Climate of India | Aspirant Academy

Study Material

Paper Prelims

PYQ Count 6

1. Southwest monsoon normally sets in over Kerala around 1 June and advances in surges through the Arabian Sea and Bay of Bengal branches.
2. Retreating monsoon gives Tamil Nadu coast its main October-November rainfall, while most of north India is already drying.
3. Western disturbances bring winter rain and snowfall to north-west India and the western Himalaya, helping rabi conditions.
4. Monsoon trough position, Bay lows and active-break cycles explain short-period rainfall distribution across the Ganga plain and central India.
5. Rajasthan's Thar hot arid climate, Aravalli alignment and heat-wave criteria connect national climate mechanisms with state geography.
6. India Meteorological Department, established in 1875, supplies official onset, withdrawal, cyclone, heat-stress and climatological-normal information.

Key facts

Southwest monsoon normally sets in over Kerala around 1 June and advances in surges through the Arabian Sea and Bay of Bengal branches.
Retreating monsoon gives Tamil Nadu coast its main October-November rainfall, while most of north India is already drying.
Western disturbances bring winter rain and snowfall to north-west India and the western Himalaya, helping rabi conditions.
Monsoon trough position, Bay lows and active-break cycles explain short-period rainfall distribution across the Ganga plain and central India.
Rajasthan's Thar hot arid climate, Aravalli alignment and heat-wave criteria connect national climate mechanisms with state geography.

Key Points at a Glance

1
Southwest monsoon normally sets in over Kerala around 1 June and advances in surges through the Arabian Sea and Bay of Bengal branches.
2
Retreating monsoon gives Tamil Nadu coast its main October-November rainfall, while most of north India is already drying.
3
Western disturbances bring winter rain and snowfall to north-west India and the western Himalaya, helping rabi conditions.
4
Monsoon trough position, Bay lows and active-break cycles explain short-period rainfall distribution across the Ganga plain and central India.
5
Rajasthan's Thar hot arid climate, Aravalli alignment and heat-wave criteria connect national climate mechanisms with state geography.
6
India Meteorological Department, established in 1875, supplies official onset, withdrawal, cyclone, heat-stress and climatological-normal information.

How does southwest monsoon onset over Kerala organise India's monsoon branches?

Southwest monsoon onset over Kerala begins India's operational rainy season and sets up the Arabian Sea and Bay of Bengal branches that carry moisture northward and inland.

According to the India Meteorological Department, onset over Kerala can be declared when 60% of the available 14 listed stations report at least 2.5 mm rainfall for two consecutive days, with wind and outgoing-longwave-radiation criteria also satisfied.

IMD Onset Threshold

Normal timing: India Meteorological Department states that the southwest monsoon normally sets in over Kerala around 1 June and advances northwards in surges, usually covering the country around 15 July.
Declaration basis: The onset is declared through rainfall over 14 stations in Kerala and neighbouring areas, wind field and outgoing longwave radiation over the southeast Arabian Sea.
Meaning: This turns a familiar calendar date into a measured meteorological threshold.

Monsoon Branches and Regional Sequencing

Branch / stream	Path and rainfall pattern	Regional effect
Arabian Sea branch	Strikes the Western Ghats and gives heavy windward rainfall.	Kerala, coastal Karnataka and Konkan receive early heavy rain from the Arabian Sea side.
Bay of Bengal stream	Enters through the Bay of Bengal, moves toward the northeast and then bends westward along the Ganga plain.	Assam and Meghalaya receive early intense rain from the Bay side.
Inland advance	Delhi and Rajasthan wait for inland advance.	Rajasthan's connection is indirect but important.

Rajasthan Link

Arabian Sea stream: The Arabian Sea stream crossing Saurashtra and Kutch weakens before reaching western Rajasthan.
Bay branch: The Bay branch loses moisture as rainfall decreases from east to west across the northern plains.
Climate type: The onset date, branch paths, wind reversal and moisture supply together define the monsoon type of Indian climate.

Planning Significance

Delayed or weak branch: A delayed or weak branch affects sowing dates, reservoir inflow, power demand and heat persistence differently in each region.
Onset signal: The onset signal also affects migration of labour, fodder planning and urban water demand in drought-prone districts.
State advisories: The same signal guides state advisories on nursery sowing and contingency cropping.
Exam caution: The onset is therefore a declared meteorological threshold, not a mythic fixed-date arrival; the normal date helps revision, but the official declaration depends on observed rainfall, winds and cloud-top radiation.

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PREDICTED Predicted RAS Questions

Based on PYQ trends and 2026 syllabus analysis

1 MCQ Which statement correctly describes the normal operational start of India's southwest monsoon?

A It normally sets in over Kerala around 1 June. Correct answer
B It normally begins over Tamil Nadu in November.
C It begins with western disturbances over Punjab.
D It starts only after cyclones cross Gujarat.

Explanation

IMD identifies Kerala onset around 1 June as the normal start of the southwest monsoon. Tamil Nadu's main rain is retreating-season rain, western disturbances are winter systems, and Gujarat cyclones are separate coastal hazards.