Climate, Monsoon and Soil Types of India
India has a tropical monsoon type of climate, which means that the year is divided into a hot, a wet and a cool season and that the rains come from the monsoon winds. The climate is controlled by latitude, altitude, distance from the sea, relief and ocean currents. Because the country is so large, the climate is not the same everywhere: the Thar desert is dry while Meghalaya is one of the wettest places on earth, and the Himalayas are cold while the Deccan is warm. This variety also produces many kinds of soil, and the monsoon and the soil together decide what is grown where - a fact that examiners test again and again.
The monsoon mechanism
The main reason for the monsoon is the differential heating of land and sea and the shifting of the Inter-Tropical Convergence Zone (ITCZ). In summer the land heats up faster than the sea, low pressure forms over the northern plains, and the moist south-west winds from the Indian Ocean are drawn in. The south-west monsoon reaches Kerala around 1 June and Assam in the first week of June, and it then spreads over the whole country. The monsoon has two branches - the Arabian Sea branch and the Bay of Bengal branch - and it is the Bay of Bengal branch, deflected by the hills of the North-East, that brings heavy rain to Assam and the North-East.
The seasons and the retreating monsoon
The year is divided into four seasons: the winter, the summer or hot weather season, the south-west monsoon or rainy season and the retreating monsoon or autumn. After the rains withdraw, the weather in October turns hot and humid, and this is called the October heat. The retreating monsoon and the north-east monsoon then bring rain to the eastern coast, especially Tamil Nadu, which gets most of its rain in this season while the rest of the country is drying out.
El Nino, La Nina and western disturbances
El Nino is the warming of the eastern Pacific Ocean waters, and it generally weakens the Indian monsoon, while La Nina is the cooling of those waters and usually brings a good monsoon. In winter, the western disturbances - winds coming from the Mediterranean region - bring rain and snow to the north-western plains of Punjab, Haryana and western Uttar Pradesh. In spring, thunderstorms called norwesters or Kalbaisakhi bring sudden rain and hail; in Assam this storm is locally called Bordoisila.
Rainfall distribution
The heaviest rainfall in India is recorded at Mawsynram in Meghalaya, with an average of about 11,000 millimetres, and Meghalaya is the state with the highest rainfall. Assam receives about 2,000 to 3,000 millimetres, which makes it a wet state. The lowest rainfall is found in Jaisalmer in Rajasthan and around Leh, and Rajasthan is the driest state of India. This uneven distribution is why irrigation is so important in the west and why floods are a yearly problem in the east and the North-East.
Soils of India
The alluvial soil is the most widespread soil of India. It is divided into the newer khadar, deposited by rivers on floodplains, and the older bangar, found at a higher level; the new alluvial soil is the most fertile soil of the Brahmaputra valley. The black or regur soil is formed by the weathering of basaltic lava and is best for cotton; it is found mainly in the Deccan plateau of Maharashtra, Gujarat and Madhya Pradesh. The red and laterite soils occur in the hilly areas of Assam and other parts, and laterite soil is formed in areas of high rainfall and high temperature, where leaching removes the plant nutrients. The arid or desert soil covers the desert regions of Rajasthan, and tea grows best in the well-drained acidic soils of the foothill regions.
Soil erosion and conservation
In Assam the main causes of soil erosion are floods, deforestation and shifting or jhum cultivation. Across India, erosion is checked by methods such as terrace cultivation on slopes, contour ploughing, strip cropping, shelter belts of trees, check dams and the reforestation of bare hills. A useful record for exams is that Madhya Pradesh has the largest area under forest in India, while Mizoram has the highest forest cover as a percentage of its area.
Quick revision
For quick revision, remember the monsoon as a system: land and sea heating, the ITCZ, the south-west winds arriving in Kerala on 1 June and reaching Assam in the first week of June, the Bay of Bengal branch soaking the North-East, and the retreating monsoon wetting Tamil Nadu. Keep the extremes ready - Mawsynram the wettest and Jaisalmer the driest - and pair each soil with its use: alluvial for general crops, black for cotton, laterite in high rain and heat, arid in the desert and well-drained acidic soil for tea. Finally, remember that Madhya Pradesh leads in forest area and Mizoram in forest percentage, and that terrace cultivation, check dams and afforestation are the standard answers for soil conservation.
How to prepare this topic
- Learn the monsoon step by step: differential heating, the ITCZ, the south-west winds, the two branches and the arrival dates in Kerala and Assam.
- Fix the rainfall extremes: Mawsynram the highest, Jaisalmer and Leh the lowest, Meghalaya the wettest state and Rajasthan the driest.
- Pair each soil with its crop and region - black soil with cotton in the Deccan, laterite with high rain and heat, arid with the desert and acidic soil with tea.
- Keep the winter and spring weather terms apart: western disturbances for winter rain in the north-west and norwesters or Bordoisila for spring storms in Assam.
- Remember the soil conservation methods and the forest records: Madhya Pradesh for area and Mizoram for percentage.
Common exam traps
- The south-west monsoon reaches Kerala on 1 June, but Assam only in the first week of June.
- El Nino weakens the monsoon, while La Nina generally strengthens it.
- Khadar is the new and more fertile alluvial soil; bangar is the older alluvial soil.
- The retreating and north-east monsoon gives rain to the Tamil Nadu coast, not to the whole country.
- Black soil is best for cotton, not for tea; tea prefers well-drained acidic soils.
Frequently Asked Questions
What is the reason for the monsoon in India and when does it reach Kerala and Assam?
The main reason for the monsoon is the differential heating of land and sea together with the shifting of the Inter-Tropical Convergence Zone, which draws the moist south-west winds from the Indian Ocean towards the heated land. The south-west monsoon reaches Kerala around 1 June and Assam in the first week of June, after which it spreads over the whole country. The Bay of Bengal branch, deflected by the hills of the North-East, brings heavy rainfall to Assam and the North-East.
Which places in India receive the highest and the lowest rainfall?
The highest rainfall in India is recorded at Mawsynram in Meghalaya, with an average of about 11,000 millimetres, and Meghalaya is the state with the highest rainfall. Assam receives about 2,000 to 3,000 millimetres. The lowest rainfall is found at Jaisalmer in Rajasthan and around Leh, and Rajasthan is the driest state of India. This uneven distribution makes irrigation vital in the west and causes floods in the east.
What are the main soil types of India and which crops suit them?
Alluvial soil is the most widespread soil of India and is divided into the newer khadar and the older bangar, with the new alluvial soil the most fertile in the Brahmaputra valley. Black or regur soil, formed from basaltic lava, is best for cotton and is found in the Deccan region of Maharashtra, Gujarat and Madhya Pradesh. Red and laterite soils occur in the hills of Assam, arid soil covers the Rajasthan desert, and well-drained acidic soils suit tea.
What are El Nino, La Nina and the western disturbances?
El Nino is the warming of the eastern Pacific Ocean waters and it generally weakens the Indian monsoon, while La Nina is the cooling of those waters and usually brings a good monsoon. The western disturbances are winds from the Mediterranean region that bring winter rain and snow to the north-western plains of Punjab, Haryana and western Uttar Pradesh. In spring, norwesters or Kalbaisakhi bring sudden storms, called Bordoisila in Assam.
What causes soil erosion in Assam and how is soil conserved in India?
In Assam the main causes of soil erosion are floods, deforestation and shifting or jhum cultivation. Across India, erosion is controlled by terrace cultivation on slopes, contour ploughing, strip cropping, shelter belts of trees, check dams and the reforestation of bare hills. For records, Madhya Pradesh has the largest area under forest in India, while Mizoram has the highest forest cover as a percentage of its area.