Weather, climate and the factors that shape India's climate
Weather is the state of the air at a given time; climate is its pattern over a large area for 30 years or more. Six factors shape India's climate.
Weather and climate
A season is a spell of a few months in which similar weather lasts, such as the hot weather season.
Six factors that shape India's climate
| Factor | How it works | Example |
|---|---|---|
| Location (latitude) | Places near the Equator are hotter, and it gets cooler towards the poles. The Tropic of Cancer gives India a tropical south and a subtropical north | Andhra Pradesh is hotter than Haryana |
| Distance from the sea | The sea keeps coastal places neither very hot nor very cold: an equable climate. Places far from the sea have an extreme climate | Mumbai is equable; Delhi is extreme |
| Altitude | Height above sea level. The air gets thinner and cooler as we go up | Shimla in the hills is cool while Ludhiana in the plains is hot |
| Mountain ranges (relief) | The Himalayas (average 6,000 m) block cold Central Asian winds and make the monsoon winds shed their rain in India. The Western Ghats force heavy rain on their western slopes | Heavy rain on the Konkan and Malabar coasts |
| Direction of surface winds | In winter, winds blow from land to sea and are cold and dry. In summer, they blow from sea to land and bring rain | Dry winters and wet monsoon months |
| Upper air currents | Jet streams about 12,000 m up bring western disturbances in winter. In summer they shift north, over Central Asia, which helps the monsoon to start | Light winter rain in Punjab and Haryana |
Equable and extreme climate
Annual range of temperature = highest monthly mean temperature − lowest monthly mean temperature.
Western disturbances
- They are cyclonic disturbances (low-pressure systems with swirling winds) that start near the Mediterranean Sea.
- The jet streams carry them eastwards. On the way they pick up moisture, which the lesson says comes from the Persian Gulf.
- They shed it as light rain in north-west India in winter, and as snow on the higher Himalayas.
- This winter rain helps the rabi crops such as wheat.
On the map
- Tropic of Cancer (23½°N): the line dividing India into a tropical south and a subtropical north.
- Himalayas: the high wall along the north that keeps out the cold winds of Central Asia.
- Western Ghats: along the west coast; their western (windward) slopes get very heavy rain.
- Shimla and Ludhiana: a hill station and a plains city, both in north-west India, showing the effect of altitude.
- Mumbai and Chennai (coastal, equable) against Delhi and Lucknow (inland, extreme).
Families in Delhi keep both woollens and coolers, while families in Mumbai seldom need heavy woollens. That is the difference between an extreme inland climate and an equable coastal one.
3 marks: “Pick any three factors that make the climate differ across India, and show each with an Indian place.” Location: places south of the Tropic of Cancer are hotter. Distance from the sea: coasts are equable, inland places extreme. Altitude: higher places such as Shimla are cooler. Mountains: the Himalayas block cold winds and trap the monsoon. Winds and jet streams. Any three, each with an example.
2 marks: “Differentiate between weather and climate.” Weather is the state of the atmosphere over a small area at a given time and changes quickly. Climate is the sum of weather conditions over a large area for more than 30 years and is generally stable.
1 marks: “At about what height do jet streams blow over India?” About 12,000 m above sea level.
Six factors in order, L-D-A-M-W-U: Let Daddy Always Make Warm Upma (Location, Distance from sea, Altitude, Mountains, Winds, Upper air currents).