Lunana experienced the highest temperature in the last nine years last month. This is according to temperature data analysis by the National Centre for Hydrology and Meteorology (NCHM).
Lunana in north recorded its temperature around 15 degree celsius last month, an increase of 2 degree Celsius compared to past years. This the centre say might be the major reason for the incident in Lunana last month.
Following the threat from Thorthormi lake last month, the NCHM conducted rapid assessment findings on the lake. The centre found there has been a consistent rise of temperature in the past months in the area. In the last nine years, the temperature has never increased from 13 degree celsius. This, the officials say is a significant increase.
There are two subsidiary lakes below Thorthormi lake. Before the incident in June, there was one outlet from where the water from the main lake flowed to subsidiary lake I. During the flood, there was a small new breach on the right side of the original outlet channel of the main lake. On breaching, that excess water spilled over into the subsidiary lake I which is located right below the main lake. And from that subsidiary lake, it spilled over to subsidiary lake II. Since the moraine dam of subsidiary lake II is just 40 metres thick which is too thin to hold the water pressure, it gave way.
He, however, said that the breaching of the lake is not a Glacier Lake Outburst Flood or GLOF.
“If you estimate the volume that went out on the 20th June, it’s just about 18000 cubic metres. That’s why we didn’t feel any impact on the downstream regions. The breaching of the small lake along with the new breach that occurred on the main Thorthormi lake, we don’t consider it as GLOF because by terminology GLOF should be a sudden release of a huge volume of water and that didn’t happen,” said Karma Toeb, a Specialist at NCHM.
He explained that the flood volume from 1994 GLOF from Luggye tsho was 18 million cubic metres of water.
The centre plans to enhance the GLOF early warning system that can forecast floods. For now, the centre has GLOF early warning system that detects flood only after it has happened.
Today Lunana has four major lakes, Thorthormi, Rapstreng, Luggye and Baytsho and all the four fall under potentially dangerous glacial lakes. He added that going by the incident earlier, the risk has reduced for now. The centre, however, says they can’t claim it to be GLOF hazard-free.
