Weather anomalies driven by climate change cause scanty rain, snow in post-monsoon India

There has been a lack of rainfall during the post-monsoon season and next to no winter snowfall in some of the north Indian states as a result of a lack of intense western disturbances. 

Similarly, many south Indian states also suffered from lack of rainfall due to lower spread of the northeast monsoon rains.

This can affect the yield of Rabi crops in these regions and also availability of water in the mountains in general. The lack of snowfall in the mountains could also lead to a warmer than normal pre-monsoon season, with excess rainfall that could affect the harvesting period of Rabi crops. 

Winter precipitation in north India is essential to ensure people’s food and water security. While Rabi is the major cropping season encouraged by rainfall, the glacial streams and rivulets in the Himalayas are fed by melting snow and ice later in the season. 

The only source of rainfall and snowfall in the region are extratropical storms known as western disturbances (WD), which travel from the Mediterranean region. They induce cyclonic circulations in the lower layers of the atmosphere, which cause rainfall in the plains and snowfall in the mountains. They also interact with other wind systems such as the easterlies (winds blowing from the east) to cause rainfall in central India.

The WDs have been showing a decline in intensity in the past few years due to changing climate. The trend continued in the post-monsoon and winter seasons of 2023 as well. 

From October 1, 2023 to January 2, 2024, 16 WDs have affected India — five in October, five in November and six in December — out of which only three have been intense and caused rainfall, according to data from the India Meteorological Department (IMD), analysed by Down To Earth (DTE).  

This has caused rainfall deficits in states like Uttarakhand and Himachal Pradesh. While Uttarakhand experienced 47 per cent less rains than normal from October 1 to December 27, the deficit in Himachal Pradesh was 40 per cent, according to data from IMD. 

Eight out of the 13 districts of Uttarakhand had deficient rainfall (20-59 per cent less rainfall than normal) and four of them suffered from large deficient (greater than 60 per cent deficit) rainfall. Udham Singh Nagar district had the maximum deficit of 87 per cent.  

In Himachal Pradesh, four districts had deficient rainfall and two had large deficient rainfall. Lahaul and Spiti district had the maximum deficit of 73 per cent. 

“Himachal Pradesh and Uttarakhand received deficient precipitation since western disturbances during the post-monsoon were weak in nature,” Akshay Deoras, a research scientist at the National Centre for Atmospheric Science and Department of Meteorology, University of Reading, United Kingdom, told DTE.

“The western disturbance activity witnessed a southward dip in December, causing good rainfall over central India, but either deficient or scanty rainfall over most of northern India in December,” he added.  

Towards the end of November, a moderately intense WD interacted with a lower level trough in the easterlies and chased significant rainfall in central and western Indian states of Gujarat, Maharashtra and Rajasthan. 

“The northwest rainfall reduction is consistent with the general decreasing trend in western disturbances and the precipitation drop over the region. But the El Nino also tends to produce colder winters over parts of this region,” Raghu Murtugudde, a climate scientist at the University of Maryland and Indian Institute of Technology Bombay, told DTE.

Along with the lack of precipitation in the north, many states of southern India such as Telangana and Karnataka and even in central India such as Maharashtra have experienced deficit rainfall in the post-monsoon season (October to December). 

While the deficit was 57 per  cent in Telangana, it was 38 per cent in Maharashtra and 36 per cent in Karnataka. Bellary in Karnataka experienced 87 per cent less rains than normal which was the highest and the sub-urban district in Maharashtra suffered from the maximum deficit rainfall of 81 per cent.

In Telangana, 26 out of the 33 districts experienced large deficient rainfall, out of which Jagtial district fared the worst with 94 per cent less rains than normal. 

“Telangana and northern parts of Karnataka generally do not receive that much benefit from the northeast monsoon compared to other southern parts of the country,” said Deoras. 

“The northeast monsoon winds ere pulled more strongly over the eastern coast so Kerala and Tamil Nadu got a lot of rain but the rest of the northeast monsoon remained relatively dry”, said Murtugudde.

For other regions that get rainfall during the North East monsoon season  the El Nino pattern of decent rainfall holds true. 

“So for other regions, the overall performance of the northeast monsoon appears to be satisfactory and in line with the El Nino pattern. The performance in the initial part of the season (i.e., October) was poor due to a delay in the start of the season, but the overall rainfall deficit reduced with time, particularly following good rainfall during December”, said Deoras.  

"This pattern of rainfall is somewhat consistent with El Nino but I am still puzzled by the unusual pattern of the El Nino SST anomalies. Very warm in the usual eastern-central Pacific but the Maritime Continent never really cooled down,” said Murtugudde. 

Maritime Continent refers to the area encompassing the Indian and Pacific Oceans, which includes the archipelagos of Indonesia, Borneo, New Guinea, the Philippine Islands, the Malay Peninsula, and the adjacent seas.

Murtugudde also pointed out other weather-related anomalies that have occurred recently along with the background warming that is ongoing. 

“Eastern Indian Ocean did cool and looked like an Indian Ocean Dipole but now it’s gone. The superposition of global warming and El Nino is stronger this year because of the overall warming — the 2022 underwater volcano pumped a lot of moisture and the wildfires probably added enough additional greenhouse gases (which would further increase warming). Quite a complicated year and one can only wait to see what the new year brings,” he explained.  

Murtugudde predicted that the pre-monsoon season will be warmer and probably get more rainfall because of the Arabian Sea warming. “If the summer transitions to a La Niña then we should have excess rainfall during the monsoon season,” he concluded.

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