Why is it in the news ?
1.The southwest Monsoon has intensified across the state of Kerala with torrential rain, triggering destruction, waterlogging, landslides and uprooting of trees.
2.Five people have been killed in various rain related incidents in the state, including two in Thrissur who were struck by lightning on Saturday.
3. Landslips have been reported in various parts of the state. An orange alert warning of very heavy rainfall has been issued for Wayanad Kozhikode and Idukki and a yellow alert for districts from Ernakulam to Kasaragod.
4.The central water commission released its flood situation report, detailing significant rainfall and resultant severe flood conditions in various regions of the country with Kerala and Assam being the most affected.
5.The IMD has forecast continued heavy rainfall in districts such as Thrissur, Kozhikode,Idukki, Palakkad and Wayanad. So, the Monsoon has arrived on its scheduled date on the 1st June at the coastal area of Kerala.
How Monsoonal rains occur in India?
1.According to noted astronomer, Halley, the primary cause of the occurrence of Indian Monsoon is on account of the differential heating effects of the land and the sea. During the summer season, in the northern hemisphere when the sun’s rays are vertical on the tropic of cancer, the huge landmass of Asia heats up quickly and develops a strong low pressure centre near the lake Baikal (Siberia) and Peshawar (Pakistan). In comparison to the heating of the landmass of South Asia, the pressure over the adjacent Indian and Pacific oceans is very high. Thus, a sea to land pressure gradient develops. This leads to the surface airflow from the high pressure area over the oceans towards the low pressure areas of the heated landmass of South Asia. Since, the wind coming from oceans towards the land is warm and moist. They cause heavy rain when they come into contact with the Himalaya mountains. The moist laden winds ascend and then saturate, condense and precipitate. In the winter season, the high pressure area develops near Baikal lake (Siberia) and Peshawar (Pakistan) while the Indian and Pacific ocean remains relatively warm. Therefore, there is an outflow of air from the high pressure of the land to the low pressure of the ocean. This wind is cold and dry and therefore, incapable of giving precipitation unless it comes into contact with some water body like the sea or ocean.
2.But this theory is not universally accepted now. If the Monsoon had taken place on account of differential heating of land and sea, then the monsoonal rain would have started in the month of April and May itself, because these two months are very hot in North India and Pakistan. But the Monsoonal rains are likely to occur in 2024 after 15th June in Bihar, 25th June in UP, 30th June in Punjab and Haryana and 5th July in Pakistani Punjab.
3.Moreover, Monsoonal rainfall is not wholly orographic but they are an amalgamation of convectional, orographic and cyclonic rainfall.
4.The Monsoonal rains occur in India because of interplay of several factors. The intertropical convergence zone shifts northward between 20 degree N and 25 degree N latitude because of the vertical rays of the sun on the tropic of cancer. The northward shift of ITCZ causes withdrawal of the westerly jet stream from over the northern Indian plain. Since ITCZ is a zone of low pressure, it attracts inflow of winds from different directions. The maritime tropical air mass from the southern hemisphere after crossing the equator, rushes to the low pressure area in the south westerly direction. This moist laden air current is known as southwest monsoon. As long as westerly jet streams flowing on the Tibetan highlands and south of the Himalayas are active, no monsoonal rain occurs in Gangetic belt of India. Once the ITCZ is created between 20 degree to 25 degree north of the latitude and the westerly jet stream is withdrawn from the Gangetic basin, and the easterly jet stream flows over the southern part of the peninsula between 15 degree N to 20 degree N latitude, these phenomena leads to tropical depression into India. These depressions play a significant role in the distribution of Monsoon rainfall over the Indian subcontinent.
5.Thus, the southwest monsoon is a continuation of southeast trades deflected towards Indian subcontinents after crossing the equator between 40 degree E and 60 degree E longitudes.
6.To sum up, the shift in the position of the ITCZ between 20 degree to 25 degree N of latitudes supported by the withdrawal of the westerly jet stream over the Gangetic plain and the positioning of easterly jet stream along 15 degree N latitude after the withdrawal of westerly jet stream results into the arrival of monsoon in India.
7. The monsoon approaches the landmass of India in two branches - the Arabian sea branch and the Bay of Bengal branch, the Arabian sea branch is further split into three branches - western ghats branch, Mumbai branch and Saurashtra and Kutch branch.
8.The Bay of Bengal branch is split into Myanmar and Bangladesh Branch and another is Indian branch crossing into West Bengal. The Indian branch is split into a westward branch along the Gangetic plain from Bengal to Punjab while another branch moves into Brahmaputra Valley and goes further to Meghalaya to be stopped by Garo,Khasi and Jaintia hills, causing heaviest rainfall in Mawsynram and Cherrapunji in India.
9.Tamil Nadu remains dry during this season because its coast is situated parallel to the Bay of Bengal branch of South West Monsoon. Secondly , it lies in the rain shadow area of the Arabian sea branch of the South West Monsoon.
10.The Monsoon retreats from Northern India by the end of September. The retreating northeast monsoon during the month of October and November picks up moisture while crossing the Bay of Bengal and causes torrential rainfall over Tamil Nadu coast , Southern Andhra Pradesh, Southeast Karnataka and South East Kerala.
Features of Monsoonal rainfall
1.Southwest monsoon is seasonal in character. It occurs between June to September. However, the retreating southwest monsoon causes heavy rainfall on the coast of Tamil Nadu in the months of October and November.
2.Monsoonal rainfall is governed by a relief or topography. For example, the windward side of western ghats receives more than 250 cm annual rainfall while the leeward side has scanty rainfall. Similar situation obtains in the case of eastern Himalayas where heavy rainfall occurs.
3.The monsoonal rainfall starts declining with the increasing distance from the Bay of Bengal or the Arabian sea. For example, rainfalls are heavy in Kolkata and Patna when compared to Allahabad and Delhi.
4.Monsoonal rains occur a few days interspersed with rainless intervals known as breaks.
5.The southwest monsoon in the summer causes heavy rainfall leading to considerable runoff and soil erosion.
6.The spatial distribution is also uneven which ranges from 12 cm to more than 250 cm annual rainfall.
7.The monsoonal rainfall is sometimes erratic and delayed.
8.The monsoonal rainfalls sometimes end early causing damage to standing crops.
Its impact upon our economy
1.Southwest monsoon causes three fourth rains in India. It is a lifeline for the agricultural economy in India.
2.Since, 45% of our agricultural land is unirrigated, the monsoonal rainfalls help in the production of cotton, sugarcane, oil seeds, pulses in the areas of western and south India.
3.Heavy rainfall leads to soil erosion in the Gangetic Valley.
4.Variability of rainfall brings drought or floods every year in some parts of the country.
5. Since 42% of our people depend upon agriculture for their livelihood, any failure of monsoonal rainfall extremely impacts the agricultural productivity of our country. Since 18% of our GDP is constituted by agriculture and allied activities, any set back to the monsoonal rainfall causes immense damage to our economy.
6.A bad monsoon may lead our farmers to be entrapped in debt. Crops like rice, require large amounts of water and so any failure of monsoonal rainfall adversely impacts the productivity of rice, sugarcane and cotton.
7.Fishing activities in India depend upon monsoonal rainfall because of replenishing of water level in rivers and lakes.
8.Power generation is also impacted if there is a failure of monsoonal rainfall.
Conclusion
1.Monsoonal rainfall is essential for the Indian economy for providing vital hydropower, irrigation and sustenance to our agriculture.
2.Since the climate change is impacting the monsoonal rainfall, it is incumbent for India to take collective action along with other countries of the world to reduce the emission of the greenhouse gases.
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