How India’s monsoon rain pattern has been changing amid climate change

The study also found that monsoon patterns in India have been fast-shifting and erratic in the past decade. This has been mainly driven by the accelerating rate of climate change. Here are five key takeaways from the analysis.

But first, a look at notable types of monsoon in India

There are two notable types of monsoon in India. First is the southwest monsoon, which occurs from June to September. It hits Kerala on the southwestern coast around June, and then proceeds across the country. The southwest 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.

The second type is the northeast monsoon, also known as the retreating monsoon, which occurs from October to December and affects peninsular India. It isn’t as intense as the southwest monsoon but is crucial for the growth of rabi crops.

THE FINDINGS

1. Rainfall increases in some of the traditionally drier regions and decreases in some of the high monsoon rainfall areas

The study found 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. In the past decade, these regions witnessed a jump of more than 30% in the southwest monsoon rainfall when compared to the baseline of 1981–2011.

Meanwhile, traditionally high monsoon rainfall areas such as Assam and Meghalaya saw a reduction in rainfall. The study said tehsils such as Pachim Nalbari Circle, Boitamari Circle, and Barnagar Circle of Assam among others received 30% less rainfall compared to the Long Period Average (LPA).

2. Regions with heightened rainfall experience more frequent heavy rainfall events

As mentioned before, southwest monsoon rainfall increased in 55% of India’s tehsils. The spike, however, has come from short-duration, heavy rainfall, which often results in flash floods, according to the study. Moreover, nearly 64% of tehsils experienced an increase in the frequency of heavy rainfall days by 1-15 days per year in the last 10 years.

Although the study does not reveal significant trends in the intensity of wet rainfall extremes, the proportion of total seasonal rainfall attributed to wet extremes is on the rise in India during the southwest monsoon.

“This trend is of particular concern as it is related to the distribution of rainfall within a season. This could be one of the reasons behind the recent occurrences of flash floods, such as in Delhi, Uttarakhand, Himachal Pradesh (in 2023), and Bangalore (in 2022),” the study added.

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

The analysis found that the southwest monsoon rainfall has decreased only in 11% of tehsils in the past decade. The worrying observation, however, is that a significant number of these tehsils are located in the Indo-Gangetic plain, northeast India, and the upper Himalayan region, crucial for India’s agricultural output. Here agricultural activities in the kharif season rely heavily on southwest monsoon rainfall. A decrease in rainfall can severely hamper the output. Not only this, these regions consist of fragile ecosystems, particularly vulnerable to extreme climate events like floods and droughts.

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

Most of the tehsils with a decreased southwest monsoon rainfall witnessed a decline in rainfall during the initial monsoon months of June and July, which are crucial for sowing kharif crops.

On the other hand, 48% of tehsils in India saw an increase in October rainfall by more than 10%, possibly due to the delayed withdrawal of the southwest monsoon from the subcontinent. This can impact the sowing of rabi crops during this time, according to the study.

5. Northeast monsoon rainfall also increased in some regions

In the past 10 years, 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. Odisha, West Bengal, Maharashtra, and Goa are also seeing an increase in rainfall during this period.