Pakistan is likely to face a major water crisis - flood and drought - in the next 20-50 years owing to unusually fast depletion of the Himalayan glaciers and other related uncertainties.
Sources cited some reports that indicated that the Himalayan glaciers, contributing over 80 per cent water to river Indus that fed more than 65 per cent of the country's agriculture, were receding at a rate of 30 metres to 50 metres annually. The Himalayas contain world's third largest ice mass after Antarctica and Greenland.
A recent report of the Earth Policy Institute, a distinguished organization, said that most Himalayan glaciers had been thinning and receding over the past 30 years, with losses accelerating to alarming levels in the past decade.
Fresh findings had sparked a debate among policymakers whether to shelve a dam on river Indus or build it quickly to save the water running down to the sea, sources said.
Director-General of the Pakistan Meteorological Department) Dr Qamaruz Zaman Chaudhry said that various scientific reports mention "a number of uncertainties because the glaciers are melting fast".
He said that some of the scientists, who had noticed the retreating trend of glaciers, indicated that the depletion was occurring faster on the Eastern side by comparison with the Western side of Himalayas that fed Pakistan's rivers.
He said that the higher pace of glacier melting could trigger huge water flows 20 years from now but could cause severe drought in the next 20 to 25 years. The chief of the meteorological department said that most scientists agreed that glaciers were melting at a faster rate because of global warming.
He said that the meteorological department had recently briefed the chairman of the Technical Committee on Water Resources A.N.G. Abbasi about the Himalayan glacier situation.
He said that he favoured the development of a major water reservoir on river Indus, preferably at Kalabagh because Bhasha dam would need a longer gestation period and heavy resettlement and construction costs.
The meteorological department, he said, had also provided a detailed report on impact of climate change on Indus river flow and the glacier's eco-hydrology. He said that the report had categorized the Himalayan mountain system as one of the youngest, most sensitive and interactive atmosphere-snow-land-ocean mountain system on the planet. The Himalayan snow-glacier system formed the tallest water tower.
The report said that the average annual water flow in the river Indus had been about 34 million acre-foot (MAF) for the period of 1975-90 despite a wet spell that increased the discharge by more than 40 per cent to an annual average of 51.16 MAF.
Mr Chaudhry agreed that glaciers could also 'burst' as a result of the higher snow melting rate. The glacier movement, he said, sometimes resulted in the formation of snow dams, which could burst and result in floods.
Dr Chaudhry said that the movement of glaciers had developed into a snow dam a few years ago upstream of Tarbela dam which was artificially broken by the PMD within a few days of its formation before it could block alarming level of water.
The PMD report said that Himalayan snow and ice region covered an area of 4.6 million square kilometres above 1,500 metres, 3.2 square kilometres above 3,000 metres and 0.56 square kms above 5,400 meters.
Talking about the distribution of permanent snow and ice in the Himalayan region, the report said that glaciers covered between 10 and 20 per cent of the total surface area, seasonal snow cover was 30 to 40 per cent of the surface area and melt-water contribution diminishes from west to east, being the greatest in the Indus basin.
The EPI report said that on Mount Everest, the glacier that ended at the base camp of Edmund Hillary and Tenzing Norgay, first men to reach the summit, had retreated five kilometres (three miles) since their 1953 ascent. Glaciers in Bhutan are retreating at an average annual rate of 30 to 40 metres. A similar situation is found in Nepal.
The report said that as glaciers melted, they were rapidly filling glacial lakes, creating a flood risk. An international team of scientists warned that if the current melt rates persisted, it was possible that at least 44 glacial lakes in the Himalayas could burst their banks within the next five years.