The Ganga’s Hydrology - The Ganga: Water Use in the Indian Subcontinent - page 23

Though the average rainfall over India is one of the highest in the world for a country
of comparable size, it fluctuates widely in various regions. Because of heavier inten-
sity of rainfall, the annual run-off from the region, north of the Ganga, is 0.75 m and
that from the south is only 0.3 m, which makes the contribution of flow from the
northern tributaries significantly more than that from southern tributaries. Nearly
60% of the water, flowing in the Ganga, comes from areas, north of its course.
Peninsular streams together contribute the remaining 40%, though the catchment
extends over 60% of the entire Ganga sub-basin. Thus, hydro logically, Himalayan
rivers are of more importance than peninsular streams of the sub-basin (Fig. 4.1).
Distribution of rainfall on India is erratic and haphazard. Though the average
annual rainfall over the entire country is about 105 cm, it varies widely from region
to region. Over the Khasi and Jayantia Hills, it is about 1,000 cm, while toward
north, in the Brahmaputra Valley, it is as low as 200 cm. On the west coast, about
600 cm of rains fall on the windward side of the Western Ghat hills and only
50-60 cm fall on the leeward side of the Ghat hills; the distance between the two
is about 80 km. Such wide variations do not occur in plains beyond hilly regions.
Similar phenomenon is noticed on the east coast where rainfall is highest near the
coast but much less inland. On Aravalli ranges in north India, about 160 cm of rains
fall in a year but only 60 cm fall on the surrounding plains. Similarly, in the northern
plains, rainfall varies widely from 150 cm in West Bengal to about 15 cm in west
Fig. 4.1 Distribution of Ganga basin components