Western Disturbances in India, Origin, Impact, Variations

Western Disturbances in India

Another western disturbance is expected to arrive around November 25, potentially extending the thunderstorm and hailstorm activity in central India until November 26 or 27. The Indian Meteorological Department (IMD) has predicted thunderstorms and hailstorms in central India due to an approaching western disturbance. A separate western disturbance will bring light snowfall and rainfall to Jammu & Kashmir.

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What are Western Disturbances?

Western cyclonic disturbances are winter weather events caused by westerly winds from the Mediterranean region. The term “Western” indicates the direction from which these disturbances originate in relation to India. They are called “disturbances” because the air within these low-pressure systems is often unstable. These extratropical storms bring winter rain to the northwestern parts of the Indian subcontinent. They gradually move across the Middle East, traveling from Iran, Afghanistan, and Pakistan before entering India. These storms typically get their moisture from the Mediterranean, Caspian, and Black Seas.

Characteristics of the Western Disturbances

• They are generally related to cloudy skies, higher night temperatures unusual rain, and Excessive precipitation which causes crop damage, landslides, floods and avalanches.
• It is specifically the ones in winter, moderate to heavy rain in low-lying areas and heavy snow in mountainous areas of the Indian Subcontinent.

Origin of Western Disturbances

The extratropical storm known as Western Disturbance originates in the Mediterranean Sea. Cold air from the Polar Regions moves towards warmer, moist areas because of high pressure over places like Russia. This creates a low-pressure system in the sea, which moves east and can lead to the formation of storms in the upper atmosphere.

An “extra-tropical storm” means a storm with low pressure that forms outside the tropics. These storms, called Western Disturbances (WD), start outside the tropics and travel across the Middle East from Iran, Afghanistan, and Pakistan before reaching the Indian subcontinent.

Place of origin of Western Disturbances Active in North Western India in Winter Season

Origin:

• In winter, high pressure around Ukraine pushes cold polar air towards warmer, moist air in lower latitudes.
• The warm air, part of the westerlies, carries a lot of moisture.
• When these air masses meet, they form a front.

Eastward Movement Towards India:

• This front causes clouds and heavy rain, leading to temperate cyclones in the upper atmosphere.
• These cyclones meet the subtropical westerly jet stream, which moves them eastwards.
• As they travel, they gather moisture from the Caspian Sea and Persian Gulf.
• They enter India mainly through Jammu & Kashmir, Punjab, Haryana, and Rajasthan.

Western disturbances originate from the Mediterranean Sea due to a combination of factors:

• Temperature contrast: The warm Mediterranean Sea provides a source of moisture and energy for these disturbances.
• Upper-level jet streams: Strong upper-level jet streams, which are narrow bands of strong winds, guide these disturbances eastward.
• Cyclonic activity: Cyclogenesis, the process of cyclone formation, occurs frequently in the eastern Mediterranean region, providing the impetus for western disturbances to develop.

Western Cyclonic Disturbances

Western Cyclonic disturbances are low-pressure systems that originate over the Mediterranean Sea. Under the influence of subtropical westerly jet streams, these wind systems reach India and cause rainfall.

Impact of Western Disturbances

Indian Climate:

• Western Disturbances bring rain, snow, and fog to northern India and Pakistan.
• They carry moisture from the Mediterranean Sea and the Atlantic Ocean.
• These disturbances are crucial for winter and pre-monsoon rain, aiding the Rabi crop in northern India.
• Sometimes, they cause extreme weather like floods, landslides, dust storms, hailstorms, and cold waves, which can be harmful.
• In April and May, they help activate the monsoon in parts of northwest India.
• During the monsoon, they can cause heavy rain and dense clouds.
• Weak disturbances can lead to crop failure and water issues, while strong ones help manage water scarcity.

Agriculture:

• 4-5 Western Disturbances form each winter, with varying rainfall.
• Winter rain is vital for Rabi crops like wheat, impacting states like Haryana and Punjab.
• Weak disturbances can cause crop failure, while strong ones help with water scarcity.

Potential Risk of Disaster:

• Unseasonable rain and hail can damage crops in states like Haryana, Punjab, Madhya Pradesh, and Rajasthan.
• They can also cause lightning, leading to casualties.
• Disasters like the Leh cloudburst (2010), Kashmir floods (2014), and Uttarakhand floods (2013) were due to Western Disturbances, causing significant destruction and loss of life.

Western Disturbances Variations

In recent years, there has been a trend towards more frequent and intense Western Disturbances (WDs). This is likely due to various factors, including climate change, El Niño, and La Niña. The variation of WDs can have a significant impact on the climate and water resources of North India. For example, a year with weak WDs can lead to drought, while a year with solid WDs can lead to flooding. Here are some specific examples of how the variation of WDs has impacted North India in recent years:

• 2020-21, North India experienced a severe winter drought due to weak WDs. This led to a shortage of drinking and irrigation water and impacted agricultural production.
• In 2021-22, North India experienced a series of solid WDs, which led to heavy rainfall and snowfall. This caused flooding and landslides in some areas and disrupted transportation and flights.

The variability of WDs is a complex issue, and we still need to learn much. However, by understanding the factors that influence WDs and developing better forecasting models, we can better prepare for and manage the associated risks.

Effects of Western Disturbances in India

Western disturbances can cause soil erosion in Northern India because they bring heavy, scattered rain that washes away the top layer of soil. They also lead to long periods of cloud cover and warmer nights. Heavy rain from these disturbances can damage crops, especially when there is thick fog and mist. They can also cause landslides and avalanches.

While western disturbances are important for bringing rain to Northern India, they are also extratropical storms that can have harmful effects. They change the local climate, affect crop growth, and cause soil erosion. Although they are a key part of India’s weather system, their negative impacts are significant because they bring non-monsoon rain.

Western Disturbances Importance

The western disturbances influence the winter weather up to Patna (Bihar) and occasionally produce rainfall that is very good for the existing rabi crops (wheat, barley, mustard, gram, lentil, etc.).

The Indian Subcontinent has considerable snowfall in the mountains and moderate to heavy rain in low-lying areas due to western disturbances, particularly in the winter. In northwest India, they are to blame for the majority of the post-monsoon and winter precipitation. In agriculture, precipitation during the winter months is crucial, especially for rabi crops.

One of the most significant crops among them, wheat contributes to India’s ability to meet its food security needs. During the winter, four to five western disturbances typically occur. Every western disturbance causes a different variation in rainfall distribution and volume. Cloudy skies, warmer nighttime temperatures, and unexpected rain typically indicate Western Disturbances.

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