Climate Change

What are Western Disturbances? How do they impact rain and snowfall in India?

It is a non-monsoonal precipitation pattern that induces low pressure systems in the lower layers of the atmosphere; this, ultimately, causes rainfall in the plains and snowfall in the mountains

By DTE Staff
Published: Wednesday 10 January 2024

The only source of rainfall and snowfall in the hills of north India are extratropical storms known as western disturbances (WDs). These form in the Mediterranean region and travel eastward to northern Bangladesh and south-eastern Nepal.

It is a non-monsoonal precipitation pattern that induces low pressure systems in the lower layers of the atmosphere. This, ultimately, causes rainfall in the plains and snowfall in the mountains.

The WDs have been showing a declining trend in intensity in the past few years due to changing climate. 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 the India Meteorological Department (IMD).

Media reports say that snowfall has reduced drastically in the mountains of Jammu and Kashmir even though there has been rainfall during the post-monsoon season.

The lack of snowfall in the mountains affects the yield of Rabi crops in some regions and availability of water in the mountains in general. The majority of Rabi crops are sown there in October and November, so rains during these months are extremely important.

More than 80 per cent of Himachal Pradesh’s agricultural land is rainfed. Only four years between 2004 and 2023 saw normal or above-normal rainfall in October, according to the IMD.

Experts have attributed the continuous decrease in rainfall in the post-monsoon season for the last few years to climate change. S P Bhardwaj, a horticulturist (former joint director at Dr YS Parmar University of Horticulture and Forestry in Nauni, Solan) told Down To Earth (DTE) that the fruit trees are stressed due to the prolonged dry spell.

“Apple production will suffer greatly as a result of the prolonged drought and lack of snow. The dry spell has also caused problems for horticultural farmers who were planning to plant new orchards,” said Bhardwaj.

“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,” Akshay Deoras, a research scientist at the National Centre for Atmospheric Science and Department of Meteorology, University of Reading, United Kingdom, told DTE.

Towards the end of November, a moderately intense WD interacted with an extended low pressure area embedded within the winds blowing from the east over central India and caused significant rainfall in central and western Indian states of Gujarat, Maharashtra and Rajasthan.

States of southern India such as Telangana and Karnataka also experienced deficit rainfall in the post monsoon season (October to December). Apart from this, the El Nino phenomenon causes India’s monsoon rains to plummet as well.

El Nino is a climate pattern that describes the unusual warming of surface waters in the central and eastern equatorial Pacific Ocean. This happens every 2-7 years. The changes in the temperature of the ocean surface affect the trade winds in the atmosphere causing heightened temperatures and lack of rainfall in many regions.

India’s monsoon rainfall for the year 2023 hit a five-year low, marking the lowest since 2018 due to El Nino. In Kashmir, El Nino’s impact is evident through prolonged dry spells, milder winters, and diminished snowfall. Experts caution that the region is likely to face more frequent and extended dry periods in the future.

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