Contribution of water from glaciers to Ganges, Brahmaputra and Indus will increase through 2050, then decrease by 2100
As Himalayan glaciers melt due to climate change, water availability in the Ganges, Indus and other river basins in the Hindu Kush region is set to increase in the short term and decrease in the long term, according to a new report from the International Centre for Integrated Mountain Development (ICIMOD).
The contribution of water from glaciers will increase through 2050 and then decrease by 2100, highlighted the Water, Ice, Society, and Ecosystems in the Hindu Kush Himalaya (HI-WISE) report.
“As the glaciers continue to melt and get smaller, the water eventually starts to decrease. We call this point peak water, when the change occurs from increasing glacier runoff to decreasing glacier runoff,” Miriam Jackson, ICIMOD senior cryosphere specialist told Down To Earth.
Jackson is also United Nations’ Intergovernmental Panel on Climate Change’s lead author for the Special Report on the Ocean and Cryosphere in a Changing Climate.
Many areas around the world have passed “peak water” and communities are dealing with less glacier meltwater, HI-WISE said. “For the Hindu Kush Himalaya, we have not reached that point yet, but it is coming soon,” she warned.
In the Hindu Kush region, melting snow and glaciers contribute significantly to river and groundwater flows. Rivers primarily get water from snowmelt in April-June and glacier melt during June-October. They also replenish aquifers.
The Hindu Kush Himalayas have seen a 65 per cent faster loss of glacier mass. The glaciers lost a mass of 0.28 metres of water equivalent per year (m we) between 2010 and 2019, compared to 0.17 m we per year between 2000-2009.
The glaciers act as a savings bank account. As more snow reaches the top, it is stored as ice for decades and centuries, which will be eventually released as meltwater in the dry months.
“It acts like a ‘buffer’ in the hydrological cycle. As glaciers disappear, that buffer is gone, and any money invested (snowfall) is immediately spent at the end of the winter (melt). There is a chance for more floods and a loss of ‘savings’ for the dry years,” Jakob Steiner, Fellow at the Himalayan University Consortium, explained.
A decline in snowfall of 30–50 per cent is predicted to occur in the Indus Basin, 50–60 per cent in the Ganges, and 50-70 per cent in the Brahmaputra between 2070 and 2100 compared to the average snowfall between 1971 and 2000.
As for snow, water runoff from this source has already fallen between 1979 and 2019 and is set to fall further, jeopardising the livelihoods of 129 million farmers in the Indus, Ganges and Brahmaputra basins.
The number of days with snow cover has decreased by five days per decade, according to the report. “There is also earlier snowmelt, and this affects those who are dependent on meltwater from snow coming at the right time for agriculture,” Jackson explained.
In the Brahmaputra River basin especially, the trend in snow cover area since 2002 shows a clear downward trend, she added.
Steiner is concerned that decreasing snow cover could dry up springs, which is bad for agriculture. Plants, he added, are now more directly exposed to the cold weather, when they could hide under a blanket of snow earlier.
About 83 per cent of springs, the main source of water for mountain communities, are replenished through snowmelt and glacier melt. As the snow cover decreases, it will have dire consequences for the 240 million people living in the mountains.
Variations in snow cover make it harder for mountain communities to adapt. Researchers have seen a large positive increase in snow persistence this year across almost all of the Hindu Kush region.
“This makes adaptation even harder, as people (and ecosystems) need to adapt not only to decreasing snow cover and decreasing meltwater from the snow but also to big changes from one year to the next,” Jackson added.
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