Scientists have cautioned that flooding caused by bursting glacial lakes is putting a growing number of people at risk.
Meltwater accumulates and creates lakes as the world warms and glaciers retreat, sometimes as a result of ice or moraine serving as a barrier. The volume, area, and number of these glacial lakes have increased by 50% globally since 1990. When these reservoirs become too full, they risk bursting or overflowing, spilling massive amounts of water and causing catastrophic flooding.
Some lakes are more dangerous than others, and are more likely to trigger glacial lake outburst floods (GLOFs). Professor of climate and environmental change at Exeter University, Stephan Harrison, said:
“The ones we’re concerned about are the very steep mountain valleys in the Andes and in the Himalayas, where you have glaciers retreating up into their steep valleys with lots of opportunity for bits of mountainside to fall off into lakes.”
The connection between rising temperatures and glacial lake outburst floods is not straightforward. Although anthropogenic climate change is to blame for glacial lake creation and development, non-climatic factors such as moraine dam geometry, earthquakes, ice or rock avalanches into the lake, and severe rainfall are also to blame for catastrophic flooding.
Adam Emmer, a geographer at the University of Graz in Austria, said: “You need two conditions to generate a disaster – high magnitude GLOF, and exposed population as well as assets in its path. Population expansion along the potential GLOF paths and lack of building development regulations may be even more important driver of GLOF risk, especially in developing countries.”
The size of the downstream population that could be flooded is one of the factors that makes a glacial lake potentially dangerous, and this number can range from a few hundreds to hundreds of thousands, as in the case of Huaraz, Peru, which is located downstream of Lake Palcacocha. However, due to the many variables at play in an outburst flood, it is difficult to quantify the number of people who might be at risk globally.
According to a 2016 report, at least 1,348 glacial lake outburst floods have been reported worldwide, with 24 percent having some societal effects.
Floods have claimed the lives of over 12,000 people. The most affected area was Central Asia, which was followed by South America, the European Alps, Iceland, Scandinavia, north-west America, and Greenland. The authors describe South America and Central Asia as the regions most likely to see large numbers of deaths, severe infrastructure disruption, farmland flooding, and home and road destruction.
70% of the world’s tropical glaciers are found in the Peruvian Andes, and they are gradually melting, resulting in many glacial disasters in recent decades. The worst so far was the Lake Palcacocha glacial lake outburst flood of 1941, which killed at least 1,800 people.
As a result, as early as the 1950s, Peru began working on lake monitoring and hazard mitigation measures including draining lakes, reinforcing weak moraine dams with concrete foundations and artificial spillways, and constructing early warning systems.
“In reality, the Peruvian Cordillera Blanca [part of the Andes mountain range] is the world’s pioneer area of GLOF mitigation efforts,” Emmer said. Despite this, he added that “the greatest challenge is yet to come – communicating the risk and risk mitigation steps to local communities and gaining their confidence and acceptance.”
After two major floods in the 1980s, Nepal, which is also highly prone to glacial floods, became interested in GLOFs. Nepal drained Tsho Rolpa, a rapidly growing lake near Mount Everest, in 1999 to lower lake levels, a first in the area.
“GLOF has been recognised as a big challenge for Nepal. In the past, there also have been efforts made to reduce the risk from individual lakes and two lakes have already been intervened in [around] the Everest region,” said Arun Shrestha, a climate change specialist at the International Centre for Integrated Mountain Development.
Nepal has recorded records of up to 35 GLOF cases, according to Shrestha, but the true number is likely higher. A study published last year described 47 potentially dangerous glacial lakes that could impact Nepal if breached, but only 21 of them were in Nepal. In addition, twenty-five were found in China and one in India.
“It’s very important that Nepal talks with China and tries to address those issues,” said Shrestha. “Those lakes cannot be ignored, but for that, a bilateral diplomatic effort is required. With climate change, and infrastructure and settlements changing quite rapidly, I think the risk is growing every day.”
Despite the rapid retreat of glaciers around the planet, the frequency of GLOFs has decreased globally. This trend is attributed to a lag between climate change and the occurrence of GLOFs, according to scientists.
GLOFs are expected to rise in the coming decades and continue well into the early twenty-first century, according to scientists. Vulnerable countries with flood-prone populations and infrastructure are racing against the clock to invest in disaster preparedness in order to prevent disastrous consequences in the event of an outburst flood.
Source: The Guardian