Tamil Nadu is heavily dependent on monsoon rains, and thereby is prone to droughts when the monsoons fail. The climate of the state ranges from dry sub-humid to semi-arid. The state has three distinct periods of rainfall:
- advancing monsoon period, South West monsoon from June to September, with strong southwest winds;
- North East monsoon from October to December, with dominant northeast winds;
- dry season from January to May.
The normal annual rainfall of the state is about 945 mm (37.2 in) of which 48% is through the North East monsoon, and 32% through the South West monsoon. Since the state is entirely dependent on rains for recharging its water resources, monsoon failures lead to acute water scarcity and severe drought.
Tamil Nadu is classified into seven agro-climatic zones: north-east, north-west, west, southern, high rainfall, high altitude hilly, and Cauvery Delta (the most fertile agricultural zone). The table below shows the maximum and minimum temperatures that the state experiences in the plains and hills.
|Max.||43 °C (109 °F)||32.3 °C (90.1 °F)|
|Min.||13.1 °C (55.6 °F)||3.0 °C (37.4 °F)|