The glacier model used by the team studied the impact of GhGs on temperatures, snowfall and rain in the region, considered to be the highest in the world.
Published in The Cryosphere on 27 May, the study is among the first to use a distributed (or gridded) approach to model glacier mass balance and redistribution in the Everest region.
“Every day, for every grid cell in the model, we calculate the mass gained (through snowfall) and lost (through melt), which gives the mass balance,” Joseph Shea, glacier hydrologist at the International Centre for Integrated Mountain Development (ICIMOD), Kathmandu, and leader of the study, tells SciDev.Net.
“Our results indicate that the rate of area change (and mass loss) of Nepal’s glaciers between 1990 and 2010 will likely continue in the future,” Shea says.
An ICIMOD study published last May said that Nepal’s glaciers had lost a quarter of their area over the last three decades.
Shea’s team studied glaciers in the Dudh Kosi basin in Nepal, which is home to some of the world’s highest mountain peaks, including Mt. Everest, and has over 400 square kilometres of glacier area. “Glaciers in the Dudh Kosi basin contribute meltwater to the Kosi River, and glacier changes will affect river flows downstream,” says Shea.
The Himalayas contain the largest volume of snow and ice outside the polar regions. Nearly one billion people living downstream in China, India, Pakistan and Southeast Asia depend on the Himalayas and the Tibetan plateau for water.
To find out how glaciers in the region will evolve in the future, the team started by using field observations and data from local weather stations to calibrate and test glacier change over the past 50 years.
Shea says the model took into account monsoon patterns for the historical record, but is unclear about future changes. The findings indicate that increases in precipitation is not enough to offset the increased melt, and part of the glacier response is due to changes in the freezing level.
“The freezing level currently varies between 3,200 metres in January and 5,500 metres in August. Based on historical temperature measurements and projected warming to the year 2100, this could increase by 800—1200 metres,” says study co-author Walter Immerzeel of Utrecht University, the Netherlands. “Such an increase would not only reduce snow accumulation over the glaciers but would also expose over 90 per cent of the current glacierised area to melting in the warmer months.”
However, the researchers caution that the study missed important information about high-altitude meteorology. The initial thickness conditions used to test the model and glacier sensitivity to future climate change are unknown, they admit.
Glacier melt in the Himalayas is a contentious subject. The UN Intergovernmental Panel on Climate Change (IPCC) in its fourth assessment report declared that the glaciers of the Himalayas could disappear by 2035 only to admit later that the projection was an error.
“We need more measurements, both ground and satellite-based, to better understand how much do glaciers in the Dudh Koshi contribute to stream flows in each month, how will this change as the glaciers retreat, and how does this affect flows as you move downstream?” says Shea.
Local experts also stress that global warming is already showing visible impact in the Himalayas but more field and satellite-based studies are needed to pinpoint changes.
“Past data show that temperatures have been rising steadily in the last three decades and glacial lakes, and melt pools in the Everest regions have also expanded rapidly,” says Rishi Ram Sharma, chief of Nepal’s department of hydrology and meteorology. “If GhG emissions continue in business as usual fashion there will definitely be more glaciers melting in the Himalayas.”
>Link to abstract in The Cryosphere
This article has been produced by SciDev.Net's South Asia desk.