Knowledge Nugget | Monsoon in India: What you must know for UPSC exam

Why in the news?

The India Meteorological Department (IMD) Tuesday (May 13) announced the onset of the Southwest Monsoon over some areas of the Bay of Bengal and Andaman Sea at least a week before its scheduled arrival time, and said it would further advance to more parts of the country during the next three to four days.

This year’s monsoon onset over these regions is the earliest recorded in the past seven years. As per IMD’s monsoon onset schedule, the normal date for the monsoon onset over the South Andaman Sea, and Port Blair in the Andaman and Nicobar Islands is May 21.

Key Takeaways :

There are two notable types of monsoon in India:

(1) Southwest monsoon: It occurs from June to September. It hits Kerala on the southwestern coast and then proceeds across the country.

• This monsoon is the primary monsoon affecting India — it not only brings respite from the heat but also contributes to the country’s ecosystem and economy, especially the growing of kharif crops.

• Over 70 per cent of the country receives the majority of its annual rainfall during the June to September season. The country’s Long Period Average is 880 mm.

(2) Northeast monsoon: It is another significant and persistent aspect of the Indian subcontinent’s climate system. Its name comes from the direction of the monsoon winds, which blow from northeast to southwest.

• It occurs from October to December and affects peninsular India. It is not as intense as the southwest monsoon but is crucial for the growth of rabi crops.

• The northeast monsoon is key for Tamil Nadu, Kerala, Puducherry, Karaikal, coastal Andhra Pradesh, Rayalaseema and Yanam in southern India. Of the total annual rainfall, Tamil Nadu receives nearly 48 per cent (443.3mm) during the October to December months, important for rabi cultivation.

• The Northeast monsoon is also known as the winter monsoon, retreating monsoon, or reverse monsoon.

What is meant by below-normal, normal, and above-normal rainfall? 

1. If ‘m’ is the mean and ‘d’ is the standard deviation of any climate variable like rainfall. Assuming the time series is normally distributed, 68 per cent of the observations fall within +/- standard deviation (d) from the mean.

2. If the realised value of the variable falls between:

(i) m-d to m+d (Normal rainfall)

(ii) less than m-d (Below normal rainfall)

(iii) more than m+d (Above normal rainfall)

Effects of climate change on rain pattern in India

The study, ‘Decoding India’s Changing Monsoon Patterns: A Tehsil-level Assessment’, was carried out by Shravan Prabhu and Vishwas Chitale of the Council on Energy, Environment and Water (CEEW), a research and policy think-tank. The study found that monsoon patterns in India have been fast-shifting. It is mainly driven by the accelerating rate of climate change.

Findings of the Assessment are:

1. There has been a notable increase in rainfall in the tehsils of traditionally drier areas, like Rajasthan, Gujarat, the Konkan region, central Maharashtra, and parts of Tamil Nadu. These regions witnessed a jump of more than 30% in the southwest monsoon rainfall when compared to the baseline of 1981–2011.

2. Meanwhile, traditionally high monsoon rainfall areas such as Assam and Meghalaya saw a reduction in rainfall.

3. The southwest monsoon rainfall rose in 55% of India’s tehsils. The increase, however, has resulted from short-duration, severe rainfall, which frequently causes flash floods.

4. During the southwest monsoon in India, wet extremes account for an increasing share of total seasonal rainfall.

5. Changes in monsoon patterns can affect agriculture output and ecosystems.

6. Rainfall is not distributed evenly throughout the seasons and months.

7. The retreating monsoon rainfall spiked by more than 10% in approximately 80% of tehsils in Tamil Nadu, 44% in Telangana, and 39% in Andhra Pradesh.

BEYOND THE NUGGET: IMD’s colour-coded weather alerts and Mission Mausam

India Meteorological Department (IMD) issues colour-coded weather alerts from time to time during the monsoon. These keep citizens informed and help in greater preparedness in times of unpredictable weather conditions. Alerts by the IMD are colour-coded from Green to Red.

1. ‘Green’ stands for ‘No warning’: no action needs to be taken by the authorities, and the forecast is of light to moderate rain. According to the weather department, 15.6 mm to 64.4 mm rain is considered “moderate”.

2.‘Yellow’ alert signifies “Watch”, and authorities are advised to “Be updated” on the situation. According to the weather department, 64.5 mm to 115.5 mm rain is considered “heavy”.

3. ‘Orange’ warning stands for “Alert”, and authorities are expected to “Be prepared”. The forecast during an Orange warning is of heavy to very heavy rainfall. According to IMD, 115.6 mm to 204.4 mm rain is considered “very heavy”.

4.  ‘Red’ alert stands for “Warning”, and asks authorities to “Take action”. The forecast is for extremely heavy rainfall. The IMD, however, clarifies that “Red colour warning does not mean ‘Red Alert’,” and that it only means “take action”. According to IMD, more than 204.5 mm rain is considered “extremely heavy”.

Mission Mausam

1. Prime Minister Narendra Modi launched “Mission Mausam”, which aims to make the country a “weather-ready” and “climate-smart” nation, in Delhi on 14th January as part of the events marking the 150th foundation day of the IMD.

2. In September 2024, the Union Cabinet approved “Mission Mausam”, with a budget of Rs. 2000 crores, to enhance India’s ability to predict and respond to extreme weather events and the impacts of climate change.

3. It will be primarily implemented by three key institutions under the Ministry of Earth Sciences (MoES): the India Meteorological Department, the Indian Institute of Tropical Meteorology, and the National Centre for Medium-Range Weather Forecasting.

4. Critical elements of “Mission Mausam” include- the deployment of next-generation radars and satellite systems with advanced sensors, high-performance supercomputers, the development of enhanced Earth system models, and a GIS-based automated decision support system for real-time data sharing.

Post Read Questions

(1) With reference to the Monsoons in India, consider the following statements:

1. The southwest monsoon brings more than half of India’s annual rainfall.

2. The ‘above normal’ rainfall is attributed mainly to the El Nino conditions.

3. During the northeast monsoon, the direction of the monsoon winds is from southwest to northeast.

How many of the statements given above are correct?

(a) Only one

(b) Only two

(c) All three

(d) None

(2) With reference to the Northeast monsoon, consider the following statements:

(Sources: How India’s monsoon rain pattern has been changing amid climate change by Alind Chauhan,  IMD declares monsoon onset over South Bay of Bengal, South Andaman Sea)

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