Climate of India: Monsoon, Seasons and Climate Graphs, ISC Class 12

What Climate is about

Weightage: CISCE publishes no chapter or unit weightage for ISC Geography. Climate is part of 1. Physical Environment (iii) of the 2027 syllabus and can be asked anywhere in the 70-mark Paper I (Section A one-mark and map items, Section B 4-mark short answers, Section C 7-mark long answers).Source: CISCE ISC Geography (853) syllabus, examination year 2027; ISC 2027 specimen question paper

Key concepts

Factors affecting India's climate

1. Latitude: the Tropic of Cancer divides India into a tropical south (high temperatures all year, small range) and a subtropical north (hot summers, cold winters, large range).
2. Northern mountains: the Himalayas block cold winds from Central Asia in winter and trap the monsoon winds, forcing them to shed rain over the north.
3. Distance from the sea: coastal places have an equable (maritime) climate with a small annual range of temperature; interior places have a continental (extreme) climate with a large range.
4. Relief (physiography): the Western Ghats cause heavy rain on their windward side and a rain shadow on the Deccan; the Aravallis lie parallel to the Arabian Sea branch, so Rajasthan gets little rain.
5. Monsoon winds: the seasonal reversal of winds controls the rhythm of seasons.
6. Upper air circulation (jet streams): the westerly jet stream south of the Himalayas in winter and the easterly jet over the Peninsula in summer influence the monsoon's onset and withdrawal.
7. Western disturbances: low-pressure systems from the Mediterranean that bring winter rain and snow to north-west India, useful for wheat.
8. Tropical cyclones: form over the Bay of Bengal and Arabian Sea, especially in the retreating monsoon season, bringing heavy rain and storms to the east coast.
9. Southern Oscillation and El Nino: changes in pressure between the eastern and western Pacific and warming of the eastern Pacific (El Nino) are often linked to weak monsoons and droughts in India.

Worked example

[2] Explain how the Himalayas influence the climate of India. (Understand)

Try it first, then show the solutionSolution

1. They block cold, dry winds from Central Asia, keeping north India warmer in winter - 1 mark.
2. They trap the south-west monsoon winds, causing rain over north India and making the subcontinent a distinct climatic unit - 1 mark.

Answer: The Himalayas protect India from the bitterly cold winds of Central Asia in winter, and they act as a barrier to the south-west monsoon winds, forcing them to rise and give rain over northern India; as a result the whole subcontinent has a distinct monsoon climate.

Origin and mechanism of the monsoon

The monsoon is a seasonal reversal of winds and the rainfall that comes with it.

Mechanism
1. Differential heating: in summer the land heats up faster than the sea. Intense heat over north-west India and Pakistan creates a low-pressure area, while high pressure lies over the Indian Ocean.
2. Shift of the ITCZ: the Inter-Tropical Convergence Zone moves north over the Ganga plain in summer (the monsoon trough).
3. Winds: the south-east trade winds of the southern hemisphere cross the equator, are deflected to the right by the Earth's rotation and become the south-west monsoon, laden with moisture.
4. Jet streams: the westerly jet stream shifts north of the Himalayas in early summer and an easterly jet appears over the Peninsula; this is associated with the sudden onset ('burst') of the monsoon in early June.
5. Tibetan Plateau heating creates high pressure aloft that strengthens the easterly jet.
6. Branches: the Arabian Sea branch strikes the Western Ghats and moves north; the Bay of Bengal branch moves to the north-east, is deflected by the Himalayas and moves west up the Ganga plain.
7. Retreat: from September the land cools, the low pressure weakens and the winds withdraw south-eastwards; by winter the north-east monsoon blows from land to sea.

Southern Oscillation: a see-saw of pressure between the Indian Ocean and the Pacific; when pressure is higher over the Indian Ocean than the Pacific, the monsoon tends to be weak, and El Nino years are often drought years.

Worked example

[4] Explain the origin and mechanism of the south-west monsoon. (Understand)

Try it first, then show the solutionSolution

1. Land heats faster than sea; low pressure over north-west India, high pressure over the ocean - 1 mark.
2. The ITCZ shifts north; south-east trades cross the equator and become south-west winds - 1 mark.
3. Westerly jet moves north of the Himalayas, easterly jet over the Peninsula; sudden burst in June - 1 mark.
4. Two branches: Arabian Sea and Bay of Bengal; Himalayas trap the winds - 1 mark.

Answer: In summer the land heats much faster than the sea, creating low pressure over north-west India and high pressure over the Indian Ocean, while the ITCZ moves north. The south-east trade winds cross the equator, are deflected and blow as the moist south-west monsoon. When the westerly jet stream shifts north of the Himalayas and an easterly jet forms over the Peninsula, the monsoon 'bursts' in early June. It advances in two branches, from the Arabian Sea and the Bay of Bengal, and the Himalayas trap the winds so that they shed rain over the subcontinent.

The four seasons

1. Cool and dry season (winter, December-February)

• Temperature: decreases from south to north; the south stays warm (above 20 °C) while the north is cold, with frost in places.
• Pressure: high pressure over north-west India; winds blow from land to sea (north-east monsoon).
• Rainfall: generally dry, but western disturbances bring rain and snow to north-west India, and the north-east monsoon brings rain to the Tamil Nadu coast.

2. Hot and dry season (summer, March-May)

• Temperature: rises from south to north; north-west India exceeds 40-45 °C; the south is moderated by the sea.
• Pressure: low pressure develops over north-west India.
• Winds and weather: hot, dry 'loo' winds in the north; dust storms; local thunderstorms: Kalbaisakhi (Nor'westers) in West Bengal and Assam, mango showers in Kerala and Karnataka, cherry blossom showers in Karnataka.

3. Hot and wet season (south-west monsoon, June-September)

• Temperature: high but lowered by cloud and rain.
• Pressure: deep low over north-west India (monsoon trough).
• Rainfall: about three-quarters of India's annual rain; heavy on the Western Ghats and the north-east, decreasing towards the north-west; breaks in the monsoon are common.

4. Cool and wet season (retreating monsoon, October-November)

• Temperature: falls gradually; 'October heat' due to high temperature and humidity.
• Pressure: the low shifts to the Bay of Bengal.
• Rainfall: the monsoon withdraws; tropical cyclones from the Bay of Bengal and the north-east monsoon bring heavy rain to the Coromandel coast (Tamil Nadu), Andhra Pradesh and Odisha.

Worked example

[4] Describe the conditions of the cool and wet (retreating monsoon) season. (Understand)

Try it first, then show the solutionSolution

1. October-November; the monsoon withdraws as land cools - 1 mark.
2. Low pressure shifts to the Bay of Bengal; 'October heat' from heat and humidity - 1 mark.
3. Tropical cyclones form in the Bay of Bengal - 1 mark.
4. Heavy rain on the Coromandel coast from the north-east monsoon and cyclones - 1 mark.

Answer: In October and November the land cools and the south-west monsoon withdraws. The low-pressure area moves to the Bay of Bengal, and high temperature with humidity causes 'October heat'. Tropical cyclones develop over the Bay of Bengal, and together with the north-east monsoon they bring heavy rain to the Coromandel coast of Tamil Nadu and to Andhra Pradesh and Odisha.

Rainfall distribution, variability, droughts and floods

Distribution
1. Very heavy (over about 200 cm): the Western Ghats coast, Meghalaya and the north-east (Mawsynram and Cherrapunji among the wettest places in the world), the Andaman and Nicobar Islands.
2. Moderate (100-200 cm): eastern India, the Ganga plain east of Delhi, parts of the eastern Peninsula.
3. Low (50-100 cm): the interior Deccan (rain shadow), western Uttar Pradesh, Punjab, Haryana, eastern Rajasthan.
4. Very low (below 50 cm): western Rajasthan, Kachchh, Ladakh.

Variability: the year-to-year change in rainfall; it is high where rainfall is low (above 50 per cent in western Rajasthan) and low where rainfall is high (the Western Ghats coast, the north-east). High variability makes farming risky.

Droughts: caused by a delayed onset, long breaks or early withdrawal of the monsoon, often in El Nino years; drought-prone areas include Rajasthan, Gujarat, the interior Deccan and parts of Odisha.

Floods: caused by very heavy rain, cyclones and silted riverbeds; flood-prone areas include the Brahmaputra and Ganga plains (Assam, Bihar, West Bengal) and the deltas of the east coast.

Worked example

[2] What is meant by variability of rainfall? Where is it highest in India? (Understand)

Try it first, then show the solutionSolution

1. Variability is the departure of rainfall from its average from year to year - 1 mark.
2. It is highest in areas of low rainfall such as western Rajasthan and Kachchh - 1 mark.

Answer: Variability of rainfall is the extent to which a place's rainfall in a given year differs from its long-term average. It is highest where rainfall is lowest, as in western Rajasthan and Kachchh, which makes these areas prone to drought.

Reading the five station graphs

How to read a climate graph: look at (1) the annual range of temperature (hottest month minus coldest month), (2) the total rainfall and (3) the months of maximum rain.

1. Mumbai (west coast): small annual range of temperature (about 5-6 °C) because of the sea; very heavy rain (over 200 cm) in June-September from the Arabian Sea branch; dry rest of the year. Maritime, tropical monsoon climate.
2. Delhi (interior north): large range (very hot May-June, cool January); moderate rain (about 70-80 cm), mainly July-August from the Bay of Bengal branch, some winter rain from western disturbances. Continental (extreme) climate.
3. Chennai (east coast): small range (high temperature all year); little rain in June-July because it lies in the rain shadow of the Arabian Sea branch and the Bay of Bengal branch blows parallel to the coast; maximum rain in October-November from the north-east monsoon and cyclones. Maritime climate.
4. Jaisalmer (western Rajasthan): very hot summers, cool winters, large range; scanty rain (about 20 cm or less), because the Arabian Sea branch passes parallel to the Aravallis and the Bay of Bengal branch is exhausted by the time it arrives. Hot desert climate.
5. Leh (Ladakh): very cold winters (below freezing), mild summers; very large range; very little rain (about 10 cm), because it lies in the rain shadow of the Himalayas; some snowfall. Cold desert climate.

Worked example

[2] A station receives little rain in June and July but heavy rain in October and November. Name the station and give a reason for each feature. (Analyse)

Try it first, then show the solutionSolution

1. Station: Chennai; June-July dry because it is in the rain shadow of the Arabian Sea branch and the Bay of Bengal branch blows parallel to the coast - 1 mark.
2. October-November rain from the north-east monsoon and Bay of Bengal cyclones - 1 mark.

Answer: Chennai. In June-July it gets little rain because it lies in the rain shadow of the Western Ghats for the Arabian Sea branch, and the Bay of Bengal branch blows parallel to the Coromandel coast. In October-November it gets heavy rain from the north-east monsoon and tropical cyclones from the Bay of Bengal.

Climate in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Factors Affecting India's Climate and the Mechanism of the Monsoon
• Four Seasons, Rainfall Distribution, Droughts and Floods in India
• Temperature and Rainfall Graphs of Mumbai, Delhi, Chennai, Jaisalmer and Leh

Climate: key facts

Annual range of temperature

Highest monthly mean - lowest monthly mean

Small = maritime; large = continental.

Four seasons

$Cool-dry(Dec-Feb),hot-dry(Mar-May),hot-wet(Jun-Sep),cool-wet(Oct-Nov)$

As named in the syllabus.

Monsoon branches

Arabian Sea branch; Bay of Bengal branch

Burst in early June.

Local storms

Loo (north), Kalbaisakhi (Bengal, Assam), mango showers (Kerala, Karnataka)

Hot-dry season.

Five stations

Mumbai (wet, maritime), Delhi (continental), Chennai (Oct-Nov rain), Jaisalmer (hot desert), Leh (cold desert)

Read range, total and timing.

How the board asks Climate

The question patterns to expect, and the method that works for each.

Tricks to remember Climate

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Factors: 'LaMDa ReMJet WeSE'

  Latitude, Mountains, Distance from sea, Relief, Monsoon winds, Jet streams, Western disturbances, Southern Oscillation, El Nino.

  Use it when: Factors list.

• Seasons: 'CD-HD-HW-CW'

  Cool-dry, Hot-dry, Hot-wet, Cool-wet in calendar order from December.

  Use it when: Sequence of seasons.

• Chennai's odd rain

  'Chennai waits for the north-east'.

  Use it when: Station graph questions.

Climate: board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section D style)

Read the situation, then answer every part. In the board paper this is a 7-mark question split into 1 + 2 + 2 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Climate

The slips examiners see most often, and what to write instead.

• ✗Mistake: Identifying the coastal station without a reason; only naming the sea

  CISCE examiners' comments, 2024: candidates 'Identified the station but could not state the reason', 'Mentioned only the Arabian Sea branch without naming the monsoon wind' and 'Most gave incorrect reasons for scanty rainfall at Y'.

  ✓Do this: Reason = small annual range; source = south-west monsoon (Arabian Sea branch); dryness = parallel Aravallis or distance from the sea.

  Usually costs: Up to 3 marks.

• ✗Mistake: Writing 'retreating monsoon' for Chennai's October-November rain

  CISCE examiners' comments, 2025: candidates 'Wrote retreating monsoon instead of north-east monsoon for Oct-Nov rainfall', 'Did not explain rain shadow and the wind causing it accurately' and 'Did not relate the graph to Chennai'.

  ✓Do this: Chennai: rain shadow in June-July; north-east monsoon and cyclones in October-November.

  Usually costs: 1-2 marks.

• ✗Mistake: Not knowing continental versus maritime

  CISCE examiners' comments, 2025: 'Few attempted; responses showed lack of understanding of the terms continental and maritime'.

  ✓Do this: Compute the annual range: small = maritime; large = continental.

  Usually costs: 2 marks.

• ✗Mistake: Not linking a cyclone report to climatic conditions

  CISCE examiners' comments, 2025: candidates 'Lacked clear understanding of the climate of India' and 'Could not correlate the passage with the question'; others 'Included Odisha although it was given in the question'.

  ✓Do this: Explain ITCZ shift, warm Bay of Bengal, low pressure, humidity; name states other than the one in the passage.

  Usually costs: Up to 4 marks.

Practice questions on Climate

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · Very short answerBoard level

   What are western disturbances?

   Hint

   Mediterranean origin.

   Answer

   Low-pressure systems from the Mediterranean region that bring winter rain and snow to north-west India.

2. Q2 · 1 mark · MCQBoard level

   Which local storm is called Kalbaisakhi?
   (a) Loo
   (b) Nor'wester
   (c) Mango shower
   (d) Western disturbance

   Hint

   Bengal.

   Answer

   (b) Nor'wester.

3. Q3 · 1 mark · Very short answerHarder board level

   Why does Leh receive very little rain?

   Hint

   Behind the Himalayas.

   Answer

   It lies in the rain shadow of the Himalayas, far from the monsoon winds.

4. Q4 · 1 mark · Very short answerHarder board level

   What is 'October heat'?

   Hint

   Heat plus humidity.

   Answer

   Oppressive weather in October caused by high temperature and high humidity after the monsoon withdraws.

5. Q5 · 2 marks · Short answerBoard level

   [2] Why does Delhi have a continental climate?

   Hint

   Distance from sea.

   Answer

   Delhi lies far inland, away from the moderating influence of the sea, so it has very hot summers and cold winters, with a large annual range of temperature.

6. Q6 · 4 marks · Short answerHarder board level

   [4] Describe the conditions of the cool and dry season in north and south India.

   Hint

   Temperature, pressure, winds, rain.

   Answer

   (1) Temperature falls from south to north: the south stays warm, the north is cold with frost in places. (2) High pressure builds over north-west India, and winds blow from land to sea as the north-east monsoon. (3) The weather is mainly dry. (4) Western disturbances bring rain and snow to the north-west, and the north-east monsoon brings rain to the Tamil Nadu coast.

7. Q7 · 4 marks · Short answerHOTS / competency

   [4] Explain why rainfall variability is a problem for Indian agriculture.

   Hint

   Dependence, timing, droughts, floods.

   Answer

   (1) Most farming depends on monsoon rain, so a weak monsoon reduces output. (2) A delayed onset or long breaks disturb sowing and crop growth. (3) High variability in dry regions causes frequent droughts. (4) Excess rain in some years causes floods that destroy crops; hence irrigation and drought-resistant crops are needed.

8. Q8 · 4 marks · Short answerHOTS / competency

   [4] Explain the role of jet streams in the Indian monsoon.

   Hint

   Winter westerly, summer easterly.

   Answer

   (1) In winter a westerly jet stream flows south of the Himalayas, bringing western disturbances and keeping the monsoon away. (2) In early summer it shifts north of the Himalayas. (3) An easterly jet then forms over the Peninsula. (4) This change is linked to the sudden burst of the monsoon in June; the reverse shift in autumn marks its withdrawal.

9. Q9 · 7 marks · Long answerHOTS / competency

   [7] (a) Explain four factors that affect the climate of India. [4]
   (b) Compare the climates of Mumbai and Delhi using their graphs. [3]

   Hint

   (a) latitude, Himalayas, sea, relief; (b) range, total, timing.

   Answer

   (a) Latitude divides India into a tropical south and subtropical north; the Himalayas block cold winds and trap the monsoon; distance from the sea gives the coast an equable climate and the interior an extreme one; relief such as the Western Ghats causes heavy rain on the windward side and a rain shadow inland. (b) Mumbai has a small annual range (about 5-6 °C) while Delhi's is large; Mumbai gets over 200 cm of rain from the Arabian Sea branch while Delhi gets about 70-80 cm, mainly in July-August from the Bay of Bengal branch; Mumbai's climate is maritime, Delhi's continental.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.In which months does Chennai get its maximum rain?Show answer

   October and November.

2. 2.What is the ITCZ?Show answer

   The Inter-Tropical Convergence Zone, a low-pressure belt where trade winds meet; it shifts north over India in summer.

3. 3.Name two of the wettest places in India.Show answer

   Mawsynram and Cherrapunji (Meghalaya).

4. 4.Which winds bring winter rain to north-west India?Show answer

   Western disturbances.

5. 5.What is a 'break' in the monsoon?Show answer

   A dry spell of several days or weeks during the rainy season.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Factors: latitude, Himalayas, sea, relief, monsoon winds, jet streams, western disturbances, cyclones, Southern Oscillation, El Nino.
• ☐Monsoon: differential heating, ITCZ shift, south-west winds, jet streams, burst, two branches, retreat.
• ☐Seasons: cool-dry (Dec-Feb), hot-dry (Mar-May), hot-wet (Jun-Sep), cool-wet (Oct-Nov).
• ☐Rain: heavy on Western Ghats and north-east; scanty in western Rajasthan and Ladakh; variability highest where rain is lowest.
• ☐Stations: Mumbai maritime and wet; Delhi continental; Chennai Oct-Nov rain; Jaisalmer hot desert; Leh cold desert.

Climate: frequently asked questions