Thunderstorms, lightning and many such events are witnessed during Pre-monsoonal season in India. Explain their formation process and its impact on various regions of India.

Pre-monsoon season is from April to May in India. It is the precursor to the full onset of monsoon. Due to high-pressure over the Indian subcontinent, the moisture bearing winds are not attracted to the mainland.

Process of Pre-monsoon rainfalls:

• Oppressive heat is common in summer. It leads to warm air rising conventionally.
• This warm, light air ascends to considerable height in the atmosphere.
• Moreover the temperature of the air parcel reduces and its humidity capacity also falls.
• Thus clouds are formed due to condensation of water vapour in the air.
• The size of clouds increases due to accumulation of water droplets.
• When clouds become too heavy, torrential rain and lightning occur.
• Therefore cumulonimbus clouds formed by convectional heating of air, lead to rain.

In some regions, this rainfall has positive impact:

• Aids coffee cultivation in Kerala and Karnataka (Blossom showers).
• Helps the mango crop develop in Karnataka (Mango showers).

However, this has an adverse impact elsewhere, in form of natural disasters/discomfort:

• Kal Baisakh – Rains in West Bengal.
• Bardoli Chheerha – Heavy rain and rain in Assam.

Therefore the pre-monsoon and thunder storms originate due to unique reasons. They have proven a mixed blessing for India.

Topics: GS-I: Salient Features of World Physical Geography • GS-I: Important Geophysical Phenomena