Changing streamflow patterns in the rivers of northwestern Himalaya : Implications of global warming in the 20th century

Abstract

The results of trend analyses of the discharge data of four rivers in northwestern Himalaya, namely Beas, Chenab, Ravi and Satluj, are presented here and the impact of climate change in the last century is discussed. In the case of Satluj river, studies indicate an episodic variation in discharge in all three seasons on a longer timescale of about 82 years (1922–2004). Statistically significant decrease in the average annual and monsoon discharge and insignificant increase in winter and spring discharge, despite increasing temperatures during all the three seasons can also be seen. Decreasing discharge during winter and monsoon seasons in the post-1990 period, despite rising temperatures and average monsoon precipitation strongly indicates decreasing contribution of glaciers to the discharge and their gradual disappearance. On a shorter timescale of the last four decades of the 20th century, barring the Beas river, which shows a significantly decreasing trend, the other three rivers have shown a statistically insignificant change (at 95% confidence level) in their average annual discharge. Annual peak flood discharges show significant increasing trends in the Satluj and Chenab basins, significant decreasing trend in the Beas river and insignificant trend in the Ravi river. Notwithstanding these variations, the studies indicate an increase in the number of ‘high-magnitude flood’ events in the rivers in northwestern Himalaya in the last three decades.