Detection of dual effects of degradation of perennial snow and ice covers on the hydrologic regime of a Himalayan river basin by stream water availability modeling

• Published in: Journal of hydrology (Amsterdam) 2012-01, Vol.412, p.14-33
• Main Author: Mukhopadhyay, Biswajit
• Format: Article
• Language: English
• Subjects: Basins; Climate change; Degradation; Earth sciences; Earth, ocean, space; Exact sciences and technology; Freshwater; Himalaya; Hydrology; Hydrology. Hydrogeology; Karakoram; Mathematical models; Mountains; Perennial snow and ice covers; River basins; Streams; Summer; Upper Indus Basin; Water availability model
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/j.jhydrol.2011.06.005

► A monthly river flow model of Upper Indus Basin with MODIS derived snow covered areas. ► Perennial snow/ice covers within the Upper Indus Basin has decreased in recent years. ► Decrease in perennial snow/ice covers has dual effects on river flow characteristics. ► Decrease in discharge rates during the peak melting season (June–August). ► Shift of peak discharge period from July/August to late spring/early summer (May/June). In river basins where melt water from snow and ice constitutes a dominant component of stream discharge during summer, degradation or reduction of perennial snow and ice covered areas ( SCA P ) has a profound effect on stream water availability in those basins. Degradation of SCA P that includes glaciers is a globally widespread phenomenon observed in the recently past decades; its cause has been attributed to global warming and its consequence is expected to dramatically alter the flow regimes of the rivers draining the terrains. The predicted change in flow regime is an initial increase in summer flows in the early decades of 21st century followed by sharp decline of the same during the later parts of the century. Estimation of SCA P within the Upper Indus Basin (UIB), straddling the western ranges of the Greater Himalayas, Karakoram Mountains, and the eastern mountain ranges of the Hindu Kush, shows that from 1992 to 2010 there has been about 2.15% reduction in SCA P . A spatially distributed basin-scale stream water availability model is presented to calculate monthly river discharges at critical hydrologic junctions within UIB. Model calculations for the years 1992, 2000, and 2008, show that due to the degradation of the SCA P within the basin, there has been significant decrease in summer discharges at various hydrologic junctions. The percentage decline in flows varies from 10% to 22%, depending on the locations of the junctions within the basin. The space-dependence of these variations reflects differential degradation of SCA P in various parts of the basin. Furthermore, the time of peak discharge at all of the hydrological junctions has shifted from middle/late summer to late spring/early summer as another outcome of SCA P reduction. Such temporal shifting of nival regimes to early part of warmer season has also been predicted by global warming models. However, the case study presented here for a major Himalayan river basin demonstrates that such shifting of peak discharge in the time domain can also take place simply due to