Question

Give reasons for the following.

Patna receives more rainfall than Lucknow during the southwest monsoon season, but the rainfall is less than the rainfall received by Kolkata during the same season.

Answer 1

1. Distance from the Oceanic Source: The Bay of Bengal monsoon enters India via the east coast. Kolkata is the coastal city nearest to the marine moisture supply, Patna is further inland, and Lucknow is deep in the interior.
2. Sequential Moisture Depletion: As rain-bearing winds travel westward up the Ganga Valley, they continuously release precipitation. The winds are heavily saturated in Kolkata, lose a significant amount of moisture by the time they reach Patna, and are nearly exhausted by the time they reach Lucknow.
3. Funneling Effect of the Mountain Barriers: The Himalayan range traps the monsoon branch and forces it to move parallelly from east to west along the plains. Since the winds must pass Kolkata and Patna before ever reaching Lucknow, the eastern cities naturally intercept the heaviest initial cloud downpours.
4. Variations in Relative Humidity: Due to its coastal proximity, Kolkata has the highest relative humidity, which causes quick condensation and increased cloud formation. As you move westward into Lucknow, the air becomes increasingly dry, making it difficult for enormous, rain-heavy clouds to sustain themselves.