Kullu: Climate change is altering the hydrology of the Satluj basin, with shrinking Himalayan glaciers posing long-term risks to hydel generation in Himachal Pradesh, reveals a new study.‘Impact of Climate Change on Water Flow Pattern Affecting the Generation of Hydropower Projects’, a study by Himachal Pradesh’s State Centre on Climate Change (SCCC), analysed glacier dynamics, snow cover, glacier mass balance and river discharge in the Satluj basin using multi-temporal satellite imagery, remote sensing, GIS and hydro-meteorological data spanning two decades.According to the study, the total glacier-covered area across the Satluj basin reduced from 1,481.7 square kilometres in 2000 to 1,384.2 square kilometres in 2020.The report says more than 80% glaciers in the basin are retreating. It identified 1,005 retreating glaciers and glacierets in the four sub-basins of the Satluj basin — Spiti, Baspa, Lower Satluj and Upper Satluj. While 800 glaciers were retreating at rates below 10 metres annually, 155 were retreating at 10-20 metres per year, 44 at 20-40 metres per year, and six at more than 40 metres per year. The most rapid retreat, observed in the Spiti sub-basin, was 73.7 metres per year.The retreat is particularly pronounced in the Upper Satluj and Spiti sub-basins.The study mapped 1,699 glaciers in 2000, 1,632 glaciers in 2011 and 1,709 glaciers in 2020. However, the study emphasised that the increase in the number of glaciers does not indicate glacier growth. Instead, it reflects the fragmentation of larger glaciers into smaller, separate ice bodies — an evidence of rapid climatic changes. As glaciers retreat, tributary glaciers become disconnected from larger valley glaciers and are mapped as separate glaciers, increasing the total count while overall glacier area continues to decline.The study also documented widespread deterioration in glacier health. The study assessed glacier mass balance in 2000, 2011 and 2020 and found the number of glaciers with negative mass balance rose from 565 in 2000 to 875 in 2020.A negative mass balance means glaciers are losing more ice through melting than they gain through snowfall accumulation.The report blames this on rising temperatures, earlier melting and reduced winter snow accumulation. It states that continued negative mass balance will reduce glacier storage over time, affecting long-term water availability.Snow cover analysis carried out using satellite imagery between 2010 and 2020 also revealed considerable seasonal and interannual variability. The study found that snow cover across the Satluj basin fluctuated between 35% and 72%, indicating substantial year-to-year changes in winter snow accumulation.Researchers also found evidence that the duration of snow cover is becoming shorter because of earlier spring snowmelt and delayed winter snowfall, affecting glacier accumulation.The report states that rising temperatures now exert greater influence on meltwater generation, resulting in changes in the seasonal pattern of river flows.Increased glacier melting may enhance river discharge, but the report warns continued glacier loss will ultimately reduce the contribution of glacier melt to river flow. As glacier storage diminishes, late-season water availability is expected to decline, states the study.According to the report, major hydropower projects in the Satluj basin, including Nathpa Jhakri (1,500 MW), Karcham Wangtoo (1,091 MW), Rampur and Bapa II project, may initially benefit from higher inflows due to increased glacier melt. However, shrinking glaciers are expected to reduce long-term water availability, while higher sediment loads from accelerated erosion could lead to reservoir siltation, turbine abrasion, increased maintenance costs and operational challenges.The study says run-of-the-river and small hydropower projects are likely to be more vulnerable because they depend directly on river discharge and have little or no storage capacity. Changes in the timing and volume of river flows, coupled with increased sediment transport, could reduce generation during lean-flow periods, increase turbine wear and require more frequent maintenance.
