Northern Indian Ocean Monsoon

The word "monsoon" is known to have originated from the

Arabic word "مسوم" (mausem), which means season.

South-West Summer MonsoonThe southwestern summer monsoons occur from June throughSeptember. The Great Indian Desert (Thar Desert) and adjoining areas of the northern and central Indian subcontinent heats up too much duringthe hot seasons of summer. This causes a low pressure area over thenorthern and central Indian subcontinent. To fill up this void, themoisture-laden winds from the Indian Ocean rush in to the subcontinent.These winds, rich in moisture, are drawn towards the Himalayas, creatingwinds blowing storm clouds towards the subcontinent. However theHimalayas act like a high wall and do not allow the winds to pass intoCentral Asia, forcing them to rise. With the gain in altitude of the clouds,the temperature drops and precipitation occurs. Some areas of thesubcontinent receive up to 10,000 mm of rain.

The southwest monsoon is generally expected to begin around the start of June and dies down by September. The moisture-laden winds on reachingthe southernmost point of the Indian peninsula, due to its topography,become divided into two parts:

•  Arabian Sea Branch of the SW Monsoon•  Bay of Bengal Branch of the SW Monsoon

The Arabian Sea Branch of the SW Monsoon first hits the Western Ghats of the coastal state of Kerala, India and hence Kerala is the first state inIndia to receive rain from the South-West Monsoon. This branch of themonsoon moves northwards along the Western Ghats giving rain to thecoastal areas west of the Western Ghats. It is to be noted that the eastern parts of the Western Ghats do not receive much rain from this monsoonas the wind does not cross the Western Ghats.

The Bay of Bengal Branch of SW Monsoon flows over the Bay of Bengal heading towards North-Eastern India and Bengal, picking up moremoisture from the Bay of Bengal. Its hits the Eastern Himalaya andprovides a huge amount of rain to the regions of  North-East India,Bangladesh and West Bengal. Cherrapunji, situated on the southernslopes of the Eastern Himalaya in Shillong, India is one of the wettestplaces on Earth. After striking the Eastern Himalaya it turns towards theWest, travels over the Indo-Gangetic Plain, at a rate of roughly 1-2 weeksper state, pouring raining all along its way.

The monsoon accounts for 80 percent of the rainfall in the country. Indian agriculture (which accounts for 25 percent of the GDP and employs 70percent of the population) is heavily dependent on the rains, especiallycrops like cotton, rice, oilseeds and coarse grains. A delay of a few days inthe arrival of the monsoon can, and does, badly affect the economy, asevidenced in the numerous droughts in India in the 90s.

 

 The monsoon is widely welcomed and appreciated by city-dwellers as well,for it provides relief from the climax of summer in June. However,because of the lack of adequate infrastructure in place, most major citiesare often adversely affected as well. The roads, already shoddy, take abattering each year; houses and streets at the bottom of slopes andbeside rivers are waterlogged, slums are flooded, and the sewers and therare hurricane drain start to back up and pour out toxic filth rather thandrain it away. This translates into various minor casualties most of thetime; lack of city infrastructure coupled with changing climate patternsalso causes severe damage to and loss of property and life. Bangladesh and some regions of  India like in Assam and places of  West Bengal experiences heavy flood, which claims huge number of lives and huge lossof property and causes severe damage to economy, as evidenced in theMumbai floods of 2005. Also in the recent past, areas in India that used toreceive scanty rainfall throughout the year, like the Thar Desert, havesurprisingly ended up receiving floods due to the prolonged monsoonseason.

June 1 is regarded as the date of onset of the monsoon in India, which isthe average date on which the monsoon strikes Kerala over the years forwhich scientific data is available with the Indian MeteorologicalDepartment.

North-East MonsoonAround September, with the sun fast retreating south, the northern landmass of the Indian subcontinent begins to cool off rapidly. With this airpressure begins to build over northern India. The Indian Ocean and itssurrounding atmosphere still holds its heat. This causes the cold wind tosweep down from the Himalayas and Indo-Gangetic Plain towards the vastspans of the Indian Ocean south of the Deccan peninsular. This is knownas the North-East Monsoon or Retreating Monsoon.

While travelling towards the Indian Ocean, the dry cold wind picks upsome moisture from the Bay of Bengal and pours it over peninsular India.Cities like Chennai, which get less rain from the South-West Monsoon,receive rain from the Retreating Monsoon. About 50% - 60% of the rainreceived by the state of Tamil Nadu is from the North-East Monsoon.It is worth noting that North-East Monsoon is not able to bring as muchrain as the South-West Monsoon.