When north and south winds collide, torrential rain falls in south-east Asia

The monsoon season is crucial for agriculture, making up 80% of annual rainfall, but also extremely destructive

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anuary brings torrential rain to south-east Asia – more than 250mm fell in just two days in Singapore last year. This is because of the monsoon, a pattern of wind and rainfall, the name of which stems from the Arabic word for “season”.

The monsoon is sometimes described in terms of a sea breeze, in which the wind reverses direction in the morning and evening as the relative temperature of land and sea change, blowing out to sea at first and then inland as the land cools.

Meteorologists prefer to describe the monsoon in terms of the seasonal movement of the intertropical convergence zone (ITCZ), the area where north and south winds collide. Sailors knew the ITCZ as the doldrums, where no wind blew.