Why does pre-monsoon rainfall occur? How to differentiate it from monsoon rains

As the country battles with extreme heatwave, all eyes are on the upcoming monsoon season which typically starts in June. Indian monsoon lasts from June to September, with large areas of western and central India receiving more than 90% of their total annual precipitation during the period while southern and northwestern India receives 50%-75% of their total annual rainfall.

Monsoon reaches Kerala on June 1. However, pre-monsoon rains have already started in some parts of the country which is providing some relief to people from scorching summer heat. So here we try to understand what is pre-monsoon rain and how is it different from the monsoon season. 

The term Mango showers is used to describe the occurrence of pre-monsoon rainfall.

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Why does pre-monsoon rainfall occur?

As the sun shifts northward towards the Tropic of Cancer after the Vernal Equinox, the whole India experiences an increase in temperature and marks the commencement of pre-monsoon season. As per the India Meteorological Department, pre-monsoon is from March to May. Any rainfall in this period can be attributed as pre-monsoon showers. 

Pre-Monsoon rain commences and withdraws from Peninsular India earlier than the northern parts. June is very much a pre-monsoon season for north India but the Southwest Monsoon generally strikes Kerala by June 1. Simultaneously, monsoon reaches parts of northeast India.

Pre-monsoon season is synonymous with heat and humidity with uncomfortable conditions throughout the day and night. However, fairly stronger winds bring down temperatures to a comfortable level during monsoon season.

Clouds are more of vertical in nature during the pre-monsoon season and mostly come up during late afternoon and early evening hours. They are triggered by high temperatures and towering clouds build up.

It is also called Kalbaisakhi in West Bengal, Mango Showers in Karnataka and Blossom Shower in Kerala. Generally it is called April Rains. They help in the early ripening of mangoes and often referred to as 'mango showers'. 

The classic features of these showers are the form of precipitation which is mainly convective. Daytime heating triggers the convection process and hence you get the thunderstorms after the post-noon period. So, ideally a day will begin with a clear sky and summer like temperature but from the afternoon, these pre-monsoon showers start occurring and cool winds will decrease the temperatures.

What is monsoon rain?

A monsoon is a seasonal change in the direction of the prevailing or strongest winds of a region. Monsoons cause wet and dry seasons throughout much of the tropics. Monsoons are most often associated with the Indian Ocean. Monsoons always blow from cold to warm regions.

The monsoon season in India is made up of many large and elaborate processes. In the month of May-June, the Indian peninsula starts heating up with heat, while the temperature in and around the Arabian Sea and Bay of Bengal is comparatively low.

Due to this temperature difference, clouds of water from the sea move in large quantities towards north India and while going there, it rains all over India, which is called monsoon rain.

Features of pre-monsoon and monsoon rains

Pre-monsoon rains are characterised by the conditions of heat and humidity. This uncomfortable condition lasts all day and night. But strong winds give some relief from the heat. But in monsoon, due to winds and prolonged rains, there is a drop in temperature. Apart from this, there is also a big difference between clouds and their flow. The pre-monsoon clouds move upwards and usually rain in the evening.

Pre-monsoon clouds move upwards and form at higher temperatures. On the other hand, monsoon clouds are layered clouds that travel long distances from one place to another. These layers have high moisture content. The pre-monsoon rains are strong and pungent, which ends in a day or two. At the same time, the shift of monsoon rain is long and this rain also happens again and again.

Monsoon rains can come at any time of the day. But pre-monsoon rains come only in the afternoon or in the evening. Apart from this, there is also a difference of wind in both the rains. Pre-monsoon rains are dust storms caused by gusty winds.

Due to the greater difference in heat and temperature, the sea and land breeze show more emphasis before the onset of monsoon, this creates humidity and cloudy conditions. But such winds are not prominently seen in monsoon. Yes, many times strong winds of cyclone created due to monsoon are definitely seen.

Pre-monsoon rains as they are said are like local rains only in a limited area. But monsoon rains cover a very large area and during this time there is uniform weather in the entire area. Being an agricultural country, the people of India wait for the monsoon rains because the entire economy depends on food crops which depends on rains.