Madhavi Gaur
July 25, 2023 09:44
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A Western Disturbance is an additional type of cyclone that originates in the Mediterranean and moves westward, reaching as far as northern Bangladesh and southeastern Nepal. It brings abrupt winter rainfall to the northern regions of the Indian subcontinent. In this article we will learn about the Western Disturbances in India and its effects on the Climate of India.
These cyclones are driven by westerly winds and occur outside the monsoon season. Unlike tropical cyclones, which draw moisture from the lower atmosphere, extra-tropical storms are a global phenomenon, and their moisture often comes from the upper atmosphere. These storms derive their moisture from sources like the Mediterranean Sea, the Caspian Sea, and the Black Sea.
When these storm systems encounter the Himalayas in the Indian subcontinent, some of the moisture can occasionally be released as rain. During wintertime, there is an increase in the frequency and intensity of Western disturbances.
Western Disturbances, also known as Extra-Tropical Cyclones or Mid-Latitude Cyclones, are low-pressure systems that originate in the Mediterranean region and move eastwards across central Asia. As they traverse, they bring significant changes to the weather in India, particularly in the northern and northwestern regions. These disturbances typically occur during the winter months, from November to April, with their frequency peaking in January and February.
Western Disturbances exhibit several distinct characteristics that set them apart from other weather systems:
Western Disturbances in India have a profound impact on India’s weather patterns and climate:
Weather agencies and meteorological departments closely monitor Western Disturbances to provide accurate forecasts. Advanced weather models and satellite data help in predicting the movement, intensity, and impact of these systems. Timely warnings enable authorities to take precautionary measures and mitigate any adverse effects.
Western Disturbances, also known as extratropical cyclones or mid-latitude cyclones, are weather systems that originate in the Mediterranean region and move eastwards towards the Indian subcontinent. These disturbances are responsible for bringing winter rains and snowfall to various parts of India, especially in the northern and northwestern regions.
The Map below depicts the Western Disturbances in India:
When Western Disturbances interact with the Himalayan mountain range, they often cause precipitation in the form of rain or snow. The amount of rainfall or snowfall varies depending on the intensity of the disturbance and the time of the year. These weather systems play a crucial role in replenishing water resources, especially for agriculture, in parts of Northern India.
The Map below depicts the Western Disturbances in India:
The weather phenomenon called Western Disturbance originates in the Mediterranean Sea. It occurs when cold air from the Polar Regions moves towards an area with relatively warmer air, containing significant moisture. This movement is caused by a high-pressure system typically observed over regions like Russia and neighboring countries. As the cold air meets the warm air, a change in pressure occurs, leading to the formation of an extratropical depression over the sea. This pressure shift from cold to warm air creates favorable conditions for cyclogenesis in the upper atmosphere.
When we use the term “extratropical storm,” it refers to a low-pressure system that is outside the tropical regions. Western Disturbances are classified as extratropical since they originate outside the tropics. After forming in the Mediterranean Sea, these disturbances progress eastward, eventually crossing the Middle East through Iran, Afghanistan, and Pakistan before reaching the Indian subcontinent.
In 2021, Delhi experienced unusually heavy rainfall during October due to western disturbances, making it the wettest October in 65 years. The Safdarjung weather observatory recorded 122.5 mm of rainfall, significantly higher than the average 28 mm.
Furthermore, January and February of the same year received above-average precipitation. However, November 2021 and March 2022 remained dry, and an early onset of summer occurred, with heat waves starting at the end of March 2022. In February 2022, the maximum temperature was kept relatively low due to several western disturbances that brought cloud cover.
During March 2022, the northwest region of India did not experience active western disturbances. The absence of cloud cover and rain resulted in high temperatures remaining prevalent.
Western disturbances, while playing a crucial role in providing rain to India’s northern regions, also bring about several undesirable effects. Their contribution to soil erosion is a significant concern, particularly in densely populated areas with dispersed rainfall patterns, where the top layer of the earth is frequently washed away. Additionally, these disturbances are responsible for extended cloud cover and higher nighttime temperatures. During heavy rainfall, they can cause severe crop damage, especially when accompanied by thick fog and mist. Moreover, the intense downpour often triggers major landslides and even avalanches in the region.
Despite being an essential component of India’s environmental system as extratropical storms, they are associated with a unique and somewhat devastating phenomenon. These storms profoundly influence the local climate and impact crop growth, soil erosion, and other factors. Due to India’s reliance on non-monsoonal precipitation, the country is more susceptible to the adverse consequences of these disturbances, making them a mixed blessing with both beneficial and harmful effects.
The western disturbances significantly impact the winter weather in regions up to Patna (Bihar), occasionally resulting in beneficial rainfall for the existing rabi crops like wheat, barley, mustard, gram, and lentils.
During winter in the Indian Subcontinent, the mountains experience considerable snowfall, while low-lying areas receive moderate to heavy rain primarily due to western disturbances. These disturbances play a major role in bringing post-monsoon and winter precipitation, especially in northwest India. Precipitation during the winter months is crucial for the success of rabi crops.
The agricultural sector in northwestern India heavily relies on the winter rainfall brought by Western Disturbances. Farmers plan their Rabi crop cultivation based on the expected precipitation. Additionally, the snowfall in the Himalayas ensures a steady flow of water in rivers, supporting irrigation and hydropower generation during the dry seasons.
Wheat, being one of the most important crops, plays a significant role in India’s food security. Typically, four to five western disturbances occur during the winter, each bringing variations in rainfall distribution and volume. Key indicators of Western Disturbances include cloudy skies, warmer nighttime temperatures, and unexpected rain.
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