast around 1 June.
• Advances to cover most of India by mid-July.

3.4 Breaks in Monsoon

• Monsoon does not bring continuous rainfall.
• Rainfall occurs in spells with dry intervals.

3.5 Retreating Monsoon

• Winds withdraw from NW India in October.
• Causes clear skies, rising temperatures.
• Tamil Nadu coast gets rainfall due to retreating NE monsoons.

4. Seasons in India

4.1 Cold Weather Season (Winter)

• Duration: December–February.
• Features:
  • North India → cold, dry winds.
  • South India → mild, pleasant.
  • Western disturbances (Mediterranean origin) bring winter rain to NW India and snowfall in Himalayas.

4.2 Hot Weather Season (Summer)

• Duration: March–May.
• Features:
  • Rising temperatures.
  • Heat waves (loo) in northern plains.
  • Pre-monsoon showers (Mango showers in Kerala, Kalbaisakhi in Bengal).

4.3 Advancing Monsoon (Rainy Season)

• Duration: June–September.
• Features:
  • SW monsoon winds → heavy rainfall.
  • Rainfall is unevenly distributed:
    • Meghalaya (Mawsynram) = heaviest rainfall in world.
    • Rajasthan, Gujarat = very little rainfall.

4.4 Retreating Monsoon (Transition Season)

• Duration: October–November.
• Features:
  • High temperature + humidity in day.
  • Clear skies, pleasant evenings.
  • Rainfall in Tamil Nadu, Andhra, Kerala (due to NE monsoon).

5. Distribution of Rainfall

• High rainfall areas (>200 cm): NE India, Western Ghats, Andaman & Nicobar.
• Moderate rainfall areas (100–200 cm): Indo-Gangetic plain, Peninsular plateau.
• Low rainfall areas (<100 cm): Rajasthan, Gujarat, Ladakh.
• India shows regional variations:
• Meghalaya: >400 cm annually.
• Jaisalmer: <10 cm annually.

6. Monsoon as a Unifying Bond

Despite variations, monsoon unifies India by:

• Bringing rains almost everywhere.
• Linking agriculture, festivals, economy, and culture.
• Determining cropping seasons (Kharif & Rabi).

7. Climatic Regions of India

According to Köppen’s classification:

1. Tropical Wet (Equatorial) – West coast, NE India.
2. Tropical Dry (Arid/Semi-Arid) – Rajasthan, Gujarat, interior Deccan.
3. Sub-tropical Humid – Ganga-Brahmaputra plains, NE India.
4. Mountain Climate – Himalayas.

8. Global Warming and Climate Change in India

• Rise in average temperatures → melting glaciers, erratic monsoons.
• Increased frequency of floods, droughts, cyclones.
• Need for sustainable climate action.

Quick Revision Points

• Weather vs Climate → Weather = short-term; Climate = long-term.
• Factors → Latitude, altitude, pressure & winds, distance from sea, relief, ocean currents.
• Monsoon → Seasonal reversal of winds; influenced by ITCZ, jet streams, differential heating.
• Seasons → Winter, Summer, Advancing Monsoon, Retreating Monsoon.
• Rainfall Distribution → Uneven, from Mawsynram (>400 cm) to Rajasthan (<10 cm).
• Unity → Monsoon is India’s unifying bond.