During the hot season, as we move from southern to northern part of the country, the average temperature increases. Starting in April, the temperature rises and slowly the maximum day temperature exceeds 37o C in northern plains of India. By mid-May, day temperature may touch 41o C to 42 o C in many parts of the country, especially in the north-west plains and central India.
Even minimum temperature does not go below 20o C. The northern plain experiences dry and hot winds called ‘Loo’.
From the climographs above, note the approximate average temperature for May for the
four places and mark them on the above map. Towards the end of the summer season, pre-monsoon showers (‘bursting monsoon’) are common in the Deccan Plateau. These help in the early ripening of mangoes and other plantation crops in peninsular India. Hence they are locally known as mango showers in Andhra Pradesh.
Advancing monsoon:
The climate of India is strongly influenced by the monsoon winds. The sailors who came
to India during olden days noticed the regular periodic reversal of winds. They used these winds to sail towards the Indian coast. Arab traders named this seasonal reversal of wind system ‘monsoon’.
The monsoon forms in the tropical area approximately between 200 N and 200 S latitudes. The south-east trade winds from the southern hemisphere carry moisture as they flow over the Indian Ocean and towards the equatorial low pressure zones. After crossing the equator, these winds deflect west -wards towards the low pressure formed in the Indian sub-continent. The heating of land creates low pressure on the land mass of Indian sub-continent, especially over central India and the Gangetic plain. Together with this, the Tibetan plateau gets intensely heated and causes strong vertical air currents and the formation of low pressure over the plateau at above 9 kms altitude.
They then flow as the southwest monsoon. The Indian peninsula divides them into two
branches - the Arabian Sea branch and the Bay of Bengal branch. The Arabian Sea branch
arrives at the west coast of India and moves north ward. The Bay of Bengal branch strikes the Bengal coast and the southern face of the Shillong plateau.
Then it gets deflected and flows westward along the Gangetic valley. Both the branches
reach India by the beginning of June, which is known as “onset of monsoon”. They gradually spread over the entire country in four to five weeks. The bulk of the annual rainfall in India is received from south-west monsoon. The amount of rainfall is very high along the west coast due to the Western ghats, and in north-east India due to the high peaked hills. Tamil Nadu coast (Coramandel), however, remains mostly dry during this season as it falls in the rain shadow area of the Arabian Sea branch and is parallel to the Bay of Bengal branch.
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