New Delhi: Nearly a billion people who depend on the Indus, Ganga and Brahmaputra river basins for life and livelihood are threatened by the impact of global warming in the Himalaya-Karakoram mountains. Melting snow and glaciers will swell the rivers, but changed seasonality will affect farming, other livelihoods and the hydropower sector, while causing floods downstream, a new multinational study by researchers in Indore, Roorkee, Delhi, Bengaluru, Ahmedabad and Nepal, among others, has found.

In India, the Union territories of Jammu and Kashmir and Ladakh, the states of Himachal Pradesh and Punjab and parts of northern Haryana and Rajasthan lie within the Indus River basin. Uttarakhand, Delhi, the rest of Haryana, Uttar Pradesh, Bihar, Jharkhand, West Bengal and large parts of Rajasthan and Madhya Pradesh lie in the Ganga basin. Sikkim and Arunachal Pradesh, and most of Assam, Meghalaya and Nagaland lie within the Brahmaputra basin. The affected persons, including in the megacities of Delhi, Lahore, Karachi, Kolkata and Dhaka, amount to nearly 13% of the global population in 2021, or one in eight people.

The basic runoff of rivers (the water flowing into rivers) in the Himalaya-Karakoram (HK) region comprises snow melt, glacier melt, rainfall and base flow from groundwater, per the study. Half the ice in the HK region is held in glaciers. The rate at which, and when, these glaciers melt affects the flow of river water in different seasons. Usually, the rivers carry snow melt from the HK mountains in summer, from April to June, then glacier melt to October, before winter hardens the snow and ice again.

Global heating, which is affecting glaciers, snowfall as well as rainfall patterns in the HK region, will have downstream consequences on the river basins. The study projects that there will be an increase in glacier melt, total river runoff and flows during different seasons until the 2050s.

The HK river basins cover an area of 2.75 million sq km, have an irrigated area of 577,000 sq km and an installed hydropower capacity of 26,432 MW, according to the study. The potential changes in river runoff will impact the timing and volume of meltwater available for irrigation, which is critical during the spring planting season, and for reliable hydroelectric power generation during the pre-monsoon period, said the study.

"When we have more meltwater in the future due to intense [glacier] melting and increase in monsoonal rains, we will have more water in rivers. At the same time, glaciers are melting earlier in the summer. Instead of June, they are melting in April. That means the seasonality of meltwater is changing. This shifting in seasonality of meltwater will affect livelihoods and the economy," Mohd. Farooq Azam, lead author of the research and assistant professor at Indian Institute of Technology, Indore, told IndiaSpend.

The Karakoram anomaly

Changes in local, regional and global climate patterns due to global heating will have varying impacts on glaciers in the HK region, per the study. While river runoff in the Indus basin depends more on glacier meltwater and snow melt, the Ganga and Brahmaputra basins depend more on monsoon rainfall, Azam explained. Thus, earlier melting of glaciers means more adverse impact for people living in the Indus basin.

The estimated contribution of ice and snow melt in the total Indus river runoff ranges between 21-40% and 22-49%, with estimates varying owing to different methodologies, modelling and the time period considered for each study, past research has shown. In contrast, in the upper Ganga basin, combined snow and ice melt accounted for 20% of total runoff while rainfall and groundwater contributed 66% and 14%, respectively, according to this study.

Glacial melt is already changing water regimes of the Himalayan rivers and some of the immediate effects are seen in terms of drying up of springs, which are the main source of drinking water for people in the mountains, climate scientist Anjal Prakash said. The increased runoffs would contribute to flooding downstream and affect lives and livelihoods. Prakash is a research director and adjunct professor at Bharti Institute of Public Policy, Indian School of Business in Hyderabad and a coordinating lead author for the Intergovernmental Panel on Climate Change Special Report on the Ocean and Cryosphere in a Changing Climate, published in 2018.

"The mountain communities and people living downstream are more prone to climate risks and the incidence of such climate-related disasters has been increasing in the region in the past two decades. These would greatly affect the people as Hindu Kush-Himalayas is one of the most densely populated and poverty-stricken mountain regions of the world and any small climate changes will affect a large proportion of people," Prakash told IndiaSpend.

The varied impacts of warming across glaciers are illustrated well through the 'Karakoram anomaly', a term used by the scientific community to refer to the trend of stable or growing glaciers in the Karakoram mountain range, as opposed to retreating glaciers in Himalayas, in the face of climate change.

The shrinking or growth of glaciers is termed the mass balance of glaciers, which denotes the sum of snow accumulation and loss of snow and ice during summer. When accumulation exceeds loss, it is referred to as positive mass balance.

"Compared to other parts of the Himalayas, the Karakoram is showing positive mass balance and therefore, it is anomalous. Some say, it is because of peculiar atmospheric conditions, higher snowfall or temperatures. Its glaciated terrain is also at higher altitude," said Anil Kulkarni, co-author and distinguished visiting scientist, Divecha Centre for Climate Change, Bengaluru.

Jeffrey Kargel, a co-author of the study and a senior scientist at the Planetary Science Institute in Tucson, Arizona, explained that the impact of climate change on glaciers is complex in so far as the HK region is concerned. Kargel said that the climate is warming at different rates in different parts of the Himalayas, and summer temperatures in the Karakoram, for instance, are stable or maybe decreasing in some valleys due to the effect of increased cloud cover, which in turn adds an influx of moisture.

"These parts of the Karakoram are among a very few places in the world where this (positive mass balance of glaciers) is happening. But overall, temperatures are rising rapidly. Part of this is due to increasing greenhouse gases, as in other parts of the world, but part of the temperature rise is due to sunlight absorption in the pollution 'brown cloud'. Air pollution has another very big effect, but in detail climatologists do not agree on what is happening specifically," said Kargel.

Kargel, meanwhile, explained that the near-term increase in meltwater from glaciers is akin to a bank account that has an increase of cash flow in the short term but one which will run dry in the longer run. "The water they have stored in the form of ice can produce a big increase in water supplies in the short term as climate warms, but the long term is made more precarious, because eventually the "bank account" of ice runs dry. It is something that water managers need to consider," added Kargel.

Research gaps and preparing for changes in runoff

The findings of the multinational study are also based on a review of major studies on the region, with the aim of highlighting issues concerning glaciers and climate change in the HK region and its impact on hydrology, as well as identifying research gaps in glaciology and hydrology. With millions dependent on the three river basins, the authors say these gaps in research on the effect of warming on glaciers in this region need to be plugged.

"Precipitation is a key factor we need to study. It varies from valley to valley and currently, information on precipitation is largely available from lower altitudes at around 1,000 m elevation. The HK region has a high variability in topography with different precipitation regimes. This is not captured well in models," said Azam.

Expanding observation networks at higher altitudes; establishing fully automatic weather stations at higher altitudes to monitor temperatures and rainfall; and developing projects to study glacier area and volume were some of the recommendations made in the paper. It also suggested a multinational collaboration equivalent to NASA's (National Aeronautics and Space Administration) polar-oriented Icebridge mission which involves airborne survey of the polar ice.

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