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?

A Western Disturbance is an additional tropical cyclone that forms in the Mediterranean and moves westward to northern Bangladesh and south-eastern Nepal. It brings sudden winter rain to the portions of the north of the Indian subcontinent. It is a westerly-driven non-monsoonal precipitation pattern. These storms typically get their moisture from the Mediterranean, Caspian, and Black Seas.

In contrast to their tropical counterparts, which have moisture conveyed in the lower atmosphere, extra tropical storms are a worldwide phenomenon, with humidity often carried in the upper atmosphere. When a storm system comes into contact with the Himalayas in the Indian subcontinent, moisture can occasionally be shed as rain. Wintertime sees an increase in the frequency and intensity of Western disturbances.

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. The influx of cold air from the Polar Regions towards an area of relatively warmer air with significant moisture is caused by a high-pressure system displayed over regions like Russia and neighbouring countries. An extratropical depression that moves eastward is formed in the sea due to this pressure change from cold to warm air, which creates ideal circumstances for cyclogenesis in the upper layer of the atmosphere.

Storm refers to low pressure when “extra-tropical storm” is used. It is outside of the tropics to be “extra-tropical.” The term “extra-tropical” has been applied to the WD since they are extra-tropical in origin. These eventually make their way onto the Indian subcontinent after progressively crossing the Middle East from Iran, Afghanistan, and Pakistan.

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

The place of origin of western disturbances active in northwest India during the winter season is the Mediterranean Sea, particularly the eastern Mediterranean region. These disturbances are part of the larger mid-latitude westerlies, a band of prevailing winds that flow from west to east across the mid-latitudes of the Northern Hemisphere.

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

In Northwest India, Western Disturbances are to blame for most of the winter and pre-monsoon rainfall. Cloudy skies, warmer nighttime temperatures, and unusual rain are frequently linked to these phenomena. Nearly 5–10% of India’s annual rainfall is thought to be a result of Western Disturbances.

In the winter, western winds in the Indian subcontinent deliver moderate to heavy rain to low-lying areas and heavy snow to mountainous regions. India is a rain-dependent nation, and while the southwest monsoon covers most of the country, it doesn’t bring much rain to some areas of northern India. During the winter season, from November to March, these areas depend on snow and rain from western disturbances.

Winter precipitation is significant for agriculture, especially for rabi crops like wheat, one of the most important crops in India. After winter, they begin to deteriorate. They travel over North India in the spring months of April and May, and in some areas of northwest India, they occasionally assist in the monsoon’s activation.

Western disturbances can occasionally bring about dense cloud cover and significant precipitation during the monsoon season. In north India, weak western disorders are linked to water shortages and crop failure. Residents, farmers, and governments can avoid many of the issues related to water scarcity by taking advantage of strong Western disturbances.

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

Since they also greatly contribute to soil erosion, western disturbances are not always a good thing. In the areas of Northern India, where rainfall is dispersed and density is very high, this frequently leads to the top layer of the earth being washed away. Similarly to this, they are to blame for extended cloud cover and warmer nighttime temperatures. Additionally, in cases of really heavy rain, severe crop damage is frequently noted, particularly when thick fog and mist prevail. Last but not least, the intense downpour causes major landslides and even avalanches in the area.

Therefore, the western disturbances play a vital role in the way they provide rain to India’s northern regions. They are extratropical storms; therefore in addition to causing rainfall in the area, they are a part of a highly particular and somewhat devastating environmental phenomenon.

The effects of these storms include how they change the local climate and affect crop growth, soil erosion, and other factors. As a result, although they are an essential component of India’s environmental system, the country is more severely affected by their harmful consequences because the country mostly experiences non-monsoonal precipitation.

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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