Correct Option
The correct option isLonger dry spells in the plains and widespread rain in the mountainous catchment areas.
Explanation
The Monsoon Trough is an elongated low-pressure area extending from the heat low over Pakistan to the head of the Bay of Bengal. Its position oscillates north and south during the southwest monsoon season, serving as a primary determinant for the spatial distribution of rainfall over the Indian subcontinent.
Analysis of the Phenomenon
When the axis of the monsoon trough shifts northward and aligns close to the foothills of the Himalayas, the weather pattern changes drastically:
- Dry Spells in the Plains: The displacement of the low-pressure zone away from the Ganga plains results in a significant reduction or cessation of rainfall in the plains of North India. This condition is technically referred to as a "break" in the monsoon.
- Heavy Rainfall in Mountains: The moisture-laden winds are directed towards the Himalayan foothills. Consequently, widespread and heavy rainfall occurs in the mountainous catchment areas of the Himalayan rivers.
- Hydrological Consequence: The intense rainfall in the upper catchment areas often leads to severe flooding in the river basins (such as the Brahmaputra and Kosi), even while the surrounding plains experience drought-like conditions.
Therefore, the shift results in longer dry spells in the plains and widespread rain in the mountainous catchment areas.
Key Takeaway: A northward shift of the monsoon trough towards the Himalayas triggers "break monsoon" conditions, characterized by dry plains and heavy precipitation in the Himalayan foothills and river catchment areas.