The climate of India is strongly influenced by monsoon winds. The beginning and withdrawal of the Indian Monsoon is defined in terms of zonal asymmetric temperature anomaly and withdrawal is defined in terms of vertical wind shear.
Reason for chunk of rain in Tamil Nadu
1. The Retreating southwest Monsoon Season or Northeast Monsoon season showered the peninsular India from the period of October to December. It is the only period of rainfall activity on the South peninsular India that will affects the Coastal Andhra Pradesh, Rayalaseema and Tamil Nadu-Pondicherry.
2. During the Northeast Monsoon season, weather systems like low pressure areas and cyclonic circulations move in lower latitudes of Bay of Bengal and reach the state across southwest Bay. Due to this Tamil Nadu get heavy rainfall.
3. Unlike the Southwest Monsoon, where the weather systems are spread well, the Northeast Monsoon observes a sequence of weather systems. These weather systems have a characteristic of giving rain for three to four days and thereafter taking a break for a couple of days.
4. Conditions like low pressure, depression and also accompanied by strong cyclonic wind favours the heavy rain that make the situation worse in Chennai
5. The Indian Ocean Dipole (IOD) i.e. the difference in the sea surface temperature between the two equatorial areas of the Indian Ocean – a western pole near the Arabian Sea (in western Indian Ocean) and an eastern pole closer to the Bay of Bengal (in eastern Indian Ocean) affected the wind pattern of North-east Monsoon that bring heavy rainfall in Tamil Nadu.
6. The Madden-Julian Oscillation (MJO) is one of the reasons for heavy rainfall in Tamil Nadu which have tendencies of traversing phenomenon and brings major fluctuation in tropical weather.
7. All of the above reason are climatic phenomena which are normal but the main reason of huge waterlog is just because of excessive urban planning which destroy the city’s waterways.
8. Chennai Floods is actually because of ignoring natural drains and lakes, by building over them or turning them into landfills.
9. Besides ruining its natural drains, Chennai has done nothing to build effective storm water drains. The drains are built without even considering basic factors like slopes, proximity to other water bodies or roads.
10. Rampant real estate growth cause blockage of natural water draining system that drives the city’s towards dramatic water logging.