A new report has warned that even if global warming is held at 1.5℃, we will still lose a third of the glaciers in the Hindu Kush-Himalaya (HKH) region. What does that mean for rivers that flow down these mountains, and the people who depend on them?
The HKH region is home to the tallest mountains on Earth, and also to the source of rivers that sustain close to 2 billion people. These rivers supply agriculture with water and with sediments that fertilise soils in valleys and the floodplain.
Some of these rivers are hugely culturally significant. The Ganges (or Ganga), for instance, which flows for more than 2,525 km from the western Himalayas into the Bay of Bengal, is personified in Hinduism as the goddess Gaṅgā.
Before we get to the effect of melting glaciers on Himalayan rivers, we need to understand where they get their water.
For much of Himalayas, rain falls mostly during the monsoon active between June and September. The monsoon brings heavy rain and often causes devastating floods, such as in northern India in 2013, which forced the evacuation of more than 110,000 people.
But the summer monsoon is not the only culprit for devastating floods. Landslides can dam the river, and when this dam bursts it can cause dramatic, unpredictable flooding. Some of those events have been linked to folk stories of floods in many cultures around the world. In the Himalayas, a study tracking the 1,000-year history of large floods showed that heavy rainfall and landslide-dam burst are the main causes.
When they melt, glaciers can also create natural dams, which can then burst and send floods down the valley. In this way, the newly forecast melting poses an acute threat.
The potential problem is worsened still further by the Intergovernmental Panel on Climate Change’s prediction that the frequency of extreme rainfall events will also increase.