With 1,600 glacial lakes, Himachal at flood risk
The glacial lake outburst flood (GLOF) at Joshimath in Uttarakhand has once again put the spotlight on the 1,600 glacial lakes that have formed in Himalayan river basins in Himachal Pradesh and pose a threat to settlements and ecology in case of a rupture.
The formation of these lakes, which vary in size from five to 10 hectares, has been primarily attributed to global warming, climate change and local factors.
SS Randhawa, principal scientific officer at the State Centre on Climate Change, said, “The situation in Himachal Pradesh is no different from that in Uttarakhand. The lakes pose a grave threat to all that lies downstream.”
“Glacial lakes that are over 10 hectares in size pose a greater threat and have to be monitored regularly,” Randhawa said.
2005 lake burst
An artificial lake formed in a geomorphic depression in the course of Parceehu River had burst in 2005 when rapid glacial melting in summers had increased the water level in the river. The lake burst had caused extensive damage along the Sutlej River.
The resulting flood had washed away at least 12 bridges in the Kinnaur-Rampur belt and several villages, including Leo village in Kinnaur. Sutlej’s water level had increased by an unprecedented 25 metres. The damage to government properties was estimated to be around ₹800 crore.
Rapid increase in lakes over last 5 years
Himachal Pradesh Council of Science and Technology monitors lake formation in river basins through remote sensing and satellite data.
Studies have revealed that rapidly melting glaciers have led to the formation of numerous lakes in the basins of perennial Himalayan rivers, including Sutlej, Chenab , Beas and Ravi and their tributaries, over the last five years and that the number of lakes has been increasing at an alarming rate. Data collected between 2015 and 2018 shows that there was a 36% drop in lakes in the Beas basin. However, there has been a 32% increase in lakes in the Chenab basin, 94% increase in the Ravi basin and 97% increase in the Sutlej basin.
Sutlej has most glacial lakes
An analysis of images captured between 2015 to 2018 revealed that the Sutlej basin has 769 lakes, of which 663 are below five hectares, 57 lakes have an aerial range between five to 10 hectare and 49 lakes extend over 10 hectares. An additional 127 lakes have sprung up in the basin since 2017, indicating an overall increase of around 16% lakes in the basin.
In the Chenab basin (Chandra, Bhaga, Miyar), 254 lakes were delineated, of which 64 were in the Chandra sub-basin, 84 in the Bhaga sub-basin and 106 in the Miyar sub-basin.
The Chenab basin had 192 lakes in 2015. However, the count had increased to 254 in 2018. Notably, only 55 lakes had been reported in the Chenab basin in 2001.
Aerial measurements indicate that 240 lakes are less than five hectares, 10 between five to 10 hectares and four extend over 10 hectares, which indicates a 20% reduction in bigger lakes.
35% decrease in Parvati sub-basin
There was a 35% decrease in lakes in the Parvati sub-basin in 2018 in comparison to 2017. Scientists attribute this anomaly to the high cloud cover in the Jiwa basin.
Of the 65 lakes in the sub-basin, 58 lakes were small, with an area below five hectares, four lakes had an aerial range between five and 10 hectares and three lakes had an area of more than 10 hectares in 2018, indicating an overall reduction of around 36% for small lakes and a drop of 25% in case of bigger lakes since 2017. No change was apparent in lakes with an area between five to 10 hectares.
In the Ravi basin, 66 lakes were documented in 2018, while only 54 had been mapped in 2017. Studies indicate three lakes were over 10 hectares, two lakes were between five to 10 hectares and 61 lakes were spread over less than five hectares.
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