Effect of Global Warming

The global climatic change during the first half of the twentieth century has brought a tremendous impact on the high mountainous glacial environment. Many of the big glaciers melted rapidly and gave birth to the origin of a large number of glacier lakes. Due to the faster rate of ice and snow melting, possibly caused by the global warming, the accumulation of water in these lakes has been increasing rapidly and resulting sudden discharge of large volumes of water and debris and causing flooding in the downstream. Glacial lake outburst flood (GLOF) causes disasters to life and property along the downstream, results serious death tolls and destruction of valuable forests, farms and costly mountain infrastructure.

In the Himalayan region, it has been observed that the frequency of the occurrence of GLOF events has been increasing in the second half of the twentieth century. The recent catastrophic GLOF event in the Nepal Himalaya known as the Dig Tsho GLOF in 1985, has destroyed the Namche small hydel project that was built at the cost of US$ 1.5 million approximately. Accurate and timely information on the spatial locations and regular monitoring of the glacier lakes' behavior is needed, to prevent and monitor the GLOF hazards and assess the damages to be occurred in the near future. Modern information tools such as Remote Sensing and GIS could play a lead role in identifying potential risk lakes and monitoring the GLOF events in near real time.

UNEP through its facilities at Environment Assessment Program for Asia-Pacific (EAP.AP), Asian Institute of Technology, Bangkok, is trying to establish an operational early warning system to monitor GLOF hazards in the Hindu Kush Himalayan region. The expected outputs of the proposed study are (i) an inventory of existing glacier lakes along the Hindu Kush Himalaya; (ii) monitoring of potential risk lakes for draining; and (iii) an operational early warning mechanism for GLOF hazards.

Nearly 50 lakes, high in the Himalayas, could burst their banks sending millions of gallons of deadly floodwaters swirling down valleys, putting at risk tens of thousands of lives scientists are warning.

The lakes are rapidly filling with icy water as rising temperatures in the region accelerate the melting of glaciers and snowfields that feed them.

In Nepal, for example, data from 49 monitoring stations reveals a clear increase in temperature since the mid-1970s with highest temperatures found at higher altitudes.

Scientists with the United Nations Environment Programme (UNEP) and the International Centre for Integrated Mountain Development (ICIMOD) have found at least 44 glacial lakes that are filling so rapidly they could burst their banks in as little as five years' time.

Surendra Shrestha, Regional Coordinator in Asia for UNEP's Division of Early Warning and Assessment, said: "Our findings indicate that 20 glacial lakes in Nepal and 24 in Bhutan have become potentially dangerous as a result of climate change. We have evidence that anyone of these could, unless urgent action is taken, burst its banks in five to 10 years time with potentially catastrophic results for people and property hundreds of kilometres downstream. These are the ones we know about. Who knows how many others, elsewhere in the Himalayas and across the world, are in a similar critical state?"

Klaus Toepfer, Executive Director of UNEP, said: "Mountains were once considered indomitable, unchanging and impregnable. But we are learning that they are as vulnerable as the world's oceans, grasslands and forests to environmental threats and insensitive, unfettered, development".

Mountains are the world's water towers feeding the rivers and lakes upon which all life depends. If the glaciers continue to retreat at the rates being seen in places like the Himalayas, then many rivers and freshwater systems could run dry, threatening drinking water supplies as well as fisheries and wildlife. We now have another compelling reason to act to reduce emissions of carbon dioxide and other greenhouse gases," said Mr Toepfer.

In August 1985, a sudden out burst flood from the Dig Tsho glacial lake in Nepal destroyed 14 bridges and $1.5 million worth of damage was caused to the nearly completed Namche Small Hydropower Plant.

Bhutan's Raphstreng Tsho glacial lake in the Pho Chu River sub-basin measured 1.6 km long, 0.96 km wide and was 80 metres deep in 1986. The figures (1995) show the lake has swollen to be1.94 km long, 1.13 km wide and has a depth of 107 metres. Its neighboring glacier could generate a GLOF up to two-and-a-half-times that which caused major devastation in October 1994. The 43 other glacial lakes, pin pointed in the survey and deemed to be in a dangerous state, show similar patterns

The filling of the lakes, and the threat of their mud and debris walls being breached, is as a result of rising temperatures melting the glaciers.

Satellite, mapping and other surveys indicate that, for example, the glaciers in Bhutan are retreating at a rate of 30 to 40 metres a year.

In some areas the retreat is even faster. The Tradkarding glacier, which feeds the Tsho Rolpa glacial lake in Nepal's Rolwaling Valley, is retreating at a rate of over 20 metres a year and, in some years within the last decade, reached 100 metres per year.

The UNEP Regional Resource Centre-Asia and the Pacific, the ICIMOD's Division of Mountain Environment and Natural Resources' Information System, the Department of Geology and Mines of the Royal Government of Bhutan and the Department of Hydrology and Meteorology of His Majesty's Government of Nepal carried out the research.

Effect of Earthquakes

Need to Plan

This years devastating monsoon floods in Bangladesh, Assam and northern Uttar Pradesh reminded the inhabitants of these regions, yet again, about how bad things can get. The disasters were also a warning to others in the Himalayan watershed that even bigger disasters will surely come. To estimate the extent of the casualties and the inadequacy of relief and rescue efforts one only needs to look at some of the great Himalayan events in recent geological time and imagine what would happen if they were to take place today.

A gigantic avalanche and flood came off the Annapurna Range in Nepal about 1,000 years ago and swept down the Seti River depositing debris several hundred feet deep in a valley where the town of Pokhara is now located. A similar avalanche now would kill as many as 100,000 people.

The Tista River that flows down from the Darjeeling hills into Bangladesh to meet up with the Brahmaputra used to flow into the Mahananda and the Ganges in Bihar till 200 years ago. Had that sudden river capture happened today, it would have swept away thousands of villages in a gigantic flash flood.

The nearby Kosi River has "migrated" some 150 km westwards in the past 200 years, and in the next great flood it could easily revert to its earlier riverbed with catastrophic consequences for northern Bihar.

This is the region of the world that combines areas with the highest rainfall in the world, the highest, youngest and most unstable mountain chain, the greatest population density and one of the most extensive levels of poverty. But the science to study this watershed, and the engineering solutions to build rivers, bridges and dams in them are based on inappropriate parameters, false premises and wrong priorities. Rules made for the gentle brooks and placid rivers of more temperate climes are just not applicable for the stupendous sediment loads, precipitation levels, and looming dangers like glacial lake outbursts and seismic damming of rivers.

Take the Kulekhani Dam built in the early 1970s near Kathmandu at a cost of 180 million dollars to generate 90 megawatts of power and have an economic life of 100 years. On the night of 20 July 1993, a severe cloudbuurst in its catchment area unleashed 540 mm of rain in a 24 hour period bringing down an estimated five million cubic metres of silt and boulders into the reservoir. The rain dumped in one night a sediment load several times larger than the estimate made by Kulekhanis designers for the entire lifespan of the dam. It blocked the penstock intake and required another 40 million dollars to design a bypass to extending the dams life by another 30 years-provided there are no more rainfall events like 1993.

Cloudburst like the one that hit Kulekhani happen several times during every monsoon season in different parts of the Himalaya. This year, 406 mm of rain fell in one day in the Butwal area of central Nepal on the same week that another cloudburst triggered landslides in Garhwal that buried several hundred pilgrims bound for Mansarovar. Both caused severe floods in northern Uttar Pradesh.

Although those floods and the ones in Assam were bad, the mother of all floods was the one that hit Bangladesh this year. The Ganges-Brahmaputra delta is at the tailend of the discharge funnel for the basins of two major rivers stretching from the borders of Himachal Pradesh to southern Tibet, the whole of Nepal, Bhutan, Assams eastern rimlands and Meghalaya. It would be surprising if there were no floods in Bangladesh. In fact, floods have been happening there ever since the Himalayas rose and became a raintrap, and the reason Bangladesh exists is because of the silt deposition over millenia during annual floods.

Questions are again being asked: can Bangladesh ever be free of floods? Does it even make sense to try to control them?

In trying to prevent floods, we first need to separate the myths from the truth, and pinpoint the real causes. Complete flood control in the Himalayan watershed is impossible. Even partial control is an exercise that may be geopolitically, financially and (more important) technically problematic at present.

The other side of the story

And the question arises: should we be trying to prevent floods at all? Or should we be looking at what it is we do to when we try to control them that makes floods worse. Is it better to try to live with them, and to minimise the danger to infrastructure while maximising the advantages that annual floods bring to farmers? Plans for long-term flood mitigation efforts need a paradigm shift in the way we think about them, about what is possible and what isnt.

After the 1993 floods on the Bagmati River in Bihar, farmers were interviewed. They said: "Our houses are all gone, but thats all right. We have a bumper crop." Every major flood in Bangladesh has been followed by good winter and spring harvests the following year because of the silt replenishment of farmlands. People of Tangail in Bangladesh looked at the oxbow lake that used to flow by their village as the artery that fertilised the fields every year and brought fish when the flood waters receded. The villagers make a distinction between the beneficial barsha floods and the destructive bona flooding. Traditionally villagers are well prepared for the three months of high water. But ever since levees were built to "protect" Tangail from floods under Bangladeshs ambitious Flood Action Plan, the oxbow is dry, harvests have fallen. "Floods never killed us," they say. "It is flood control that is killing us."

But there are some serious questions being asked about whether we are not putting all our hopes on regional cooperation when there is little proof that even if flood control reservoirs were built in the Himalaya they would be adequate to stop the annual submergence. There are also doubts about the presumption that deforestation in the Himalaya is making the floods worse because of increased soil erosion and siltation. Recent studies show that human activity in the upper catchment of the Himalaya did not have a major effect on floods in Bangladesh and India. In fact, there seemed to be little correlation even between high rainfall in the Himalaya and floods in Bangladesh. It is the rainfall pattern in the Meghalaya Hills directly north of Bangladesh was the main cause of flooding in the delta.

The call to build high dams in the Himalaya is not new, neither is the controversy surrounding it. But the tide of expert opinion is running against dams. First, their cost. The proposed Kosi High Dam at the point where the Kosi breaks into the plains in Nepal will cost anything up to 15 billion dollars, and if it is ever built will be the largest infrastructure project ever conceived in South Asia. Even if the money is found, the kind of negotiations needed for cost-benefit sharing between the governments of Nepal, India and Bangladesh will be extremely convoluted given the political instability and sensitivity to water issues in all three countries.

Gyawali says the problem stems from people who see rivers only as a source of water and devise engineering solution to use and control it. "Rivers are also drainage systems. They have a right to flow out to the sea. When you deny a river that right, it will overflow because it has nowhere else to go."

Geologists and water experts argue that the theory of Himalayan degradation worsening floods has been exaggerated. They say loss of forest cover is not the only reason for flooding, and most of the siltation is caused by natural mass-wasting of the Himalayas due to its steep and geologically young formations. However, if flood control storage is considered, watershed conservation is crucial, says ICIMOD, which looks at the specific environment and development needs of the Hindu Kush-Himalayan region.

Floods have their benefits, and a second school of thought advocates learning to live with floods so that the farmlands can take their benefit, while protecting houses, water supply and roads. Proper town planning, zoning and building design that take the annual flood events into account would be one way. Floods are good for soil, replenishing nutrients

Experts like Dr Rashid believe that if the storage dams have energy and irrigation benefits besides flood control, then they will make economic sense for countries in the region. "The first consideration must be to produce hydroelectricity. Nepal has enough potential to build dams which could produce electricity for the whole of Nepal, Bangladesh, northern India and part of Pakistan," he adds.

"It would be a great help for the flood management if a reservoirs are built in these catchments," says Prof Ainun Nishat of IUCN Bangladesh, especially citing the Kosi proposal and the Tipaimukh and the Dihang-Subanseri projects in India. Studies have identified 26 sites where such water storage could be possible by building dams in Nepal. However, seven large sites were later identified jointly which could serve all these three purposes.

The task force report also recommended that while dredging of rivers in India and Bangladesh for improving flood drainage may not be effective, it would be useful to carry out dredging of offtakes, mouths and man-made channels to improve their conveyance capability. Both Bangladesh and India also agreed that direct point to point flow of information on water level should be transmitted for effective flood management.

In the short-term, though, everyone seems to agree that the best way to avoid casualties would be to have an effective early warning system for floods based on rainfall and river flow data so that downstream inhabitants can take precautions. The Bhutan report said exchange of data and meteorological information of the catchment areas and rivers could improve flood forecasting. The real time water levels and flows of the tributaries from Bhutan namely Magdechu, Mochu, Amochu, Wagchu at their terminal stations, for instance, would be useful for early warning of floods in the Brahmaputra. The data could be transmitted electronically from Bhbutan and Nepal to India and Bangladesh. "Watershed management is a long term vision," says Dr Nishat, "Right now, we should focus on short-term solutions like proper flood forecasting. We should improve flood forecasting by continuously feeding data of major rivers. To do that, we must have cooperation from India and Nepal."

Despite the limitations of regional flood control, and its evidence that floods are more a case of drainage congestion than too much water, there is reluctance to abandon orothodox thinking and the tilt towards engineering solutions. Regional cooperation, however desirable in the long-term, has not moved beyond rhetoric. In that sense, it may be just as well that countries in the region cannot agree. This may at last force them to do their own domestic homework on water management first.

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