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Why does the Ganges River have much higher flow during the summer monsoon?

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Physical map showing the Brahmaputra and Ganges river basins and their drainage networks across northern India, Bangladesh, Nepal, Bhutan, Tibet (China), and Myanmar. The map uses color shading to indicate elevation, from the high Himalayas in brown and white to lowland plains in green, and marks major rivers, tributaries, glaciers, dams, irrigated areas, and regions subject to flooding. An inset locator map highlights the region within South Asia. — Ganges River The Brahmaputra and Ganges river basins and their drainage network.

The Ganges River experiences a significantly higher flow during the summer monsoon primarily due to the heavy rainfall brought by the southwesterly monsoon winds, which typically occur from July to September.12

During this period, the Bay of Bengal branch of the monsoon is diverted westward by the Himalayan barrier, moving up the Gangetic Plain and delivering substantial precipitation across the river's basin. Additionally, the river's volume is bolstered during the summer months because the glaciers in the Himalayas provide their greatest amount of meltwater to the river system during this same timeframe. These combined factors—intense seasonal rainfall and increased glacial melt—result in the river's marked seasonal variation in flow and frequent floods during the rainy season.1342