The rainfall distribution pattern over the Ganga basin decreases from the

The rainfall distribution in the Ganga basin is primarily governed by the Bay of Bengal branch of the South-West monsoon. Precipitation decreases from east to west because the moisture-laden winds lose their water content as they move inland from the Bay of Bengal toward the western plains. Specifically, annual rainfall drops from approximately 1600 mm in West Bengal to about 800 mm in western Uttar Pradesh and Haryana. Additionally, rainfall decreases from north to south within the basin. The northern Ganga plain, situated along the sub-Himalayan foothills (Tarai belt), receives higher rainfall (100–200 cm) due to orographic lifting by the Himalayas [2]. In contrast, the southern parts of the plain, moving toward the peninsular plateau, generally receive less precipitation. Thus, the gradient follows a decreasing trend from the humid east to the semi-arid west and from the mountainous north to the southern plains.

Sources

1. [1] INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.) > Chapter 4: Climate > Distribution of Rainfall > p. 38
2. [2] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 4: Climate of India > VARIABILITY OF RAINFALL > p. 31