A river basin in the Central Himalayas is at risk of dramatic glacial lake outburst floods, which can cause great loss in downstream areas, according to a recent study in the journal Mountain Research and Development.
Glacial lakes form as glaciers melt, and they can burst and cause floods when an ice dam, or an earthen and rock dam formed by a glacial moraine, fails. In recent years, glacial lake outburst floods have received increasing attention. In the face of the threat posed by these floods, the study conducted by Narendra Raj Khanal and two other researchers identified the lakes most at risk of causing floods and proposed that it is necessary to construct monitoring and early-warning systems to warn people of an imminent flood, should one occur.
With global warming, more and more glaciers are melting and the volume of rivers and lakes downstream has increased; the naturally-occurring dams might not be strong enough to hold the extra water. The researchers found that glacial lake outburst floods increased in the Himalayas from 1910 to 2000, albeit insignificantly.
Scientists remain worried about the possible floods from melting glaciers because floods could lead to not only property loss but also the the loss of human life. The records of previous glacial lake outburst floods events demonstrate the danger they have. In 1935, when the Taraco glacial lake burst, wheat fields were submerged and yaks were “swept away,” according to the study. In the 1981 Quxing Village’s flood, a village as well as bridges, homes, and part of a hydroelectric dam were damaged. Furthermore, considering the boom of tourism and international trade in Nepal and China, the cost from floods has dramatically risen. Local people’s lives are under threat too; the study reports that thousands of people live in areas that could be hit by a glacier lake outburst flood, and that millions of dollars of property are at risk.
In order to identify glacial lakes that are at risk of bursting and flooding, the scientists first did some general research on the target area, which was the Poiqu/Bhote Koshi/Sun Koshi, a transboundary river that originates in China and flows into Nepal and India. Using satellite imagery and Google Earth, the scientist found large-volume lakes; they also conducted fieldwork. They eventually identified 10 critical lakes— among them, six they described as “very critical”– that were at the highest risk of flooding and then used equations to specifically estimate the volume of those lakes. Afterwards, they tried to calculate the possible loss if floods were to occur. The scientists finally recommended risk reduction strategies.
A current early-warning system composed of sensors and automatic sirens is located proximate to the Nepal-China Friendship Bridge. However, the scientists found the adopted systems are not effective enough at warning people with enough time, and point out that there’s no system downstream.
As a result, they recommended a better monitoring and an early-warning system. The authors write: “It is recommended that the monitoring systems transmit information by wireless technology in real time to a management center staffed with (or linked to) experts who can judge whether the discharge or water level is abnormally high and indicative of an increased glacial lake outburst floods’ risk.”