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Class 11 Climate: cheat sheet
CBSE Social Science. What controls India’s climate, how the monsoon works, the four seasons, local storms and winds, and how rainfall is spread across the country.
Key ideas
- India’s climate is controlled by latitude, the Himalayas, the spread of land and water, distance from the sea, altitude and relief.
- In summer the ITCZ moves north over the Ganga plain; south-east trades cross the equator, turn south-west and arrive as the monsoon with a sudden “burst”.
- The monsoon has two branches: the Arabian Sea branch drenches the Western Ghats, and the Bay of Bengal branch moves up the Ganga and Brahmaputra valleys.
- Meteorologists recognise four seasons: cold weather, hot weather, south-west monsoon, and the retreating monsoon with its “October heat”.
- Local storms and winds: mango showers and blossom showers in the south, nor’westers (kalbaisakhi) in Bengal, and the hot, dry loo over the northern plains.
- Tamil Nadu gets most of its rain from the north-east monsoon; winter rain from western disturbances helps rabi crops in the north-west.
- A break in the monsoon is a dry spell of a week or more during the rainy season.
Remember
| Onset | Kerala coast by about 1st June; the whole country by mid-July |
| Average annual rainfall | about 125 cm |
| Rainfall categories | high over 200 cm; medium 100–200 cm; low 50–100 cm; inadequate under 50 cm |
| Date of onset elsewhere | 1st June + number of days (June has 30 days) |
| Range of temperature | higher − lower (subtract a minus figure by adding it) |
| Wettest place | Mawsynram |
| Traditional seasons | Vasanta Mar–Apr, Grishma May–Jun, Varsha Jul–Aug, Sharada Sep–Oct, Hemanta Nov–Dec, Shishira Jan–Feb |
Watch out
- Saying Tamil Nadu gets its main rain from the south-west monsoon (it is in a rain shadow then).
- Counting 30 days after 1st June as 31st June: it is 1st July.
- Mixing up the loo (hot, dry wind) and nor’westers (evening thunderstorms).
Worked example
Suppose the monsoon bursts over Kerala on 1st June, reaches a city in central India 15 days later and a city in the north-west 34 days later. (a) On what dates? (b) How many days apart are the two cities’ onsets? (c) What is meant by a “break” in the monsoon?
Working: 1 June + 15; 1 June + 34; 34 − 15
Answer: (a) 16 June and 5 July (b) 19 days (c) a dry spell of one or more weeks during the rainy season
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