N. Gopal Raj
Glaciers that feed the seven great rivers of Asia Ganga, Indus, Brahmaputra, Salween, Mekong, Yangtze, and Huang Ho are under threat.
AS THE world warms inexorably, glaciers in the Himalayas are melting away, putting at risk freshwater supplies for millions of people in Asia.
The 33,000 sq km of glaciers amidst some of the world's highest mountains form the largest concentration of glaciers outside the polar ice caps. These glaciers, which release an estimated 8.6 million cubic metres of water annually, have nourished seven great rivers of Asia Ganga, Indus, Brahmaputra, Salween, Mekong, Yangtze, and Huang Ho. Ancient civilisations sprang up and thrived along the shores of these rivers.
But now the pace of global warming is threatening the very existence of the Himalayan glaciers. Since the mid-1970s, the average air temperature measured at 49 stations of the Himalayan region rose by one degree Celsius, with high elevation sites warming the most, noted a report compiled in 2005 by WWF, the global conservancy organisation. "This is twice as fast as the 0.6 degrees Celsius average warming for the mid-latitudinal northern hemisphere over the same period and illustrates the high sensitivity of mountain regions to climate change," added the report.
The Himalayan glaciers could disappear in the coming decades and the once perennial rivers turn into seasonal ones, noted the Intergovernmental Panel on Climate Change (IPCC) in the final draft of its report on the impact, adaptation and vulnerability produced by global warming.
"In the course of the century, water supplies stored in glaciers and snow cover are projected to decline, reducing water availability in regions supplied by meltwater from major mountain ranges, where more than one-sixth of the world population currently lives," according to a summary of the report that the IPCC released on April 6. Waters from the melting glaciers would also contribute to rising sea levels, which the IPCC warns would devastate many coastal areas and affect millions of people around the world by 2080.
Longer ablation periods
Himalayan glaciers are very vulnerable to climate change, says Syed Iqbal Hasnain, a leading glaciologist who is currently with the Centre for Policy Research in New Delhi. It is not just that higher temperatures lead to more ice turning to water. The "ablation period" when the glaciers melt in summer has lengthened. Earlier, by October-November it would start snowing. In recent years, it is still often quite warm during those months and the snows set in only later in winter, he remarked.
The late snows produce another problem. The snowflakes need several months to turn into hard ice crystals. Without the time needed for such transformation, more of the glacier is liable to melt when summer comes, Dr. Hasnain told this correspondent.
The south-west monsoon that brings torrents of rain to the plains of India deposits snow on the upper reaches of mountains in central and eastern Himalayas. But climatic changes have led to rain, rather snow, falling even at higher elevations during the monsoon and this could accelerate the melting of glaciers, he added.
In the face of these threats, the Himalayan glaciers are receding alarmingly. Several studies have indicated that the rate at which these glaciers are retreating has accelerated in recent decades. The Gangotri glacier, whose melted waters feed the river Ganga, has, for instance, been receding since 1780 but its rate of retreat has tripled in the last three decades.
Anil Kulkarni of the Indian Space Research Organisation's Space Applications Centre in Ahmedabad and fellow researchers used satellite pictures to study 466 glaciers in the Chenab, Parbati, and Baspa basins. These glaciers had covered 2,077 sq. km in 1962. But by 2001-2004, the area occupied by these glaciers had shrunk by 21 per cent, reported the scientists in a paper published earlier this year. As the glaciers retreated, they also became more fragmented and therefore more vulnerable to the affects of global warming.
French and Indian scientists have been studying glaciers in the Spiti-Lahaul region of Himachal Pradesh. In a paper published recently, the scientists found that the glaciers, which occupied some 900-odd sq. km., had experienced "significant thinning at low elevations" between the fall of 1999 and November 2004. Worse still, the rate of ice loss in the glaciers during that time was about double the average for the Himalayas between 1977 and 1999. This indicated "an increase in the pace of glacier wastage," observed the scientists in their paper. However, in an email, Etienne Berthier, the first author of the paper, noted that the survey period had been short and further monitoring was required to assess a long-term trend.
A modelling exercise carried out by the Centre for Ecology and Hydrology in Britain found that as the Himalayan glaciers melted in the face of global warming, there would initially be an increase in river discharges, which could produce widespread flooding, and then the river flows would decline. The model studies indicated that flows in rivers originating in the western Himalayas could peak in 2050 and in 2070 for rivers originating in eastern Himalayas, according to Rajesh Kumar of the Birla Institute of Technology extension centre in Jaipur, who was involved in the study.
"Glacier melt in the Himalayas is projected to increase flooding, rock avalanches from destabilised slopes and affect water resources within the next two to three decades," according to the latest IPCC summary report. This would be followed by decreased river flows as the glaciers receded, it added.
Scientists have estimated that melting snow and glaciers provides up to 80 per cent of the dry season flows of the Indus, Ganga, and Brahmaputra rivers in the lowlands. As these river flows fall, agriculture, water supplies on which millions of people depend, and power generation will be badly affected.
Glacial retreat in the Himalayas, along with possible changes in monsoon rainfall as a result of climate change, would have far-reaching consequences for water availability in the South Asian region, points out Prakash Rao, senior coordinator for the climate change and energy programme at WWF India. Water-sharing disputes within and between countries in the region, that were already proving troublesome, could worsen as a result, he told The Hindu.