Climatic Variation and River Flows in Himalayan Basins Upstream of Large Dams

Abstract:

High specific discharges from Himalayan headwater basins feed major reservoirs generating hydropower and supplying water to irrigation schemes across the Punjab plains of north-west India and Pakistan. Flow arises from seasonal winter snow cover, summer monsoon precipitation and melting glacier ice in varying proportions and differing absolute quantities along west –east axes of the Karakoram and western Himalaya. Discharge records for stations above Tarbela (Indus), Mangla (Jhelum), Marala (Chenab) and Bhakra (Sutlej) dams have been examined for periods between 1920 and 2009, together with precipitation and air temperature data for stations with long records (within the period 1893 to 2013) at elevations between 234 and 3015 m a.s.l. Ice-cover age in the basins above the dams was between 1 and 12 %. Flows in the Sutlej, Chenab and Jhelum reached maxima in the 1950s before declining to the 1970s. Flow in the Chenab and Jhelum increased to 1950s levels in the 1990s, before falling steeply into the 2000s mimicking variations in winter and monsoon precipitation. Discharge in the Indus at Tarbela increased from the 1970s, reaching a maximum in the late 1980s/early 1990s, before declining back to 1970s levels in the 2000s, flow being influenced not only by precipitation fluctuations but also by changes in air temperature affecting glacier melt in headwater basins. Runoff at Bhakra was augmented by flow from the Beas-Sutlej link canal after 1977, but natural flow in the Sutlej above Luhri reduced considerably from the 1990s influenced by declining flows in the relatively dry but large Tibetan portion of the basin area. Large year-to-year fluctuations of reservoir inflows are nonetheless based on significant sustained underlying discharge levels at all four reservoirs.