Cause of climate change

Chennai, Tamil Nadu, India is at 13°0’N, 80°11’E . Chennai, Tamil Nadu has a tropical wet and dry/ savanna climate with a pronounced dry season in the high-sun months, no cold season, wet season is in the low-sun months. According to the Holdridge life zones system of bioclimatic classification Chennai, Tamil Nadu is situated in or near the tropical dry forest biome the mean annual temperature is 28.8 degrees Celsius (83.8 degrees Fahrenheit Average monthly temperatures vary by 8.3 °C (14.9°F). This indicates that the continentality type is hyperoceanic, subtype barely hyperoceanic.

On average there are 2716 hours of sunshine per year. Visit the sunshine and daylight section to check monthly details including how high in the sky the sun reaches each month.

South-west Monsoon/Summer Monsoon (June, July, August and September)

The SW monsoon is the most significant feature of the Indian climate. The season is spread over four months, but the actual period at a particular place depends on onset and withdrawal dates. It varies from less than 75 days over West Rajasthan, to more than 120 days over the south-western regions of the country contributing to about 75% of the annual rainfall. The onset of the SW monsoon normally starts over the Kerala coast, the southern tip of the country by 1st June, advances along the Konkan coast in early June and covers the whole country by middle of July. However, onset occurs about a week earlier over islands in the Bay of Bengal. The monsoon is a special phenomenon exhibiting regularity in onset and distribution within the country, but inter-annual and intrannual variations are observed. The monsoon is influenced by global and local phenomenon like El Nino, northern hemispheric temperatures, sea surface temperatures, snow cover etc. The monsoonal rainfall oscillates between active spells associated with widespread rains over most parts of the country and breaks with little rainfall activity over the plains and heavy rains across the foothills of the Himalayas. Heavy rainfall in the mountainous catchments under ‘break’conditions results flooding over the plains. However, very uncomfortable weather due to high humidity and temperatures is the feature associated with the Breaks. Cyclonic systems of low pressure called ‘monsoon depressions’ are formed in the Bay of Bengal during this season. These systems generally form in the northern part of the Bay with an average frequency of about two to three per month and move in a northward or north-westward direction, bringing well-distributed rainfall over the central and northern parts of the country. The distribution of rainfall over northern and central India depends on the path followed by these depressions. SW monsoon current becomes feeble and generally starts withdrawing from Rajasthan by 1st September and from north-western parts of India by 15th September. It withdraws from almost all parts of the country by 15th October and is replaced by a northerly continental airflow called North-East Monsoon. The retreating monsoon winds cause occasional showers along the east coast of Tamil Nadu, but rainfall decreases away from coastal regions.

Post-monsoon or Northeast monsoon or Retreating SW Monsoon season (October, November and December)

North-East (NE) monsoon or Post-monsoon season is transition season associated with the establishment of the north-easterly wind regime over the Indian subcontinent. Meteorological subdivisions namely Coastal Andhra Pradesh Rayalaseema, Tamil Nadu, Kerala and South Interior Karnataka receive good amount of rainfall accounting for about 35% of their annual total in these months.Many parts of Tamil Nadu and some parts of Andhra Pradesh and Karnataka receive rainfall during this season due to the storms forming in the Bay of Bengal. Large scale losses to life and property occur due to heavy rainfall, strong winds and storm surge in the coastal regions. The day temperatures start falling sharply all over the country. The mean temperatures over north-western parts of the country show decline from about 38°C in October to 28°C in November. Decrease in humidity levels and clear skies over most parts of north and central India after mid-October are characteristics features of this season (NATCOM 2004, IMD 2010)


The el niño weather phenomenon, which can cause global famines, floods and even wars, has a 90 per cent chance of striking this year, according to the latest forecast released to the Guardian.

El Niño begins as a giant pool of warm water swelling in the eastern tropical Pacific that sets off a chain reaction of weather events around the world, some devastating and some beneficial.

India is expected to be the first to suffer, with weaker monsoon rains, followed by further scorching droughts in Australia and collapsing fisheries off South America. But some regions could benefit, in particular the U.S., where El Niño is seen as the “great wet hope”, bringing rains that could break the searing drought in the west.

The latest prediction is from the European Centre for Medium-range Weather Forecasts, which is considered one the most reliable of the 15 or so prediction centres around the world. “It is very much odds-on for an event,” said Tim Stockdale, principal scientist at the centre, who said 90 per cent of their scenarios deliver an El Niño. “The amount of warm water in the Pacific is now significant, perhaps the biggest since the 1997-98 event.” That El Niño was the biggest in a century, producing the hottest year on record at the time and major global impacts, including a mass die-off of corals.