🌦 Class 9 Geography – Climate
📚 Chapter: Climate (जलवायु)
📅 Session: 2025–26 | 🏫 Book: NCERT – Social Science Geography
❇️ Climate (जलवायु)
🔹 Definition: Climate refers to the sum total (कुल योग) of weather conditions and variations over a large area for a long period of time (more than 30 years).
☁️ Weather (मौसम)
🔹 Weather refers to the state of the atmosphere (वायुमंडल की स्थिति) over an area at any given point of time.
🔹 Elements of Weather & Climate – Both have the same components:
- 🌡 Temperature (तापमान)
- 🌬 Atmospheric Pressure (वायुदाब)
- 💨 Wind (पवन)
- 💧 Humidity (आर्द्रता)
- 🌧 Precipitation (वृष्टि)
📅 Seasons in India:
- ❄ Winter (शीत ऋतु)
- 🔥 Summer (ग्रीष्म ऋतु)
- 🌧 Rainy Season (वर्षा ऋतु)
🔄 Difference Between Weather & Climate (मौसम और जलवायु का अंतर)
🌬 Monsoon (मानसून)
🔹 Origin: Derived from Arabic word ‘Mausim’ (मौसम) meaning "season".
🔹 Definition: Seasonal reversal in wind direction (पवन की दिशा का परिवर्तन) during a year.
🇮🇳 Climate of India (भारत की जलवायु)
🔹 Described as ‘Monsoon Type’ (मानसूनी प्रकार) – Found mainly in South & Southeast Asia.
🔹 Regional Variations:
- Rajasthan & Gujarat (Western parts) – 🌵 Less than 20 cm rainfall annually.
- Assam & Arunachal Pradesh – 🌧 More than 250 cm rainfall annually.
- Temperature extremes – ❄ Winters in Ladakh below -45°C, 🌴 Thiruvananthapuram around 45°C same night.
💡 Impact: These variations result in different lifestyles (भिन्न जीवनशैली) of people.
🗺 Climatic Controls (जलवायु को नियंत्रित करने वाले कारक)
Six major factors:
1️⃣ Latitude (अक्षांश)
2️⃣ Altitude (ऊँचाई)
3️⃣ Pressure & Wind System (दाब और पवन प्रणाली)
4️⃣ Distance from Sea / Continentality (समुद्र से दूरी)
5️⃣ Ocean Currents (महासागरीय धाराएँ)
6️⃣ Relief Features (स्थलाकृति)
🌏 Factors Affecting Climate of India (भारत की जलवायु को प्रभावित करने वाले कारक)
📍 Main Factors (मुख्य कारक)
- Latitude (अक्षांश)
- Altitude (ऊँचाई)
- Distance from Sea (समुद्र से दूरी)
- Ocean Currents (महासागरीय धाराएँ)
- Relief Features / Landscape (भू-आकृति)
- Pressure and Wind System (दबाव और पवन प्रणाली)
1️⃣ Latitude (अक्षांश) 🌞
- The Tropic of Cancer (कर्क रेखा) passes through India at 23°26’N.
- Passes through 8 Indian states from Rann of Kutch (Gujarat) to Mizoram (East).
- Divides India into two halves:
- North of Tropic of Cancer → Sub-tropical region (उप-उष्णकटिबंधीय क्षेत्र)
- South of Tropic of Cancer → Tropical region (उष्णकटिबंधीय क्षेत्र)
- Tropical areas remain hot throughout the year. 🌡️
2️⃣ Altitude (ऊँचाई) 🏔️
- Temperature decreases as we go higher above sea level.
- Rate: 1°C decrease for every 166 m rise in height.
- Hill stations 🌄 in India are cooler than plains.
3️⃣ Air Pressure & Surface Winds (वायु दाब और सतही पवन) 🌬️
- Weather in India is affected by:
- Pressure & surface winds
- Upper air circulation
- Western cyclonic disturbances & Tropical cyclones
- Air moves from High pressure (Southern Indian Ocean) → crosses Equator → turns right towards Low pressure (Indian subcontinent).
- These are Southwest Monsoon winds (दक्षिण-पश्चिम मानसून पवन) → bring 🌧️ rainfall.
4️⃣ Jet Streams (जेट धाराएँ) ✈️
- Narrow belt of high-altitude winds (ऊँचाई पर तेज़ हवाएँ) at 12,000 m in the troposphere.
- Speed: 110 km/h in summer, 184 km/h in winter.
- Found over 27°–30° N latitude → called Subtropical Westerly Jet Streams.
- Over India:
- Winter → South of Himalayas
- Summer → Move north of Himalayas
- Easterly Jet Stream → Blows over Peninsular India (14°N) in summer.
5️⃣ Western Cyclonic Disturbances (पश्चिमी चक्रवातीय विक्षोभ) 🌪️
- Brought by westerly winds from Mediterranean region.
- Affect North & North-west India during winter months.
- Bring light rain & change in temperature.
🌦 Factors Affecting Climate of India
India’s climate is influenced by multiple geographical and atmospheric factors:
1️⃣ Latitude (अक्षांश)
- Tropic of Cancer (23°26’ N) passes through India from Gujarat’s Rann of Kutch to Mizoram.
- Divides India into two climatic zones:
- North of Tropic → Sub-tropical zone
- South of Tropic → Tropical zone (hot throughout the year)
2️⃣ Altitude (ऊँचाई)
- Temperature decreases with height → 1°C drop for every 166 m rise.
- Hill stations are cooler than plains.
3️⃣ Distance from Sea (समुद्र से दूरी)
- Coastal areas → Moderate climate
- Interior areas → Extreme climate (hot summers, cold winters)
4️⃣ Ocean Currents (महासागरीय धाराएँ)
- Warm & cold ocean currents influence temperature & rainfall.
5️⃣ Relief Features (भौगोलिक स्वरूप)
- Mountains block winds → Himalayas stop cold winds from Central Asia.
- Western Ghats block Arabian Sea monsoon winds.
6️⃣ Pressure & Wind System (वायुदाब और पवन प्रणाली)
- Southwest Monsoon: Winds from high-pressure area of Southern Indian Ocean cross equator & bring rain to India.
- Upper Air Circulation: Movement of jet streams affects monsoon.
💨 Jet Streams (जेट स्ट्रीम)
- Narrow belt of high-altitude (12,000 m) westerly winds.
- Speed: 110 km/h (summer) → 184 km/h (winter)
- Subtropical Westerly Jet → South of Himalayas in winter, shifts north in summer.
- Subtropical Easterly Jet → Over Peninsular India during summer.
🌪 Western Cyclonic Disturbances (पश्चिमी चक्रवाती विक्षोभ)
- Winter weather phenomena from Mediterranean region.
- Bring rain & snow to north and northwest India.
🌧 The Indian Monsoon (भारतीय मानसून)
India has monsoon type climate – strongly affected by seasonal winds.
Factors Influencing Monsoon:
- Difference in heating of land & sea.
- ITCZ (Inter Tropical Convergence Zone) shifts over India.
- High-pressure area near Madagascar.
- Movement of jet streams.
- Southern Oscillation (SO): Reversal of pressure between Pacific Ocean & Indian Ocean (linked with El Niño).
🌊 Onset & Withdrawal of Monsoon
- Onset: Early June in Kerala → Divides into Arabian Sea branch & Bay of Bengal branch.
- Arabian Sea branch → Mumbai by mid-June.
- Bay of Bengal branch → Assam in early June, then deflected to plains.
- Progress: Covers most of India by July.
- Withdrawal:
- Early September → NW India
- Mid-October → South India
- Early December → Entire country
📅 Seasons in India
- Cold Weather Season (Winter) → Mid-Nov to Feb
- Hot Weather Season (Summer) → Mar to May
- Advancing Monsoon (Rainy) → June to Sept
- Retreating Monsoon → Oct to Dec
❄ Cold Weather Season (Winter Season)
- Mid-Nov to Feb.
- Temperature: Decreases from south → north.
- Climate: Warm days, cold nights, frost in north, snow in Himalayas.
- Winds: Northeast trade winds dominate.
High-pressure area in north pushes light winds outward.
☀️ The Hot Weather Season (Summer Season)
📆 Time Period: March to May
- 🌡 Temperature: Northern India experiences rising temperature and falling air pressure.
- 💨 Loo (लू): Strong, gusty, hot & dry winds blowing during the day in north and northwestern India.
- 🌪 Dust Storms: Common; sometimes bring light rain & cool breeze.
- ⚡ Kaal Baisakhi (काल बैशाखी): Localized thunderstorm with violent wind, torrential rain & hail in West Bengal.
- 🥭 Mango Showers: Pre-monsoon showers in Kerala & Karnataka → help in early ripening of mangoes.
🌧 Advancing Monsoon (Rainy Season)
📆 Time Period: June to September
- 🌊 Low pressure over North Indian plains attracts Southeast Trade Winds from southern oceans.
- 💦 Winds bring moisture → heavy rainfall in Western Ghats (up to 250 cm).
- 🌏 Mawsynram (Meghalaya): Wettest place in the world.
- 📉 Rainfall decreases from east to west → Rajasthan & Gujarat get scanty rain.
- ⏳ Monsoon is irregular → dry & wet spells occur.
🍂 Retreating Monsoon
📆 Time Period: October – November
- 💨 Winds weaken & retreat from Northern Plains (early October).
- 🌡 October Heat: Clear skies & rising temperature in plains.
- 🌪 Cyclonic Depressions: Shift of low pressure to Bay of Bengal → cyclones on eastern & southern coasts.
- 🌧 Coromandel Coast Rainfall: Mainly from cyclones & depressions.
🌍 Distribution of Rainfall in India
- 🌧 Very High (400 cm+): Northeastern India & western coast.
- 🌾 Very Low (<60 cm): Western Rajasthan, Gujarat, Punjab, Haryana.
- 🏔 Western Ghats receive more rain than Eastern Ghats (due to moisture loss).
- 🏜 Low rainfall in Eastern Ghats, Deccan Plateau interiors, Leh (J&K).
- 🌊 Eastern states → frequent floods; Western states → drought-like conditions.
🤝 Monsoon as a Unifying Bond
- 🌦 Despite irregularity, monsoon connects the whole country.
- 👨🌾 Farmers eagerly await rainfall → triggers agriculture.
- 🎉 Arrival celebrated with festivals, songs, and dances.
