VARIABLE PATTERN OF WESTERN DISTURBANCES
VARIABLE PATTERN OF WESTERN DISTURBANCES I RACE IAS : Best IAS Coaching in Lucknow I Current Affairs
Mains General Studies: 3
(Phenomena related to Geographical Ecology)
- Recently, experts have expressed concern over the changing pattern of Western Disturbance as it may cause a huge reduction in the yield of Rabi crops in India this year.
- The winter season in India has not been normal for the last three years. The second wettest season after the monsoon in the country, that is, winter has been unusually dry and warm.
Western Disturbance :
- Western Disturbances are winter storms in the northern regions of the Indian subcontinent.
- Western Disturbances are cyclonic storms that form over land. These storms are mostly formed due to fluctuations in the temperature of the Mediterranean region due to the mixing of warm air from the tropical regions and cold air from the northern polar regions.
- The shape of Western Disturbance is a curved, spiral. Its lower mouth is narrow (which forms at an altitude of about 5,500 m above sea level) and the upper mouth is wide (which forms at an altitude of more than 9,000 m above sea level).
- Although storm systems form throughout the year, they mostly hit India between December and April, as the path of the subtropical westerly jet stream that drives them changes during winter and moves towards the Himalayas.For the rest of the year, this jet stream passes over the Himalayas, over the Tibetan Plateau and over China. The path of this jet stream varies according to the position of the sun.
- Western Disturbances collect moisture from the Mediterranean Sea, the Black Sea and the Caspian Sea during their journey and pass through Iran and Afghanistan before hitting the Western Himalayas. Strong Western Disturbances reach the Central and Eastern Himalayas and cause rain and snowfall in Nepal and Northeast India. Last time in 2019, these storm systems came to this country with full force. Since then his arrival has either been delayed or he has been weak.
- These low-pressure storms help farmers grow rabi crops in northwest India, bring snow to the Himalayas, and keep northern rivers flowing. They reach the country through a wind system called the subtropical westerly jet stream that circles the earth throughout the year.
- A rising Western Disturbance is preceded by warm, moist air and followed by cold, dry air.
- This Western Disturbance keeps the temperature warm in the extreme winter months like December and January and keeps the temperature from rising in February and March.
- Western Disturbances are also the first source of snowfall, leading to re-freezing of Himalayan glaciers during winter. It is from these glaciers that the major Himalayan rivers like the Ganges, the Yamuna and the Indus, as well as countless mountain springs and other rivers, get plenty of water.
- Whatever the Western Disturbance brings, it is not necessary that it is all good. They also bring hail, due to which the crops standing in the field get damaged. It is also responsible for fog, which disrupts air, rail, and road services, and cloud bursts, which cause flash floods.
Impact of variable pattern of Western Disturbance:
- According to the India Meteorological Department (IMD), December 2021 was the hottest month ever in the country. In the north-west region, 30 per cent of the annual rainfall occurs in winter. But, this time there was a deficiency of up to 83 per cent in the rainfall. After this, the January weather was normal, but breaking all the records, this year's February was the warmest since 1901. The northwest region received 76 per cent less rainfall.
- The main reason for the unusual cold in the years after 2020-21 is the changing pattern of Western Disturbance, which produces a series of cyclonic storms originating in the Mediterranean region.
- Clouds formed by Western Disturbances have a slight effect on the maximum temperature during the winter season. But, these clouds were missing this winter, so cold northerly winds blowing from the Himalayas caused severe cold waves and chilly weather for most of December and January in the northern Indian plains.
- Last year, due to weak Western Disturbance, the temperature in the country had increased in March. Due to this, 30-40 per cent wheat crop was damaged in Punjab, Haryana, Himachal Pradesh, Uttar Pradesh and Madhya Pradesh. Its consequences were very serious. Domestic wheat prices skyrocketed and the Center was forced to take several difficult decisions, from banning wheat exports to selling its wheat stocks at throwaway prices.
- For the last 3 years the world is in La Nina phase. It is related to the cooling of the sea surface in the Pacific Ocean. This causes the temperature of the warm tropical air to drop and the temperature fluctuations needed to form Western Disturbances weaken.
- Western Disturbances generally weaken during the La Nina phase of the El Nino-Southern Oscillation (ENSO). Because of this the winters become dry. Whereas, in the El Nino phase, the situation is opposite.
- Western Disturbances are also influenced by sudden fluctuations in air pressure over the North Atlantic Ocean, ie the North Atlantic Oscillation. It consists of a high pressure area over the Azores Islands in the central North Atlantic and a low pressure area over Iceland.
Causes for variable pattern of Western Disturbances:
- According to the University of Reading, UK “Western Disturbances are generally becoming weaker and therefore bring with them less rain. But, when they bring more rain, then the situation becomes very bad. During the last 8 years, the Western Disturbances in the month of December have been very weak except in 2017 and 2019.
- The main reason for this is the northward shift of the subtropical westerly jet stream in December.
- Such a change not only reduces the chances of Western Disturbances hitting India, but also increases the chances of them affecting higher latitudes up to the Tibetan Plateau or even China and Russia.
- It could indirectly affect the southwest monsoon, which accounts for 80 per cent of India's annual rainfall. Snow reflects most of the sun's rays that fall on it and prevents the ground from heating up. This phenomenon is called the albedo effect.
- If there is more snowfall on the Tibetan Plateau, it will not be as warm as it should be. These conditions will hinder the arrival of monsoon winds in June. When the subtropical westerly jet stream meets the polar jet stream during the winter season, it moves upward. Such melds are more likely because of Arctic warming, which makes the polar jet stream rippling.
- Although, the occurrence of Western Disturbances has reduced significantly during winters in India, but its occurrence has increased significantly in summers.
- The subtropical westerly jet stream is moving downward during the summer season due to warming in the Arctic region. This increases the chances of summer, monsoon and subsequent interaction of Western Disturbance with Southwest Monsoon.
- Along with this, the possibility of its interaction with local convection systems such as tropical depressions moving northwards from the Bay of Bengal or the Arabian Sea also increases. Such contact can lead to devastating weather disasters.
- Subtropical depressions caused by Western Disturbances cause heavy rains in parts of India where they normally do not go. In June 2013, a western disturbance caused floods in Uttarakhand, which killed over 6,000 people and caused US$1.1 billion in damage.
- A tropical depression associated with the Southwest Monsoon followed by a Western Disturbance brought moisture and then triggered flooding. In May 2021, the Taukte cyclone hit the coast of Gujarat. Due to the interaction of this cyclone with a Western Disturbance, heavy rains occurred in Delhi and surrounding areas. Due to this, the maximum temperature of the national capital fell by 16 degrees.
- Weather events are becoming more unpredictable in an every day warming world. However, experts say the exact impact is yet to be studied.
Source- Down to Earth
Mains Exam Question:
Explain the causes and impacts of Western Disturbance in India.