Why in news?

The India Meteorological Department (IMD) said the southwest monsoon has reached Karnataka.

Highlights

• There will be an increase in rainfall in the coastal districts of Karnataka and Western Ghat areas.
• Westerlies will be dominant over the state

Southwest Monsoon season

• The period June to September is referred to as the ‘Southwest Monsoon’ period. Southwest Monsoon period is the principal rainy season for the Indian subcontinent. This is the summer monsoon period where the southwest monsoon holds away over the country.  The whole country receives nearly 75% of its rainfall during this period.
• Southwest monsoon sets in over the extreme south-western tip of the peninsula by the end of May. The onset of Monsoon is characterized by a sudden spurt of rainfall activity. It progresses inland in stages and covers the entire country by the middle of July.
• It starts retrieving from the extreme northwest by the beginning of September, progressively receding southwards.

Five special conditions

• The Earth System Science Organisation (ESSO) and the India Meteorological Department (IMD) take into account five conditions while making forecasts about the monsoon in April every year.

These special conditions are as follows:

1) The Sea Surface Temperature (SST) gradient between the north Atlantic and the north Pacific (conditions during December of the previous year and January of present year)

2) SST of the equatorial south Indian Ocean (conditions during February and March of the present year)

3) Mean Sea Level pressure in East Asia (conditions during February and March of the present year)

4) The surface air temperature over northwest Europe (conditions during January of the present year)

5) The warm water volume of the equatorial Pacific Ocean (conditions during February and March of the present year)

Importance of south west monsoon

• The southwest monsoon is so powerful that its performance from June to September decides the state of agricultural productivity in India, which in turn, decides the state of the economy.

• The monsoon affects a region comprising nearly 25 countries and its influence stretches across a distance of 18,000 kilometres (from east to west) and 6,000 kilometres (from south to north).