🌏 India's Climate — Basic Facts
- Word "Monsoon" → from Arabic word "mawsim (mausim)" (Season)
- Monsoon = Seasonal reversal of winds
- India's monsoon → South-West Monsoon (June–September)
- First arrival → Malabar Coast of Kerala
📐 Theories of Monsoon Origin
- Proponent: Edmund Halley (1686 AD)
- Origin: Unequal heating of land and water
- Gives: Winter Monsoon + Summer Monsoon
- Proponent: Flohn
- Origin: Convergence of trade winds near the equator
- Upper troposphere near the tropopause; both hemispheres
- Average Speed: 150–200 km/h
- Core Speed: 320–480 km/h
- Width of belt: A few hundred km
- Vertical depth: 2–3 km wide
⭐ Key Climate Facts
Mawsynram
Wettest Place in World (Meghalaya)
Leh
Extremely Dry Cold-Desert Example (Ladakh)
NW India
Among last covered: western Rajasthan–Haryana–Punjab
Punjab
Both monsoon branches converge and reinforce rainfall
🚨 EXAM TRAP
- Monsoon = Arabic "mawsim (mausim)" — NOT Hindi/Sanskrit word
- Thermal Concept = Edmund Halley (1686) | Dynamic = Flohn
- Both monsoon branches converge over Punjab Plains
- Mawsynram = world's wettest | Cherrapunji = Meghalaya; among the world's wettest, with exceptional historical rainfall records
🌧️ South-West Monsoon — June to September
- Type: South-West Monsoon
- Period: June to September
- First Arrival: Malabar Coast of Kerala
- Both branches converge over: Punjab Plains
🌊 Two Branches of Monsoon
🌊 Bay of Bengal Branch
- Flows northward
- Hits Garo, Khasi, Jaintia Hills
- Myanmar / southeast Bangladesh → West Bengal–Bangladesh → Ganga plains & Brahmaputra valley
- Heavy Rainfall
- Mawsynram = world's highest rainfall
🌬️ Arabian Sea Branch
- Flows parallel to Western Ghats
- First rainfall on Kerala
- Coastal plain: >250 cm
- 3 sub-branches:
- Western Ghat Branch
- Narmada & Tapi Valley Branch
- Aravalli Parallel Branch
🌸 Pre-Monsoon Rains / Local Names
| Name |
Region |
Benefit |
| Bordoi Chilla |
Assam (local name) |
Tea cultivation |
| Kal Baisakhi |
Eastern India — WB, Bihar, Jharkhand, Odisha |
Tea, Jute, Rice |
| Cherry Blossom |
Kerala + Karnataka |
Coffee flower blooming |
| Mango Shower |
Kerala and coastal Karnataka |
Mango ripening |
- No rainfall after few days during monsoon season
- Rain-bearing storms/depressions become infrequent along the monsoon trough
- Shift in ITCZ (Inter-Tropical Convergence Zone)
- Return/withdrawal of monsoon
- Type: North-East Monsoon
- Withdraws from Northern Plains
- Period: October – November
- Rainfall on Coromandel Coast (Tamil Nadu)
🚨 EXAM TRAP
- Kal Baisakhi = Bihar, WB, Jharkhand, Odisha — NE India pre-monsoon rains
- Bordoisila is the local Assamese name associated with the same pre-monsoon nor'wester phenomenon.
- TN rain in Oct-Nov = North-East Monsoon (NOT SW monsoon)
- The Coromandel Coast along eastern Tamil Nadu receives most of its rainfall from the retreating or northeast monsoon.
- Arabian Sea branch has 3 sub-branches (Bay of Bengal branch = direct northward)
📅 Four Seasons of India
- Period: Mid-November to February
- Wind: Land → Sea
- Night: longer | Day: shorter
- Rainfall type: Mawath (Western Disturbances)
- NE Monsoon → rainfall in Tamil Nadu
- Western disturbances = temperate cyclonic systems from the eastern Mediterranean, moving across West Asia to NW India
- Beneficial for: Rabi crops
- Period: March–May; into early June in parts of north India
- Temperature: 30°–40°C
- Wind: Sea → Land
- Hot wind: Loo
- Loo blows from Punjab to Bihar region
- Period: June to September
- Maximum rainfall by South-West Monsoon
- Period: October to November
- Season of monsoon retreat
- Cyclonic storms originate in Bay of Bengal
📅 Six Seasons — Indian Calendar
| Season (Ritu) |
Indian Months |
English Months |
|
Vasant (Spring) |
Chaitra – Baisakh |
March – April |
|
Grishma (Summer) |
Jyeshtha – Ashadha |
May – June |
|
Varsha (Monsoon) |
Shravan – Bhadrapada |
July – August |
|
Sharad (Autumn) |
Ashwin – Kartik |
September – October |
|
Hemant (Pre-Winter) |
Margashirsha – Pausha |
November – December |
|
Shishir (Winter) |
Magha – Phalguna |
January – February |
- Hot dry wind: Loo
- Blows from: Punjab to Bihar
- Season: Summer (March–June)
- Temperature can cross 45°C during Loo
- The hot, dry loo winds also affect Bihar during summer.
⚡ QUICK RECALL — 6 Seasons in Order
Vasant → Grishma → Varsha → Sharad → Hemant → Shishir
(Spring → Summer → Monsoon → Autumn → Pre-Winter → Winter)
🚨 EXAM TRAP
- Mawath refers to winter rainfall in Rajasthan caused by western disturbances.
- Loo = summer hot wind = Punjab to Bihar — NOT south India
- Tamil Nadu receives substantial monsoon rainfall in October and November during the retreating-monsoon season.
- Western Disturbances = temperate cyclonic systems originating around the eastern Mediterranean; winter rain in NW India benefits Rabi crops
💧 Rainfall Regions of India
| Region |
Rainfall |
Areas |
| High Rainfall |
>200 cm |
Western Coast, Western Ghats, NE Sub-Himalayan region, Meghalaya Hills |
| Moderate Rainfall |
100–200 cm |
S.Gujarat, E.Tamil Nadu, Odisha, NE Peninsula, Jharkhand, Bihar, E.MP, N.Ganga Plains
near Sub-Himalaya, Cachar Valley, Manipur |
| Low Rainfall |
50–100 cm |
W.UP, Delhi, Haryana, Punjab, J&K, E.Rajasthan, Gujarat, Deccan |
| Scanty Rainfall |
<50 cm |
AP, some parts of Karnataka & Maharashtra, Ladakh, W.Rajasthan (most) |
- Bihar falls in Moderate Rainfall Region → 100–200 cm
- Pre-monsoon: Kal Baisakhi (Norwester) brings rains
- Main season: SW Monsoon (June–Sept)
- River floods (Kosi, Ganga, Gandak) augment water availability
- Winter: Western Disturbances bring minimal rainfall
🌧️ Special Rainfall Facts
-
Mawsynram — World's wettest
- Cherrapunji — among the world's wettest; exceptional historical rainfall records (Meghalaya)
- High due to Khasi Hills funnel effect
- Leh — classic extremely dry cold-desert example
- Ladakh (rain shadow of Himalaya)
- Very cold desert climate
- Northwest India
- Western Rajasthan–Haryana–Punjab are among the last areas covered by the SW monsoon.
🚨 EXAM TRAP
- Bihar = Moderate rainfall (100–200 cm) — NOT high or low
- Ladakh = Scanty (cold desert) | W. Rajasthan = Scanty (hot desert)
- W. Ghats = High (>200cm) | Eastern side of W.Ghats = Rain Shadow → Low
- Mawsynram = world's wettest (Meghalaya) — NOT Cherrapunji (both close)
🗺️ Köppen's Climate Classification — India
| Köppen Code |
Climate Type |
Region in India |
| Amw |
Tropical Monsoon — Short Dry Season |
Western coastal region, especially south of Goa |
| Aw |
Tropical Savanna Climate |
Most Peninsular Plateau, excluding main west-coast and Coromandel strips; parts of Jharkhand and WB |
| BShw |
Semi-Arid Steppe Climate |
NW Gujarat, E.Rajasthan, W.Haryana; Rain shadow of Karnataka & TN |
| Bwhw |
Hot Desert Climate |
Extreme W.Rajasthan, N.Gujarat, S.Haryana |
| Cwg |
Monsoon — Dry Cold Winter |
Ganga Plains |
| Dfc |
Moist Winter — Short Summer |
Sikkim, Arunachal Pradesh and parts of Assam |
| E (Mountain) |
Polar / Mountain Climate |
Hill regions of J&K + Himachal Pradesh |
| ET (Tundra) |
Tundra-like Climate |
Hill regions of Uttarakhand |
- India = Tropical Monsoon Climate
- Monsoon = Arabic mawsim (mausim)
- Thermal concept = Edmund Halley (1686)
- Dynamic concept = Flohn
- SW Monsoon = June–September
- First on: Malabar Coast, Kerala
- Both branches meet: Punjab
- El Niño = warm central/eastern equatorial Pacific; often weaker Indian monsoon tendency
- La Niña = cool central/eastern equatorial Pacific; often stronger Indian monsoon tendency
- Kal Baisakhi = Bihar, WB, JH, Odisha
- Loo = hot wind = Punjab to Bihar
- Mawath = winter rain = Rajasthan
- NE Monsoon = TN = Oct–Nov
- Mawsynram = world's wettest | Leh = extremely dry cold-desert example
- Bihar rainfall = 100–200 cm (Moderate)
- Ganga Plains = Cwg (Köppen) — dry cold winter
- Köppen: Cwg (Ganga Plains — Monsoon type with dry cold winter)
- Rainfall: 100–200 cm (Moderate)
- Pre-Monsoon: Kal Baisakhi / Norwester
- Summer hot wind: Loo (from Punjab)
- Winter rain: from Western Disturbances (Rabi crops)
- Jharkhand = Aw (Tropical Savanna) — near Bihar
🚨 EXAM TRAP — Köppen
- The Ganga Plain, including Bihar, falls under the Cwg climatic type in the Köppen classification used here.
- Hot Desert (Bwhw) = only extreme W.Rajasthan — NOT all Rajasthan
- Tundra-like (ET) = Uttarakhand | Mountain (E) = J&K + HP
- The tropical savanna (Aw) climatic belt includes parts of Jharkhand and West Bengal adjoining Bihar.