The dying rivers have spoken

NewAge, May 1, 2009

For Bangladesh, a country that would probably fare the worst in the face of climate change because of raised sea levels, such consequences of glacial retreats in the faraway Himalayas could be disastrous. As large swathes of Bangladesh’s coastal belt are already ravaged by cyclones, salinisation and rising sea-levels, scientists say the decrease in volume of year-round freshwater from Himalayan glaciers could bring disease, drought, and deluge of unseen proportions, writes Mahtab Haider*

THE implications of the study released by the National Centre for Atmospheric Research in the United States this month are ominous for Bangladesh. The study reveals that global warming is drying up some of the biggest river systems across the world faster than was previously thought, and more so for those rivers in highly populated areas, which are drying up at more alarming rates. ‘In the subtropics this [decrease] is devastating, but the continent affected most is Africa,’ said Kevin Trenberth of the atmospheric research centre. ‘The prospects generally are for rainfalls, when they do occur, to be heavier and with greater risk of flooding and with longer dry spells in between, so water management becomes much more difficult.’

According to the UK’s Guardian newspaper, the scientists examined recorded data and computer models of flow in 925 rivers, constituting about 73 per cent of the world’s supply of running water, from 1948 to 2004. ‘It found that climate change had had an impact on about a third of the major rivers. More than twice as many rivers experienced diminished flow as a result of climate change than those that saw a rise in water levels.’

According to the NCAR scientists, the Ganges system is among those showing some of the most significant downward trends in freshwater flow as a result of dams and increased population pressures upstream, but also because higher temperatures are causing higher rates of evaporation, with changing rainfall patterns failing to feed into the river system.

For Bangladesh, India, and the region as a whole, there is no doubt that reduced freshwater flows in the Ganges river system will prove devastating in the long run. The effects will be multifarious, effecting agriculture, nutrition, navigability of the rivers, and most of all allowing swathes of land along the coast to become unfit for habitation as rising seawaters advance further inwards.

Diminishing freshwater flows on the Ganges will likely debilitate predominantly agrarian economies along its banks and may eventually strip the region’s people of the major source of protein in their diets, as a result of a reduction in the quantity of micro-nutrients that debouch into the Bay of Bengal, originating in the Himalayas. Sundarban, on both sides of the border, are after all the richest fish nursery in all of South Asia, largely as a result of the ecology of the Ganges from its headwaters to its watershed.

What’s worse, diminishing freshwater flows across South Asian river systems including the Ganges and the Brahmaputra will be further reinforced, say scientists, as a result of shrinking glaciers. The Himalayas have the largest concentration of glaciers outside the polar caps. During the dry season, when water is in short supply, these glaciers feed eight of Asia’s greatest rivers: to the east, south and west – the Yangtze, Hwang Ho, Salween, Irrawady, Mekong,

Tsangpo/Brahmaputra/Jamuna, Indus, and the many tributaries of the Ganges including the Kosi, Gandaki and Karnali that debouch from the Nepali midhills. The glaciers of the Himalayas as a whole are referred to by scientists as the ‘water towers of Asia’, because they serve as storage that release water throughout the year into the rivers of Asia.

According to a report by the World Wildlife Fund, 67 per cent of the Himalayan glaciers are melting at a startling rate and ‘the major causal factor has been identified as climate change’. The Khumbu Glacier, from where Tenzing Norgay and Edmund Hillary began their historic ascent of Mt Everest, has retreated more than five kilometres since they climbed the mountain in 1953. The 30km Gangotri Glacier in India, near the Badrinath pilgrimage centre, has been receding over the last three decades at more than three times the rate than it had during the previous two centuries. The Rika Samba Glacier in Nepal’s Dhaulagiri region is retreating at 10m per year. Such measurements alarm scientists, who were previously used to gauging glacial retreat in centimetres.

And this is not just happening in Nepal’s mountains. Across the Himalayas, from Tibet in the north to the Karakoram in the west, the glaciers are melting so fast that the WWF fears that a quarter of the ice floes could disappear by 2050. In the climate equilibrium that has evolved over millennia, the glaciers (because of their white colour) reflect back sunlight, keeping the high-altitude peaks within a certain temperature range. As the glaciers start melting and receding as a result of global warming, however, they reveal the darker rock underneath, which in turn absorbs more sunlight and intensifies the melting process. Meanwhile, greenhouse gases trapped in the atmosphere then reflect that heat back onto the earth’s surface, accelerating the process even further.

‘The melting glaciers represent a time-bomb that is ticking away even as we speak,’ cautions Pradeep Mool, a specialist on glaciers at Kathmandu’s International Centre for Integrated Mountain Development. ‘Glaciers melt to form high-altitude lakes, dammed with debris and moraine that characterises the landscape of the Himalayas. But as the water from glacial melt accumulates over the years, these dams which are structurally weak suddenly give way, resulting in what we call glacial lake outburst floods, or GLOFs.’

GLOFS, indeed, are the most obvious results of glacial melt. In 1964, one such GLOF destroyed entire stretches of a highway in China and washed 12 timber trucks more than 70km downstream. A GLOF at Nepal’s Dig Tsho glacier in 1985 destroyed a hydroelectric project near Namche Bazaar, as well as bridges, houses and farmlands worth. The total estimated damage was $4 million. ‘And it isn’t just water that crashes down into the valleys,’ says Mool, holding up a photograph from a 1991 outburst in Nepal that swept away entire villages. ‘You have rocks and other debris that rush downriver at enormous speed.’

Since 1964, Nepal alone has witnessed 13 catastrophic GLOF events. There are over 5000 glacial lakes between Bhutan, Pakistan, India, Nepal and Tibet/China, and scientists regard at least 90 of these lakes to be potentially dangerous. ‘The real problem,’ sighs Mool, ‘is that we don’t even know the extent of the problem, since countries such as India and Pakistan will not share the data and maps of their mountainous regions.’ As the glaciers melt and recede, more glacial lakes are expected and hence more incidence of GLOFS.

‘Contrary to popular perception, this isn’t Nepal’s problem or Pakistan’s problem, but a problem for the entire Subcontinent,’ urges Madan Lal Sreshtha. ‘The melt waters from these retreating glaciers mother the river systems of the Brahmaputra and the Ganga, so if these glaciers eventually disappear, the flow in the rivers will be drastically reduced and almost negligible during the non-monsoon months. Says Shrestha, ‘Glaciers accumulate snow during the South Asian monsoon and it is meltwater from these glaciers that feeds river systems that flow through India and Bangladesh during the dry season until April-May,’ he explains. ‘As the glaciers recede, not only will these rivers flood during the rainy season – with the water that is not frozen and held back by the glaciers – but in the lean seasons, there will also be less and less water in these rivers. Eventually, when the glaciers disappear, there will only be a trickle of water in these great rivers in the winter.’

The decrease in non-monsoon flows would affect the populated plains of South Asia in a thousand different ways. Winter agriculture would suffer, recharge of underground aquifers would be affected thus reducing groundwater reserves, and the use of water for urban and industrial purpose would also be affected, as would water transport, fisheries, wetlands, and water-dependent wildlife. Overall, we are looking at long-lasting impact that that has not even begun to be studied at a time when we are just awakening to the fact of receding glaciers.

For Bangladesh, a country that would probably fare the worst in the face of climate change because of raised sea levels, such consequences of glacial retreats in the faraway Himalayas could be disastrous. As large swathes of Bangladesh’s coastal belt are already ravaged by cyclones, salinisation and rising sea-levels, scientists say the decrease in volume of year-round freshwater from Himalayan glaciers could bring disease, drought, and deluge of unseen proportions.

A model developed in part by the Indian Centre for Ecology and Hydrology reveals that glacial melt will result in ‘an increase in river discharge at the beginning causing widespread flooding in the adjacent areas.’ But after a few decades, the model warns, this situation will reverse and water levels in these rivers will start declining to permanently decreased levels. In the upper Indus, the study shows initial increases of between 14 and 90 percent in flows over the first few decades, followed by flows decreasing between 30 and 90 percent over the following century.

When world leaders meet in December this year to hammer out a long term deal on how to tackle the spectre of climate change, they should be reminded that the fallout of global warming is no longer in the realm of academic projections. People in some of the poorest parts of the world have already started living these realities.



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