Notes on Climate Chapter

Understanding Weather and Climate

Weather is the short-term state of the atmosphere, while climate is the average weather over a long period, typically 30 years or more.

• Elements of Weather: These include temperature, pressure, wind direction, humidity, and precipitation.
• Variability: Weather can change rapidly within hours or days, while climate changes slowly over time.
• Regional Differences: For instance, Rajasthan can experience temperatures soaring to 55°C, while Tawang in Arunachal Pradesh might barely reach 19°C on the same day.

Monsoon Climate

The monsoon season is a significant climatic feature in India characterized by seasonal winds that change direction:

• Two Types of Monsoons in India: The southwest monsoon (dominant in the summer) and the northeast monsoon (occurring in winter).

• Indian Monsoon Unity and Diversity: The monsoon reflects broad climatic unity in southeast Asia, but there are significant regional variations in rainfall, temperature, and other weather conditions.

Regional Variations in Temperature and Rainfall

• Temperature Extremes: Temperature varies widely across regions. For example:

  • In summer, Churu, Rajasthan can record 50°C, while Leh can drop to -45°C in winter.

• Precipitation Extremes: Cherrapunji, Meghalaya, has one of the highest rainfalls globally, surpassing 1080 cm annually, while Jaisalmer, Rajasthan, may receive less than 9 cm.

• Influence of Topography: The Himalayas act as a climatic barrier, shielding the subcontinent from cold northern winds while trapping moisture-laden monsoons.

Factors Determining Climate

1. Latitude: India spans both tropical and temperate zones.
2. Altitude: Higher elevations, such as in the Himalayas, experience lower temperatures significantly affecting regional climates.
3. Relief: The geomorphology of India affects air pressure and rainfall distribution (i.e., windward vs. leeward effects).
4. Distance from the Sea: Coastal areas generally have a milder climate compared to inland regions, known for extreme temperatures.
5. Inter-Tropical Convergence Zone (ITCZ): This is crucial for monsoon development, as shifting ITCZ influences seasonal weather patterns in India.

The Nature of the Indian Monsoon

• Onset and Break in the Monsoon: The southwest monsoon typically begins in Kerala by June 1st and reaches northern India by mid-July. A break is defined as a period when rain fails for weeks despite the anticipated monsoon patterns.
• Global Patterns and E.I Niño: The E.I Niño phenomenon can disrupt Indian monsoons, causing delays or irregularities in rainfall, significant for forecasting.

Seasonal Rhythms in Indian Climate

1. Cold Weather Season: Mid-November to February characterized by low temperatures and dry conditions.
2. Hot Weather Season: March to June with rising temperatures often leading to heat waves.
3. Southwest Monsoon Season: June to September defined by heavy rainfall across the country.
4. Retreating Monsoon Season: October and November feature the monsoon retreating, leading to dry but humid conditions termed as “October heat.”

Rainfall Distribution

• Annual average rainfall is about 125 cm, with significant variations:
  • High Rainfall Areas: Over 200 cm in parts of the Western Ghats and Northeast India.
  • Medium Rainfall Areas: 100-200 cm in parts of southern Gujarat, Odisha, and the Ganga plains.
  • Low Rainfall Areas: Less than 50 cm in northwestern Rajasthan and parts of the Deccan Plateau.

Global Climate Change

• Impact of Global Warming: Human activities, such as industrialization and greenhouse gas emissions, contribute to global warming, which has severe implications for weather patterns, agriculture, and sea levels across India.
• Future Projections: Climate models indicate a rising temperature trend by 2°C by 2100, impacting monsoonal behavior and increasing the frequency of severe weather events like droughts and floods.

In summary, India's climate is complex and influenced by various factors including geographical location, topography, and seasonal winds it experiences, making its agricultural patterns heavily reliant on monsoon cycles.

1. Weather vs. Climate: Weather refers to short-term atmospheric conditions, while climate represents average conditions over long periods.
2. Monsoon Dynamics: India experiences a monsoonal type of climate, which is critical for agriculture.
3. Temperature Extremes: Temperature varies regionally with extreme highs and lows across different states.
4. Precipitation Levels: Rainfall exhibits drastic variability, with areas like Cherrapunji receiving among the highest amounts.
5. Climate Influencers: Key factors determining climate include latitude, altitude, topography, and distance from the sea.
6. Seasonal Changes: India observes four distinct climatic seasons affecting agriculture and lifestyle.
7. Global Warming Effects: Human activities are leading to global warming, impacting rainfall patterns and sea levels.
8. E.I Niño Influence: Can disrupt the monsoon patterns significantly year-on-year.