Western Disturbances

Context:

Several studies conducted by various scientific institutes in the country in regard to the impact of western disturbances during winter season on Indian climate

Western Disturbances

• A western disturbance is an extratropical storm originating in the Mediterranean region that brings sudden winter rain to the northwestern parts of the Indian subcontinent.
• It is a non-monsoonal precipitation pattern driven by the westerlies.
• The moisture in these storms usually originates over the Mediterranean Sea, the Caspian Sea and the Black Sea.
• Extratropical storms are global phenomena with moisture usually carried in the upper atmosphere, unlike their tropical counterparts where the moisture is carried in the lower atmosphere.
• In the case of the Indian subcontinent, moisture is sometimes shed as rain when the storm system encounters the Himalayas.
• Western disturbances are more frequent and strong in the winter season.
• Western Disturbances develop in the mid latitude region (north of the Tropic of Cancer), not in the tropical region, therefore they are called as mid latitude storms or extra-tropical storms.
• Extra-Tropical Cyclones are also called as winter storms and blizzards.
• 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.
• The phrase Western Disturbance was first used in a published literature in 1947. However, its precursor Winter Disturbance was coined earlier in 1931.

IMPACT OF WESTERN DISTURBANCES

There are several studies conducted by various scientific institutes in the country in regard to the impact of western disturbances during winter season on Indian climate. The studies show that;

• 30% of annual precipitation over North West Indian region (J & K, Ladakh, Himachal Pradesh &Uttarakhand) is received during winter and it is mostly associated with Western Disturbances. It also causes rainfall over the adjoining places of north India.
• Precipitation associated with Western Disturbances (WDs) influences Himalayan climate, glaciers, snow-water storage, flora, fauna, agricultural crops and human inhabitants etc.

The adverse weather elements associated with Western Disturbances are;

• Intense precipitation in the form of snow, rain or hail leading to landslides, avalanches and damage of agriculture and manmade structures.
• Dense to very dense fog events leading to interruption in aviation / rail / road transport services.
• Cold Wave to Severe Cold Wave and Cold Day to Severe Cold Day conditions after the passage of western disturbances.

However, precipitation from the western disturbances is very vital for the Rabi Crop over northwest India. Also snowfall/snowmelt in the Hilly regions contribute to river flow and drinking water for people living downstream.

• India Meteorological Department (IMD) issues forecast & warnings for the weather elements related to WD also. From National Weather Forecasting Centre (NWFC), IMD forecasts are given in sub- divisional scale whereas the Regional Weather Forecasting Centre (RWFC) and State Weather Forecasting Centre (SWFC) issue forecast and warnings in district level and station level.