Other than the polar regions, the Himalayas follow as the largest deposit of frozen water in the world, especially in the case of Himalayan glaciers. Himalayan glaciers make up about 17 per cent of the Himalayas and about 37 per cent of the Karakoram Range.
The water melted from Himalayan glaciers form the headwaters for many major river catchments in the Indian subcontinent. This discharge of headwater makes up for about 70 to 80 per cent of the melting of snow and ice from the highlands. In such a scenario, global warming and climate change can have significant impacts on the flow of water into river catchments.
Climate Change Impacts in the Tibetan Plateau
Consisting of enormous amounts of snow and ice, the Tibetan Plateau is sometimes referred to as The Third Pole and also The Water Tower of Asia and holds the Hindu Kush Himalayan Ice Sheet – the world’s largest ice mass outside the two poles. The Tibetan Plateau has more than 45,000 Himalayan glaciers that cover a total area of more than 105,000 sq km. The Tibetan Plateau is the highest region on Earth with an average elevation of about 4,500 m above sea level and covers an area of about 2.5 million sq km (Norbu, 2011). The Tibetan Plateau has the Himalayas in the south, the Kunlun Range across the north and the Karakorum Range towards the west.
The largest river run-off out of any location in the world occurs from the rivers originating from the Tibetan Plateau that are fed by melting glaciers. In the summer months about 70 per cent of the headwater in the Ganges for example is fed by glaciers from the Tibetan Plateau. As such, with climate change water supply and drainage is expected to be severely affected due to its effects on melting glaciers, with India particularly affected by headwater discharge from the Himalayas.
Unlike Arctic and Antarctic permafrost, the permafrost prevailing in the Tibetan Plateau is alpine permafrost. This sort of permafrost tends to be warm permafrost combined with rich ground ice and this makes areas covered by this form of permafrost very vulnerable to global warming and climate change.
It is estimated that about 12,300 million tonnes of carbon are stored in the alpine permafrost of the Tibetan Plateau (Norbu, 2011). This can potentially become a major source of methane emissions – a greenhouse gas. The melting of permafrost in the Tibetan Plateau can occur in a vicious cycle whereby warming might induce more melting and the corresponding release of greenhouse gases.
Although the vegetation in the Tibetan Plateau can act as major carbon sinks in the region, the ecosystem in the Tibetan Plateau is undergoing major changes due to global warming. The glaciers here are receding, numerous lakes are shrinking or disappearing, wetlands are drying up, permafrost is thawing, and the headwater discharge in many rivers is becoming lesser. Also abnormal phenomena are being observed, such as non-sequential rainfall, reduced growth of young livestock, delays in the milking season for cattle, etc.
It is also observed that the thaw in the spring season is occurring earlier, which is causing the permafrost to melt faster than the plants can access the water – leading to a loss of wetlands. It is expected that an increased rate of evapo-transpiration due to global warming can also intensify the desertification process in the Tibetan Plateau and adjoining regions (Klein, 2005). Desertification can adversely affect vegetation as carbon sinks and also the carbon sequestration properties of moisture and permafrost. The prospects for environmental degradation however, can be multi-faceted, with the principal threats being glacial retreat, desertification and the melting of permafrost.
The Impacts of Himalayan Glaciers on River Catchments
Contradicting reports by the Intergovernmental Panel on Climate Change (IPCC), Thayyen and Gergan (2009) argue that glacial retreat in the Himalayas will not necessarily result in greater headwater flow into Himalayan river catchments. Arguing that the previous view focuses only on glacial outlets, they cite Hasnain’s (2008) paper who observed that the adverse effect was in fact glacial shrinkage due to global warming that can in turn cause a high run-off. This however also could reduce the overall capacities of Himalayan glaciers to provide headwater.
Hasnain comments on the reduction in glacial dimensions with climate change and states that Himalayan glaciers as a water source cannot be assumed as permanent. He observes that Himalayan glaciers would need to maintain a specific mass balance of between 90 and 78 cm to prevent large scale loss of glacial ice. However, Himalayan glaciers are losing ice, and this could pose a serious threat to the availability of water in India and in adjoining regions linked to Himalayan river catchments.
Hasnain’s studies point towards that fact that Himalayan glacial run-off has increased in the recent past and shall continue to advance with the increase in glacial shrinkage. With enough glacial shrinkage, Hasnain expects significant decreases in the headwater discharged to river catchments. River catchments affected by headwater discharges from Himalayan glaciers such as the Ganges, Brahmaputra and Indus catchments are expected to greatly affected by glacial shrinkage, along with a host of other river systems drawing water from Himalayan glaciers. This could have severe implications for the discharge and availability of fresh water in areas fed by these river catchments.
Case Study: Hydrology of the Bhagirathi-Ganga Basin
The Bhagirathi river is one of the principal tributaries of the river Ganges and arises in the Gangotri glacier Goumukh. It forms a moauntainous catchment with the Ganges until it joins the Alaknanda, another tributary, at Devprayag to join with the river Ganges. The basin comprises water from 238 glaciers with a total ice volume of about 67.02 cu km. The average Monsoon precipitation in the headwaters for this basin is between 1,000 and 2,500 mm (Hasnain, 2008).
Investigations into the Dokriani Glacier were carried out by the Department of Science and Technology, GoI since the 1990s till the early 21st Century on discharge, precipitation and temperature measurements around the basin. The studies found that an increase in air temperature by 0.5oC since 1998 in the Dokriani Glacier valley had led to significant melting of glacier ice. Anomalouly high melting of the glacier has occurred due to excessive warming which has led to high run-off of glacial headwater, with an increasing rate of discharge.
The mass balance of the glacier was negative, with 80 per cent melting for the period. It is expected that with an increase in temperature by 1.5oC and an increase in Monsoon precipitation by 60 per cent, the seasonal run-off during the Monsoon season will increase to 100 per cent, which can severely deplete the glacier. The possible effects according to the research point towards reduced accumulation of snowfall, an increase in ablation due to heat, and reduced albedo due to the decrease in snowfall. If the run-off increases to 100 per cent, this can also lead to a decrease in the supply of fresh water in the basin due to inadequate replenishment of glacial ice, which can have significant implications for ecologies and lives downstream.