Effect of orography on precipitation in the western Himalayan region

The present study deals with precipitation distribution with altitude for the Satluj and Beas basins in the western Himalayas. Rainfall increases linearly with elevation for both basins in the outer Himalayan range. The middle Himalayan range of the Beas basin has exceptionally heavy rainfall on the windward side and much less rain (less than half) on the leeward side, Rainfall gradients are 106 mm per 100 m to windward and 13 mm per 100 m to leeward of this range. Different trends of rainfall variation with elevation are observed in different seasons in the middle Himalayan range with a linear increase in annual rainfall. Rainfall follows an exponential decreasing trend with altitude in the greater Himalayan range. Average annual rainfall decreases from the outer Himalayas to the greater Himalayas in the Satluj basin. In the greater Himalayas, it is about one-sixth of outer Himalayas rainfall. Maximum rainfall is in the middle Himalayan range in the Beas basin. Monsoon rainfall contributes the largest part of the annual rainfall for all the Himalayan ranges. Spatial correlation is higher in the outer Himalayas range than in the other ranges. Snowfall increases linearly with elevation in the greater Himalayas. Snowfall gradients for the Spiti and Baspa sub-basins are 43 mm per 100 m and 10 mm per 100 m, respectively. The ratio of snowfall to annual precipitation varies linearly with altitude. All stations recorded more than 60% snow contribution to annual precipitation. Extrapolation of the relationship indicates that snow and rain contribute equally al about 2000 m, and all the precipitation occurs as snow above 5000 m.