Why does the sub-Himalayan region of West Bengal receive more rainfall than Kolkata?

The sub-Himalayan region of West Bengal receives significantly more rainfall than Kolkata primarily due to the influence of the Himalayas on the southwest monsoon winds.12

As the moisture-laden Bay of Bengal branch of the monsoon sweeps across the region, it encounters the steep terrain of the eastern Himalayas. The mountains act as a physical barrier, forcing the air to rise, cool, and condense, which results in heavy precipitation on the windward slopes. This orographic effect is a key factor in the high rainfall totals observed in areas like Darjeeling, where annual precipitation is substantially higher than the approximately 64 inches (1,625 mm) recorded in Kolkata. In contrast, Kolkata is situated in the southern Gangetic Plain, where the monsoon winds do not undergo the same degree of forced uplift, leading to lower annual rainfall totals compared to the northern mountainous tracts.23415