WESTERN DISTURBANCE

Subject : Geography

Context : Rain lashed Delhi and NCR on Sunday morning, leading to a drop in day temperatures amidst strong winds and thunderstorm.

Concept :

According to IMD , the effect of the western disturbance over the region is expected to start waning and only light rain is expected during the day, after which the sky is expected to clear, paving the way for another spell of fog in the mornings.

Western Disturbances

Western Disturbances are low pressure systems, embedded in western winds (westerlies) that flow from west to the east.
It is a term coined by an Indian Meteorologist for the weather phenomenon which is propagated from the West.
Western Disturbances begin is a low pressure system that originates in the Mid- latitude region near the Atlantic ocean and Europe.
The low pressure typically forms over the Mediterranean Sea and travels over Iran, Iraq, Afghanistan and Pakistan before entering India loaded with moisture.
These moisture laden western disturbances eventually come up against the himalayas and get blocked, as a consequence, the moisture gets trapped and precipitation is shared in the form of snow and rain over Northwest India and sometimes, other parts of North India.
An average of 4-5 western disturbances form during the winter season and the rainfall distribution and amount varies with every western disturbance.
The word ‘Western’ refers to the direction from which they originate with regard to India.
The word ‘disturbance’ is used because the air within the low pressure systems tends to be unstable or disturbed.
Sometimes, when western disturbances become more intense in the Indian Region, they can extend even upto 15 degree north, resulting into rainfall upto north Maharashtra, Gujarat and the entire Madhya Pradesh to the south.

Impact

Western Disturbances are the cause of the most winter and pre-monsoon season rainfall across North-West India. This phenomenon is usually associated with cloudy sky, higher night temperatures and unusual rain. It is estimated that India gets close to 5-10% of its total annual rainfall from western disturbances.
In winter, western winds bring moderate to heavy rain in low lying areas and heavy snow to mountainous areas of the Indian subcontinent.
India is a rain dependent country and while the south west monsoon covers most of India, parts of North India don’t get much rain from it. These regions depend upon snow and rain from western disturbance during winter season from November to March.
Precipitation during the winter season has great importance in agriculture particularly for rabi crops including wheat, which is one of the most important Indian crops.
They start declining after winter. During the summer months of April and May, they move across North India and at times help in the activation of monsoon in certain parts of northwest India.
During the monsoon season, western disturbances may occasionally cause dense clouding and heavy precipitation.
Weak western disturbances are associated with crop failure and water problems across north India.
Strong western disturbances can help residents, farmers and governments avoid many of the problems associated with water scarcity.