CBSE Class 9 Answered

Due to excessive solar radiation, low pressure area develops over north west India. As monsoon arrives in the region, this low pressure area extends towards the east and forms an elongated low pressure zone which almost runs parallel to the Great Himalayas in a west to east direction. This is referred as ‘Monsoon trough’.

The trough (Inter Tropical Convergence Zone) moves periodically to the north and south of its normal position. It affects the distribution of rainfall in India. When the trough move towards the north lying closer to the foothills of the Himalayas, the pattern of rainfall changes. The distribution of rainfall over the northern parts becomes scarce and the northeastern parts of the country lying closer to the foothills of the Himalayas receive abundant rainfall. This is also known as the breaks in the Monsoon rainfall.

Thus, due to the Monsoon trough while the northern parts of the country hardly receive rainfall during this period, the north eastern parts gets excessive rainfall and experience floods as most of the rivers originate in the Himalayan region.