The climatic character of India, particularly its winter season, is currently undergoing significant change due to altering patterns of Western Disturbances (WDs). These disturbances, which originate from the Mediterranean region, have been attributed as a primary cause for the uncommon winter seasons experienced in India recently. The past three years have not given way to typical winter conditions, with the country’s second-most rainy season unusually dry and hot.
Western Disturbances and Their Current Impact on India’s Winters
India’s northwest region, which traditionally receives almost 30% of its annual rainfall during winter, recorded a stark decrease in rainfall during December 2022 and February 2023. This deficit reached as high as 83% and 76% respectively in these months. Such an absence of Western Disturbances led to severe cold waves and cold days throughout much of December 2022 and January 2023. These conditions resulted from cold northern winds flowing down from the Himalayas. Additionally, Western Disturbances have also been attributed to causing hailstorms that damage crops, fog events resulting in transport disruptions, and cloud bursts leading to flash floods.
Understanding Western Disturbances
Western Disturbances are essentially a series of cyclonic storms originating in the Mediterranean region. They travel over 9,000 km to bring winter rains to northwest India. Gathering moisture from the Mediterranean Sea, Black Sea, and Caspian Sea, a Western Disturbance travels over Iran and Afghanistan before hitting the western Himalayas. Although they occur throughout the year, they predominantly reach India between December and April, owing to the winter shift of the subtropical westerly jet stream towards the rim of the Himalayas.
The Significance of Western Disturbances for India
Western Disturbances carry a major significance for India’s ecosystem. They serve as the primary source of snowfall that replenishes the winter reserves of the Himalayan glaciers, which subsequently feed major Himalayan rivers like the Ganga, Indus, and Yamuna. These low-pressure storm systems also play a vital role in aiding farmers with their rabi crop production.
Issues Accompanying Western Disturbances
Despite their importance, Western Disturbances can sometimes become agents of extreme weather events including floods, flash floods, landslides, dust storms, hail storms, and cold waves. These occurrences often lead to considerable damage to infrastructure and have a detrimental impact on life and livelihoods across affected regions.
The Influence of Climatic Phenomena on Western Disturbances
Several climatic phenomena have been linked with influencing the patterns of Western Disturbances. These include the La Nina Event, characterized by the cooling of ocean surface temperature in the Pacific Ocean; the North Atlantic Oscillation, marked by random fluctuations of air pressure over the North Atlantic Ocean; and the Subtropical Jet Stream which controls the probability of Western Disturbances impacting India and other regions at higher latitudes such as the Tibetan Plateau, or even as far up as China and Russia.
Additionally, the warming of the Arctic region has led to Western Disturbances visiting India more frequently during summers. This can increase the chances of them interacting with the southwest monsoon and other local convection systems, further escalating the risk of catastrophic weather disasters.