The Himalaya-Karakoram region in South Asia is often called the water tower of Asia or the Third Pole. It is one of the most heavily glacierized mountain regions on Earth. Understanding the response of Himalaya-Karakoram rivers to climate change is crucial for almost 1 billion people who partly depend on these water resources.
Snow and glaciers are melting rapidly in the Himalayan range due to climate change, altering water supplies in the rivers like Indus, Ganga and Brahmaputra in the Himalaya-Karakoram (HK) ranges.
Climate change is causing mountain snow to melt more rapidly and glaciers to shrink, but this is making a widely varied impact on water supplies in Asia, as per a new paper Glacio-hydrology of the Himalaya-Karakoram published in the journal Science.
Himalayan and Karakoram mountain glaciers are the main story with part of the region's annual water supplies, particularly that in very high elevation mountain valleys and villages near the glaciers. At more distant points, elevations are lower and glaciers have a reduced importance as a source of annual water supplies compared to rainfall and melting mountain snow.
However, in some of the lower valleys during the driest seasons in the drier parts of the region, glacier outflows are still dominant, and people's livelihoods and ability to live there depend on glaciers. This affects millions of people.
The research team's work builds a stronger consensus about the important roles of glaciers in regulating river flows in the region and how the shifting climate is affecting those flows. Important gaps in knowledge remain wide and must be filled in coming years.
Few of the gap questions are: "How does snowfall and glacier health vary between river valleys? How thick are the glaciers and how long will they survive in an era of accelerated melting? Why are some glaciers advancing even when most of them are shrinking? The geographic variations in glacier health are substantial, and this means that one size does not fit all when projecting the future changes."
Climate change, however, is not only melting glaciers but is having a broad and deep impact on the overall hydrology from the mountains down to the river deltas. Climate change is altering rainfall amounts and distribution. Changes in the runoff pattern from both rain and glacier melting is expected to increase incidents of extreme runoff and resultant flash floods, landslides, and debris flows.
The projected trends in river runoff volume and seasonality over the 21st century are consistent across a range of climate change scenarios. The total river runoff, glacier melt, and seasonality of flow are projected to increase until the 2050s, and then decrease, with some exceptions and large uncertainties, according to the study undertaken at the Indian Institute of Technology, Indore.
The new work is the most thorough review ever of the region's glacier-fed rivers. The research team led by Dr Mohd. Farooq Azam, assistant professor at the Indian Institute of Technology, Indore gathered the results of nearly 250 scholarly papers to arrive at a more accurate understanding of the links between climatic warming, precipitation change, glacier shrinkage and river flow.
At the region-wide scale, the total impact on each year’s water supply varies. The study shows that glacier, meltwater, and climate change impacts on glaciers are important components of Himalaya-Karakoram rivers with greater hydrological importance for the Indus than Ganga and Brahmaputra basins. This is because the Indus basin is predominantly fed by monsoon rains and are affected mainly due to the changing rainfall patterns. The really big climate change story there is how it affects the monsoons.
The Himalayan river basins cover an area of 2.75 million km2 and have the largest irrigated area of 577,000 km2, and the world’s largest installed hydropower capacity of 26,432 MW. The melting glaciers meets the water requirements of more than a billion people of the region who will be affected when much of the glacier ice mass melts throughout this century and gradually stops supplying the required amount of water.
The work supported by INSPIRE Faculty fellowship funded by the Department of Science and Technology (DST), GoI identified gaps in understanding the impacts of climate change on the Himalayan water resources, and highlighted prospective solutions to bridge these gaps. This INSPIRE Faculty project also resulted in a research documentary earlier.
Policymakers need to assess the current status and potential future changes of rivers for sustainable water resource management for agriculture, hydropower, drinking, sanitation, and hazard situations.
The authors recommend a tiered approach to address the identified gaps: Tier-1 includes an expanded observation network that places fully automatic weather stations on selected glaciers. They also suggest developing comparison projects to examine glacier area and volumes, glacier dynamics, permafrost thaw, and snow and ice sublimation. Meanwhile, Tier-2 recommendations implement the knowledge of these studies in detailed models of glacier hydrology to reduce the uncertainty in projections of future change.
It identified gaps in understanding the impacts of climate change on the Himalayan water resources, and highlighted prospective solutions to bridge these gaps.
To address these gaps, the authors have recommended an expanded observation network that places fully automatic weather stations on selected glaciers along with developing comparison projects to examine glacier area and volumes, glacier dynamics, permafrost thaw, and snow and ice sublimation.
Some aspects of global warming like the impacts on snow, glaciers, and water supplies are in the hands of the region's people and their leaders. Asia now dominates the world's greenhouse gas emissions. Furthermore, smog and soot are thought to be almost as important in causing accelerated melting of Himalayan glaciers as greenhouse gas-driven global warming, according to other studies. If the regional economies could control air pollution, this could bring that part of the glacier shrinkage problem under control. This is a topic of ongoing scientific study by the scientific community.
The full paper can be viewed here