A Western Disturbance (WD) is an extratropical storm system originating in the Mediterranean region, which brings rain and snowfall to northwestern and northern India during winter and early spring. The term “disturbance” refers to an area of low pressure accompanied by cloudiness, precipitation, and sometimes thunderstorms.
Origin and Movement
- Source:
Western Disturbances develop over the Mediterranean Sea, Caspian Sea, and Black Sea due to the interaction of westerly jet streams with frontal systems. - Path:
These systems travel eastward across Iran, Afghanistan, and Pakistan, before reaching India, guided by the subtropical westerly jet stream. - Entry Point into India:
They typically enter through Jammu & Kashmir and move towards Himachal Pradesh, Uttarakhand, Punjab, Haryana, Delhi, Rajasthan, and occasionally up to Uttar Pradesh and Bihar.
Weather Effects
- Rainfall and Snowfall:
Bring winter rain to the northwestern plains and snowfall to the Himalayan states. - Temperature:
Lead to moderate warming during cloudy periods and sharp cooling after passage due to clear skies. - Agricultural Importance:
Crucial for rabi crops, especially wheat and mustard, as the rainfall replenishes soil moisture. - Adverse Impacts:
Occasionally cause hailstorms, fog, and crop damage, especially if they occur near harvest time.
Seasonal Occurrence
- Peak Months: December to April.
- Frequency: On average, 4–6 WDs per month during winter.
Mains Question:
Explain the significance of Western Disturbances in determining the winter weather pattern of north India and their implications for agriculture.