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 21^st Century on discharge, precipitation and temperature measurements around the basin. The studies found that an increase in air temperature by 0.5^oC 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 1.5^oC 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.