Western disturbances are storms originating from the Caspian or Mediterranean Sea that bring non-monsoonal rainfall to northwest India. This is according to the India Meteorological Department (IMD), which defines a Western Disturbance as an extra-tropical storm originating in the Mediterranean. This area of low pressure can cause sudden showers, snow, and fog in northwest India. The term “disturbance” refers to an area of “disturbed” or reduced air pressure due to an equilibrium in nature where the air in a region tries to normalize its pressure.
The journey of these disturbances is from the “western” to the eastern direction, traveling eastwards on high-altitude westerly jet streams. These massive ribbons of fast winds traverse the earth from west to east, carrying the disturbances across the middle-east from Iran, Afghanistan, and Pakistan to the Indian Subcontinent.
Impact of Western Disturbances on India
The impact of a Western Disturbance (WD) is usually associated with rainfall, snowfall, and fog in northern India. Arriving with rain and snow into Pakistan and northern India, WDs carry moisture originated from the Mediterranean Sea and/or the Atlantic Ocean. These disturbances play a vital role in bringing winter and pre-monsoon rain, crucial for the development of the Rabi crop in the Northern subcontinent.
However, the effects of WDs are not always positive. At times, they can cause extreme weather events like floods, flash floods, landslides, dust storms, hail storms, and cold waves. These adverse conditions can lead to loss of life, destruction of infrastructure, and impacts on livelihoods. Interestingly, during the monsoon season, western disturbances can occasionally cause dense clouding and heavy precipitation. Besides, weak western disturbances have been associated with crop failure and water problems across north India, while strong western disturbances can help solve many issues related to water scarcity.
Recent Instances and Impact of Western Disturbances
The influence of Western Disturbances can be seen in the recent climatic variations. Excess rainfall was recorded in January and February 2022, while no rainfall was observed in November 2021 and March 2022. Interestingly, the summer began unusually early with heat waves setting in at the end of March 2022 due to a lack of WDs and cloud cover.
In contrast, multiple western disturbances led to an overcast sky, resulting in low maximum temperatures in February 2022. For instance, the lowest maximum temperature in 19 years was recorded during this time. However, active Western Disturbances evaded northwest India in March 2022, leading to persistently high temperatures due to the absence of cloud cover and rain.
It is noteworthy that the frequency of Western Disturbances has increased, but not always the precipitation associated with them, partly attributable to a warming atmosphere due to global warming. In 2021, Western Disturbances brought rain to Delhi in the first week of December. Yet, colder weather is expected in the city as the maximum temperature is likely to fall to around 24 degrees by December 15, 2022.