Chapter 2: Review of Literature……………………………………………………... 9-52
2.4 Climate change and its impact on snow/glacier
Mountain glaciers play an important role to detect and monitor climate change in regions not typically monitored by instrumentation (Haeberli et al., 2007). The rate of warming in lower troposphere increases with altitude i.e. temperature increases more in high mountains than at low altitudes (Bradley et al., 2004). Again, mountain areas exhibit a large spatial variation in climate zones due to large differences in altitude over small horizontal distances. These
conditions make mountain areas more vulnerable to climate change (Beniston et al., 1997).
The change in climate and its impact on the extent of global snow covered and glacierized areas have been studied by many researchers around the world. Walcher (1773) was one of the first to propose the fact that glacier fluctuations are the result of variations in climatic conditions. Angstrom (1933) stressed on the importance of temperature, radiation and wind as agents for snow and glacier melting. Ahlmann (1935; 1948) derived the first empirical formula for the computation of ablation from known values of climatic parameters such as incident radiation, air temperature and wind velocity.
IPCC (2001a) reported that extent of snow cover has decreased by 10% since late 1960s.
Long-term records on glacier fluctuation indicating retreat of mountain glaciers support the change in climate in the past century (Letreguilly aand Reynaud, 1990). In contrast to this, some glaciers like Nigardsbreen (Norway) and Franz Josef Glacier (New Zealand) are in advancing trend (Oerlemans et al., 1998). However, an overall retreat of mountain glaciers has been observed in non-polar regions during the 20th century. According to Haeberli and Beniston (1998), the retreat extent of glacierization in the European Alps is reduced to 30- 40%, whereas the volume of ice has been reduced by 50% since the middle of the past century. Dyurgerov (2002) reported that melting of glaciers will accelerate in continental regions, North America, South America, Central Asia, sub-polar glaciers and will contribute to sea level rise.
If glaciers continue to retreat this way, many small mountain glaciers will disappear within the 21st century (Nesje et al., 2008). However, within a region, small and large glaciers retreat/advance at different rates (Granshaw and Fountain, 2006; Fountain et al., 2009) and past retreat and advances of a glacier may not indicate how that glacier will change in the future. In addition, because of the fact that climate change within a region is not typically spatially uniform, similar glaciers in different basins within the same region may not experience identical changes (Shindell and Faluvegi, 2009).
In a western Canadian mountain range, De Beer and Sharp (2009) found that 75 out of 86 small glaciers did not show noticeable size change during a similar time period. The lack of change implies that either this mountain region experienced no late 20th century warming or that the small glaciers did not respond to any warming. The authors stated that the lack of glacier change was due to small size and sheltered locations of glaciers which allowed them to be roughly in balance with late 20th century climate conditions. The interpretation of
climate change based on the behavior of small cirque glaciers is not always straightforward or unique (Bolch et al., 2010).
Brown et al., (2010) considered 11 different warming scenarios for Sperry glacier, Glacier National Park, Montana to study future change of glaciers under these warming scenarios.
The scenarios varied from no warming to warming at a linear rate of 10°C/century. They assumed constant precipitation and considered only the change invoked by warming. They derived a relationship between magnitude of temperature change and the sensitivity of the glacier to the change in temperature. Their result showed that under large magnitude warming, the glacier undergoes rapid area and volume reductions that are insensitive to minor variations to the warming rate. They concluded that a small change in climate would produce varying responses for glaciers throughout the region, whereas the glacier response to a large change in climate would likely to be very similar over the entire region.
2.4.1 Impact of climate change on Himalayan glaciers
Brahmaputra, Ganges and Indus are the three major river systems of Indian subcontinent which originate in the Himalayas and are expected to be much vulnerable to climate change because of substantial contribution from snow and glaciers (Singh et al., 1997a; Singh and Jain, 2002). During winter, a large extent of mountainous area of Himalayan river basins is covered by snow which starts ablating during summer causing huge discharge at the downstream of these rivers.
The snow cover in the Himalayas can be categorized as, temporary snow cover, seasonal snow cover and permanent snowfields or glaciers. Snow cover that stays for a few days and then melts away is termed as ‘temporary snow cover’. Such snow usually occurs at lower altitude during winter and sometimes at higher altitude during summer. Snow cover that is formed over weeks or months by consecutive snowfalls and then melts away during the following summer is termed as ‘seasonal snow cover’. The snow cover above a certain altitude that is carried over to the next winter season without melting during summer is termed as ‘permanent snowfields or glaciers’. The seasonal snowpack is more important in that it contributes to the water resources during lean summer months.
The Himalaya-Karakoram-Hindu Kush (HKH) along with the adjoining Tibetan Plateau and central Asian mountain ranges such as Tien Shan and Kunlun ranges of western China, have the most highly glaciated area and largest body of ice outside the polar region (Kulkarni et al., 2007). The glaciers and snowfields of the HKH mountain belts and Tibetan Plateau are
amongst the fastest receding glacial and snow cover in the world (Dyurgerov and Meier, 2005). According to Kulkarni et al., (2007) and Raina (2009), widespread fragmentation of glaciers has also degraded the total areal coverage of perennial snow and ice in this region.
Jain (2001) used SNOWMOD model to study the impact of warmer climate on melt and evaporation in the Satluj basin. They adopted three future temperature scenarios (T+1, T+2 and T+3°C). They found that under a warmer climate, melt was reduced from snowfed basins, but increased from glacierfed basins. For T+2°C scenario, annual melt was reduced by 18% for snowfed basin, while it increased by 33% for the glacierfed basin.
Afzal et al., (2014) used MODIS 8 day composite data to identify spatial-temporal trends in snow cover in the upper Indus basin from 2001 to 2005. For the same period, they analyzed the temperature data for upper Indus basin. They found that the snow cover of Indus basin showed an increasing trend from west to east. They also concluded that regional warming is affecting the hydrology of upper Indus basin due to accelerated glacial melting.