THE NANO-KOSI WATERSHED, CENTRAL HIMALAYA, INDIA .2. HUMAN IMPACTS ON STREAM RUNOFF

This report is a follow-up to the paper with a similar tide, Part I: Sediment Load, published in Volume 14, No. 1 of this journal. The two-year reconnaissance study in the Nana Kosi watershed in the Indian Kumaun Himalaya determined that in the most disturbed agricultural land 60% of the annual runoff occurred in July, the month of heaviest rainfall. However, under natural conditions in the oak and pine forest only about 23% of the total annual flow occurs in July. In April, the driest, hottest month, measurements indicate high amounts of runoff (308 m3 km-2 yr-1) in the least disturbed oak and pine forest, while runoff amounts were low (108 m3 km-2 yr-1) in the most disturbed agricultural land. The seasonal budget has also changed due to human impact: in the agricultural area, 81% of the total annual runoff occurs in the rainy season, compared to 53% in the forest. Measurements suggest that the annual runoff has been reduced by about 50% due to anthropogenic change.