Weather vs. Climate

• Weather refers to the daily or short-term conditions of the atmosphere, such as temperature, humidity, precipitation, and wind. Weather can change from hour to hour and day to day.
• Climate is the average weather over a long period (usually 30 years or more) for a specific area. It defines the general atmospheric conditions that prevail over regions and is more stable than weather.

India’s climate varies significantly across regions, ranging from the tropical climate in the south to the temperate climate in the north.

Factors Influencing India’s Climate

India’s climate is shaped by several factors:

Latitude

The Tropic of Cancer passes through the middle of India, dividing it into two zones:

• Tropical Zone: South of the Tropic of Cancer, where temperatures remain high throughout the year with minimal seasonal variation.
• Temperate Zone: North of the Tropic of Cancer, which experiences more distinct seasons with cooler winters and hotter summers.

Himalayan Mountains

• The Himalayas block cold winds from Central Asia, which keeps northern India warmer during winter.
• The mountain range also traps moisture-laden monsoon winds, forcing them to release precipitation over northern and eastern India.

Land and Sea Distribution

• India is surrounded by the Indian Ocean, Arabian Sea, and Bay of Bengal on three sides, creating a maritime influence. Coastal regions have a moderate climate, while the interior experiences continental climate with more extreme temperatures.
• The land heats up faster than the sea during summer, causing low pressure over land and drawing in moist oceanic winds, leading to the monsoon.

Altitude

• Altitude influences temperature; for every 1000 meters increase in altitude, temperature drops by about 6.5°C.
• High-altitude areas like the Himalayas and hill stations like Shimla are cooler than regions at sea level, such as Chennai or Mumbai.

Relief and Topography

• Mountain ranges like the Western Ghats force moist winds to rise, causing orographic rainfall on the windward side while creating rain shadows on the leeward side.
• Regions like Ladakh and parts of the Deccan Plateau remain dry due to rain shadow effects.

The Monsoon System

India’s climate is heavily influenced by the monsoon winds, which are seasonal winds that reverse direction between summer and winter.

Southwest Monsoon (June to September)

• As the land heats up during summer, a low-pressure zone forms over northern India, drawing in moist winds from the Indian Ocean.
• The monsoon winds are deflected by the Coriolis Effect, causing them to blow from the southwest.
• Arabian Sea Branch:
  • First reaches the Western Ghats, causing heavy rainfall on the west coast (e.g., Kerala and Konkan Coast).
  • As it moves further inland, rainfall decreases, creating a rain shadow on the Deccan Plateau.
• Bay of Bengal Branch:
  • Moves toward northeast India, resulting in heavy rainfall over Assam and West Bengal.
  • The branch divides, with one part moving westward to cover the Gangetic Plains and another turning north toward the Himalayas, where it delivers heavy rain to places like Cherrapunji, one of the wettest places on Earth.

Retreating Monsoon (October to November)

• By October, the sun shifts southward, and temperature over land decreases. This creates a high-pressure zone over northern India, pushing the monsoon winds back.
• Northeast Monsoon:
  • Winds blow from the northeast, bringing rain mainly to Tamil Nadu and parts of Andhra Pradesh.
  • Cyclones in the Bay of Bengal during this period can cause heavy rainfall and coastal flooding in southeastern India.

Seasonal Climate Variations in India

India has four main seasons, each with distinct characteristics:

Cold Weather Season (Winter) – December to February

• North India experiences its coldest temperatures, often between 5°C and 15°C.
• The Western Disturbances, originating in the Mediterranean region, bring occasional rain and snowfall to northwestern India, particularly in Punjab, Himachal Pradesh, and Jammu & Kashmir.

Hot Weather Season (Summer) – March to May

• High temperatures are common, especially in northwestern India, where temperatures often exceed 40°C.
• Local winds include:
  • Loo: Hot, dry winds blowing across the Gangetic Plain, causing heatwaves.
  • Kalbaisakhi: Violent thunderstorms in West Bengal and Assam that bring short bursts of rain and hail.

Southwest Monsoon Season (Rainy Season) – June to September

• Most of India’s rainfall occurs during this period, with regions like Cherrapunji and Mawsynram receiving over 11,000 mm of rain annually.
• Regional Variations: While coastal and northeast areas receive heavy rainfall, regions like Rajasthan receive limited monsoon rains, leading to semi-arid conditions.

Retreating Monsoon Season (Autumn) – October to November

• The retreating monsoon brings clear skies and slightly cooler temperatures.
• The withdrawal of moisture-laden winds leaves high humidity in the air, often referred to as October Heat.
• Tamil Nadu receives significant rainfall during this season due to the northeast monsoon winds.

The Impact of the Monsoon on India

The monsoon is critical to India’s economy and affects multiple aspects of life:

• Agriculture: Monsoon rains support rainfed agriculture, crucial for rice, wheat, and pulses. About 60% of India’s agriculture relies on monsoon rainfall.
• Water Resources: Monsoons replenish groundwater and rivers, providing drinking water and supporting irrigation.
• Hydropower: The monsoon contributes to the filling of dams and reservoirs, essential for hydropower generation.
• Impact on Economy: A good monsoon boosts agriculture and reduces dependency on water from rivers and reservoirs, while a weak monsoon can lead to droughts, impacting food supply and economic stability.

Regional Climate Variations

India’s climate varies significantly across regions, even during the monsoon:

• Western India (e.g., Rajasthan) has an arid climate with low rainfall.
• Northeast India and the Western Ghats receive heavy rainfall due to orographic effects.
• Coastal Regions experience moderate temperatures year-round, while inland areas see more extreme temperature variations.
• Himalayan Regions have cold, snow-laden winters and cool summers, while peninsular regions have warmer winters and minimal temperature variation.

Conclusion

India’s climate is a complex system shaped by geographical features, ocean currents, seasonal winds, and monsoons. These elements influence the agriculture, water availability, and daily life across the country. Understanding these dynamics is essential for managing resources, preparing for seasonal variations, and planning for the future.