Over the past six months, variations in the intensity and locations of western disturbances have brought heavy rainfall to Delhi during some months, and kept the city dry and in the grip of a heat wave at other times.
Western disturbances explained
A western disturbance is an extratropical storm originating in the Mediterranean regionthat brings sudden winter rain to the northern parts of the Indian subcontinent.
It is a non-monsoonal precipitationpattern 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 a global phenomena with moisture usually carried in the upper atmosphere, unlike their tropical counterparts where the moisture is carried in the lower atmosphere.
Western disturbances are more frequent and stronger in the winter season.
Western disturbances are important for the development of the Rabi crop ,which includes the locally important staple wheat.
Western disturbances are usually associated with cloudy sky, higher night temperatures and unusual rain.
Excessive precipitation due to western disturbances can cause crop damage, landslides, floods and avalanches.
Over the Indo-Gangetic plains, they occasionally bring cold wave conditions and dense fog.
