📖 PART 1: Factors Affecting India's Climate

• Latitude: India lies between 8°N and 37°N. The Tropic of Cancer (23°30'N) divides India — south of it is tropical (hot year-round); north of it is subtropical (distinct seasons).
• Altitude: Temperature decreases ~6.5°C per 1000 m rise. Himalayan regions (Shimla, Darjeeling) are cooler than the plains despite being at the same latitude.
• Distance from the Sea (Continentality): Coastal areas (Mumbai, Chennai) have moderate, equable climate — cool summers, warm winters. Inland areas (Delhi, Jodhpur) have extreme continental climate — very hot summers, cold winters.
• Himalayas: Act as a barrier — (a) prevent cold Siberian winds from entering India (keep winters mild in the plains); (b) force the SW Monsoon to rise and shed rain over India.
• Jet Streams: High-altitude fast-moving air currents (around 12 km altitude). Two important ones for India:
  • Western Jet Stream (subtropical): Brings Western Disturbances (winter rains) across Punjab and northern India.
  • Easterly Jet Stream (tropical): Helps sustain the SW Monsoon over India in summer.
• El Niño: An abnormal warming of the central and eastern Pacific Ocean (every 2–7 years). Results in weaker, delayed, or deficient SW Monsoon over India → drought conditions. E.g., droughts of 1982–83, 2002, 2009 were linked to El Niño.

🌧️ PART 2: Monsoon – Mechanism

Mechanism of the Southwest Monsoon

• Differential Heating: In summer (May-June), the land (especially the Thar Desert and northwestern India) heats up rapidly. A strong low pressure develops over the Indian subcontinent.
• The Indian Ocean remains relatively cooler → high pressure over the ocean.
• Winds blow from high pressure (ocean) to low pressure (land) — bringing moisture-laden sea air inland. This is the SW Monsoon.
• The Intertropical Convergence Zone (ITCZ) shifts northward in summer to approximately 25°N over the Thar Desert — this acts as the "monsoon trough" pulling in moisture-laden winds.

Two Branches of SW Monsoon

Branch	Entry Point	Areas Covered	Key Feature
Arabian Sea Branch	Kerala (around June 1st)	Western Ghats, West Coast, Mumbai, Gujarat, Western MP	Brings very heavy rainfall to Western Ghats (windward side); Deccan Plateau is rain-shadow (dry)
Bay of Bengal Branch	Northeast India (Assam, Meghalaya) around June	Northeast India, Bengal, UP, Delhi, Punjab	Mawsynram/Cherrapunji (Meghalaya) is wettest place — orographic rainfall on Khasi Hills

🗓️ PART 3: Seasons of India

Season	Months	Key Characteristics
Hot Weather / Pre-Monsoon (Summer)	March – May	Very hot; Loo — hot dry winds in North India; Dust storms in Rajasthan; temperature up to 48°C in Thar. Mango Showers in Kerala/Karnataka. Nor'westers / Kalbaisakhi in West Bengal/Assam.
Monsoon (Rainy Season)	June – September	SW Monsoon brings 70–90% of India's annual rainfall. Kerala first to receive (June 1). Highest rainfall: Mawsynram (~11,871 mm/year). Lowest: Jaisalmer (~10 mm/year).
Retreating Monsoon / NE Monsoon	October – November	SW Monsoon withdraws northward, then southeast. Bay of Bengal low-pressure systems bring heavy rain to Coromandel Coast (Tamil Nadu). Cyclones common in Bay of Bengal (Oct–Nov).
Cold Weather (Winter)	December – February	Cold and dry in North India. Western Disturbances (Mediterranean origin) bring winter rainfall to Punjab, Haryana, UP — essential for wheat (rabi crop). South India remains warm and dry.

Key Local Winds and Weather Phenomena

Local Wind / Phenomenon	Description	Region
Loo	Hot, dry, scorching wind blowing in afternoon	Punjab, Haryana, UP, Rajasthan (May–June)
Kalbaisakhi / Nor'westers	Violent thunder-squalls in late afternoon	West Bengal, Assam (April–May). Good for jute & tea.
Mango Showers	Pre-monsoon showers that ripen mangoes	Kerala, Karnataka, Andhra Pradesh
Western Disturbances	Extratropical cyclones from the Mediterranean	Punjab, Haryana, HP, J&K (Dec–Feb); bring winter rain

Distribution of Rainfall in India

• Very heavy (above 200 cm): Western Ghats, Meghalaya, Northeast India, Andaman & Nicobar Islands.
• Heavy (100–200 cm): North Bengal, Coastal Andhra/Odisha, most of Assam.
• Moderate (60–100 cm): Eastern MP, Deccan plateau (interior).
• Low (below 60 cm): Northwest India, Rajasthan, parts of Gujarat, Ladakh.

🌡️ PART 4: Reading and Interpreting Climate Data

• Climate data is presented in graphs (rainfall bar chart + temperature line graph) called climographs or separate bar/line graphs.
• From a temperature graph: identify seasonal pattern; note the month of highest and lowest temperature.
• From a rainfall graph: identify monsoon months; calculate annual total; identify dry and wet months.
• Temperature Range = Maximum Temperature − Minimum Temperature. Large range = continental climate. Small range = equable/maritime climate.

📝 Quick Revision – Key Facts

Topic	Key Fact
Wettest place in India	Mawsynram (Meghalaya) – avg ~11,871 mm/year
Driest place in India	Jaisalmer / Leh area (~10 cm/year)
Monsoon onset (Kerala)	Around June 1st
NE Monsoon area	Tamil Nadu Coromandel Coast (Oct–Nov)
El Niño effect	Weaker monsoon → drought
Loo wind	Hot dry wind; North India; May–June
Kalbaisakhi	Nor'westers; West Bengal; good for jute and tea
Western Disturbances	Mediterranean origin; winter rains Punjab/Haryana; vital for wheat