[Science Scope] The Paradox of a Melting Himalayas: Overflowing Waters Begin to Dwindle

As Glaciers Melt, Flood Risks Rise—But ‘Peak Water’ Looms

The Himalayas: Asia’s “Water Tower” at Risk—Threatening Drinking Water, Agriculture, and Hydropower

Editor's Note'Science Scope' is a feature series that takes an in-depth look at specific phenomena in science and technology, analyzing their significance and future implications.

The glacier of Langtang Lirung in the Nepal Himalayas extends from the mountain summit down to the valley below. High-altitude glaciers act as "natural reservoirs" by storing snow and ice and melting during the warmer seasons to supply water to rivers. Photo by Maysam Yabandeh/Pixnio

On August 26, a massive mass of ice and rock collapsed in the Himalayas.

In the highlands of Langtang National Park, north of Kathmandu, Nepal, part of a glacier and bedrock broke off and tumbled down into the valley below. The impact was so powerful that it was initially mistaken for an earthquake. According to the U.S. Geological Survey (USGS), the strong tremors captured by seismographs at the time were signals generated by the enormous ice and rock falling into the valley, rather than an actual earthquake.

This collapse was the beginning of a chain disaster. The flow, a mix of ice, rocks, water, and sediment, surged downstream, sweeping away villages, roads, and bridges. Some analyses found that, in just 30 minutes, water levels in parts of the downstream Trishuli River had risen by 9 meters. As of September 8, at least 11 hydropower projects had been damaged.

The bigger changes unfolding in the Himalayas don’t end with a single collapse. As the planet warms, glaciers are melting rapidly. Initially, the more ice melts, the greater the volume of water flowing into rivers. However, as glaciers continue to shrink, a tipping point is reached. The volume of ice stored high on the mountains declines, leaving less water to flow into rivers.

The increase in water from melting glaciers is not permanent. Eventually, it begins to dwindle.

The 'Natural Reservoirs' on the Mountains Are Disappearing

High-altitude glaciers store snow as ice during cold seasons and then gradually release meltwater to rivers as temperatures rise. They serve as massive natural reservoirs.

Jinho Ahn, Director of the Cryospheric Science Education and Research Center at the Institute for Future Innovation, Seoul National University, and Professor of Earth and Environmental Sciences, explained, “High-altitude glaciers play a crucial role by storing water in solid form and continuously supplying meltwater. If glaciers and snowpacks decrease rapidly and largely disappear, it could cause not only an increased risk of floods, but also severe problems in securing drinking and agricultural water.”

AI-generated image.

According to the “2025 State of the Climate in Asia” report from the World Meteorological Organization (WMO), all 23 glaciers monitored in High Mountain Asia lost mass between October 2024 and September 2025. The WMO stated that glacier retreat in this region has continued for decades, with the pace accelerating further since the mid-1990s.

High Mountain Asia, centered on the Tibetan Plateau, contains the world’s largest reserves of ice outside the polar regions. The Hindu Kush Himalaya stretches about 3,500 kilometers from Afghanistan to Myanmar, serving as the source for 10 major rivers, including the Indus, Ganges, Brahmaputra, Mekong, and Yangtze. The International Centre for Integrated Mountain Development (ICIMOD) notes that about 2 billion people depend on water originating from this region.

Kyung Jin, Policy Cooperation Director at the Korea Polar Research Institute, said, “Changes in high-altitude glaciers go beyond the simple loss of ice. There is a need to look at these changes in terms of ‘cascading effects,’ where risks originating from mountainous regions travel downstream along rivers to impact populations and infrastructure.”

Melting Glaciers Fuel Chain Disasters

Glacier melt does not automatically trigger devastating floods. Even for the recent disaster in Nepal, pinpointing climate change as the direct cause requires precise attribution analysis.

However, as warming accelerates environmental changes in high-altitude regions, new risks are rapidly emerging. As glaciers retreat, glacial lakes may form where ice once existed, or existing lakes may expand. If an ice avalanche or landslide falls into a glacial lake and natural moraine dams break, an immense volume of water can be suddenly released in what is known as a Glacial Lake Outburst Flood (GLOF).

ICIMOD’s survey of major river basins in the Hindu Kush Himalaya confirmed the existence of 25,614 glacial lakes in the region.

AI-generated image.

This recent disaster in Nepal differed from a typical GLOF. Initial satellite imagery and seismic analyses suggest that both glacier and bedrock collapsed in a highland area, sending massive amounts of ice and rock into the valley. Afterward, as more water and sediment joined the flow, it was amplified into a large-scale flood.

Director Jin emphasized, “It is premature to attribute this disaster directly to climate change without precise cause identification and attribution analysis.” That is, the interplay among glacier retreat, thawing permafrost, collapsing bedrock, expanding glacial lakes, and intense rainfall must all be considered, as each change may trigger new risks.

The Water Increases—Until It Doesn’t

The paradox starts here. As temperatures rise and glaciers melt rapidly, river flows initially increase. This is because even water long stored as ice ends up flowing into rivers.

In a study analyzing the headwaters of five major rivers in High Mountain Asia—the Indus, Ganges, Brahmaputra, Salween, and Mekong—overall river volume for 2041–2050 is projected to rise compared with 1998–2007, due to both increased glacier melt and changes in precipitation. However, the degree and reasons for change differ by basin, depending on the relative dependence on glacial melt, monsoons, and precipitation patterns.

AI-generated image.

But ice is not infinite. As glaciers shrink, the volume of ice available to melt also diminishes. Eventually, after reaching a maximum, the volume of meltwater supplied to rivers begins to drop. Scientists refer to this point as “peak water.”

It’s similar to drawing down bank savings: Initially, withdrawing principal increases your disposable funds, but continuous withdrawals eventually leave you with nothing left to take out. Likewise, after passing “peak water,” glaciers progressively lose their ability to supply rivers during dry periods.

In the early stages of temperature rise, rapid glacier melt leads to a temporary increase in river flows. Yet if glaciers keep shrinking, after “peak water,” the supply of meltwater inevitably tapers off. This is the paradox of glacier loss: at first providing more water, but eventually leading to less.

The Real Problem: Not Just Quantity, But Timing

The shockwaves from changes beginning in the mountains can reach plains and cities thousands of kilometers away.

According to UNESCO’s “World Water Development Report 2025,” 55–60% of the world’s annual freshwater flows originate in mountainous regions, and about 2 billion people depend on these mountain water resources. Mountains store water as snow and ice, then release it during the warmer seasons to sustain drinking water, agriculture, energy, and industry.

However, not all river basins rely equally on glacier melt. The Indus River is highly influenced by snow and glacier meltwater, whereas the Ganges and Brahmaputra are also greatly affected by summer monsoons. Consequently, what matters most is not just the annual total amount of water, but when that water is available.

If river flows drop during the critical growing season for crops, agriculture suffers—even with adequate annual rainfall. Conversely, if heavy rain and meltwater peak together in a short span, excess water cannot be stored and instead causes flooding. In other words, climate change is altering not only the supply of water, but also its “calendar.”

Hydropower is not immune to these changes. Although increased river flows from glacier melt may seem beneficial for generation, mountain floods bring not only water but also rocks, sand, and mud. These debris flows can clog intake valves, damage turbines, and destroy dams, roads, and transmission lines. In the recent Nepal flood, at least 11 hydropower projects were affected.

Over the long term, the opposite risk emerges. As glacier meltwater supplies decline after “peak water,” electricity generation during dry seasons may also decrease. Hydropower thus now faces the dual risks of “too much water” in the short term and “too little water” over the long term.

Water Crosses Borders—So Must the Warnings

Rivers that begin in the Himalayas flow across national borders. Glacier collapse or floods that occur upstream can quickly cross boundaries downstream as well.

Geoff Da Costa, a researcher at the University of Reading in the UK, pointed out, “Early warning for transboundary rivers hinges on international cooperation. The monitoring may occur in one country, but those at risk could be in another.”

Along with international coordination, there is also a need to strengthen observation systems in hard-to-reach mountain areas themselves. Myungki Choi, professor at the Korea Industrial Expertise Corps, said, “The five stages of prediction, prevention, monitoring, warning, and evacuation must be unified into a single integrated system,” emphasizing the use of satellites, drones, and ground sensors together.

It’s not just the ice that is disappearing from the Himalayas. The huge, natural water reservoir system—which stored snow and ice for thousands of years and released water seasonally—is itself transforming.

For now, melting ice increases water volumes, sometimes leading to floods that inundate the lower slopes. But once glaciers have receded past “peak water,” the situation reverses.

The formerly abundant water starts to decline. The greater challenge Asia may face after the glaciers disappear may not be the image of snowless mountains, but the reality that water will no longer arrive when it is needed most.

This content was produced with the assistance of AI translation services.