High-altitude flood warning
|Feb 4, 2008|
Glacial lakes in the Bhutan-Himalaya
The upper Himalaya lakes in Nepal and Bhutan that were formed by retreating glaciers are getting bigger as global warming causes glaciers to recede, with possibly ruinous consequences, a development that Japanese scientists have been monitoring with concern.
It is not a new phenomenon, but it is a growing and dangerous one. The International Center for Integrated Mountain Development in Katmandu estimates that 15 glacial lakes have burst in recent years, an average of one every two to five years. The center figures another 20 or so are candidates for Glacial Lake Outburst Flooding, or Glof.
In 1985, for instance, a natural earthen dam that was holding back the waters of Dig Tsho Lake near Mt Everest suddenly gave way. In four hours the entire lake, about 10 million cubic meters of water, gushed out, drowning a hydro dam and washing away scores of bridges and roads downstream.
The one that generating the most interest now is Tsho Rolpa, northeast of Katmandu. A mere pond 50 years ago, the lake is up to 3.5 kilometers long and 500 meters wide, according to the last survey.
The Nepalese Ministry of Environment, Science and Technology estimates that if the moraine holding back the water were to burst, it would release something like 100 million cubic meters of water. Within minutes the flood would engulf a village 10 kilometers downstream where Nepalese tend yaks and sheep.
The phenomenon has attracted the attention and concern of scientists at Nagoya University in Japan, who have been surveying Nepal’s glaciers in cooperation with the Nepalese government. Their latest mission took place late last year. The main purpose of that mission, says Koji Fujita, associate professor of glaciology, was to establish a basis for satellite mapping.
This recognizes that traditional survey methods such as aerial surveys or ground mapping are not up to the task. There are simply too many lakes – some 2,323 to be exact – and more than 3,000 glaciers to keep track of. And with the warming climate, the lakes are constantly growing.
This time, given global warming’s higher profile as a public concern, the Asahi Shimbun sent a reporting team and an aerial surveillance aircraft to Nepal along with the scientists. The team flew to northeast Nepal to view lakes close to Mt Everest.
They found, among other things, that Inja Tsho Lake, not far from Everest, had expanded to about 2 kilometers in length and 600 meters in width since 2002 when the Nagoya University team last surveyed it.
The reporters also met with Nepal’s Prime Minister Prasad Koirala, who urged Japan to do more to help prevent flooding in the Himalaya by forming a joint lake outburst flooding institute with Nepal.
Draining lakes as they expand is one obvious though expensive and uncertain solution. With funds from the World Bank, the Nepalese government began a difficult draining of Tsho Rolpa Lake, but they succeeded in lowering the lake level by only three meters. “This is not enough to prevent glacial lake outburst flooding,” Fujita told Asia Sentinel.
Another solution would be a warning system, sort of like that is used for tsunamis. The trouble is that the triggering events are unpredictable and the consequences develop rapidly. The Dig Tsho flood was triggered by an avalanche that created a tidal wave that overpowered the moraine, causing the dam to burst.
Such efforts have also been hampered by Nepal’s deadly communist insurgency. In the 1990s Nagoya University teams visited Nepal on average twice a year, but the visits diminished during the early 2000s, before a truce with the government was negotiated.
Japanese reporters who walked along the river originating from Tsho Rolpa said that all of the solar panels that the government had installed to power warning devices were gone. “Local people said that the communists took them; others said that the locals did,” Fujita said.
Just how much the growth of glacial lakes in Nepal is a direct consequence of global warming is difficult to say with precision, Fujita noted cautiously. Many lakes began expanding in the 1950s, before global warming was on the radar screen.
Accurate instruments to monitor temperatures at higher elevations (3,000 meters plus) have only been in place for the past 10 years. The Chinese have had weather monitoring stations on the Tibetan Plateau for far longer, and they report a general warming trend. The consensus seems to be that temperatures are rising about six tenths of one percent of a degree of Centigrade per decade.
Fujita pointed out that the problem in the Himalayas is exacerbated by local weather patterns. It makes a difference, he points out, whether precipitation falls on glaciers as rain or snow. A covering of snow tends to reflect sunlight and inhibit melting in winter while restoring some of the bulk lost to summer melting.
The glaciers in Alaska and Greenland, though receding, benefit from a more normal winter-summer cycle of snow and rain. In Nepal the Indian monsoon reigns, bringing more rain and less snow, especially as temperatures rise. "That's why the Himalayan glaciers are so sensitive to global warming,” Fujita said.
While not mentioning the flooding problem directly, Prime Minister Yasuo Fukuda made global warming the subject of his speech in late January to the World Economic Forum in Davos, Switzerland. He plans to make it the centerpiece at the G8 summit this summer, which Japan is hosting in Hokkaido.
He set forth an initiative to curb greenhouse emissions including country-by-country carbon dioxide emission reductions. He also proposed that Japan provide $10 billion in financial assistance to help developing countries, namely China and India, to promote emission curtailment in a way that is compatible with economic growth.