Gangotri glacier melting, rainfall surging: How will this reshape millions of lives downstream?

A new study has reconstructed four decades of water discharge from the Gangotri Glacier System (GGS) in Uttarakhand, offering a rare long-term view of how snow and ice melt are reshaping the Bhagirathi river's flow in the central Himalayas. The findings, reported by The Hindu, highlight how warming temperatures and shifting precipitation patterns are altering one of the most crucial glacier-fed systems in the upper Ganga basin.

The research, titled Hydrological Contributions of Snow and Glacier Melt from the Gangotri Glacier System and Their Climatic Controls Since 1980, was carried out by scientists from the Indian Institute of Technology, Indore, the University of Utah, the University of Dayton and the International Centre for Integrated Mountain Development. The paper has been published in the Journal of the Indian Society of Remote Sensing.

The GGS, which includes the Gangotri, Chaturangi, Raktavaran and Meru glaciers, covers about 549 sq km, nearly half of which is glacierised. It is a vital source of meltwater for the Bhagirathi, which ultimately feeds the Ganga. As The Hindu notes, this smaller catchment is particularly suitable for discharge analysis, since it allows scientists to separate contributions from snowmelt, glacier melt, rainfall and groundwater flow with greater precision compared to much larger river basins such as the Indus or Brahmaputra.

Using a high-resolution hydrological model known as SPHY (Spatial Processes in Hydrology) in combination with the Indian Monsoon Data Assimilation and Analysis dataset (1980–2020), researchers reconstructed long-term discharge patterns of the glacier system.

The study found that the mean annual discharge of the GGS over the four-decade period stood at 28±1.9 cubic metres per second. The bulk of this came from snowmelt (64%), followed by glacier melt (21%), rainfall-runoff (11%) and base flow (4%). Peak discharge occurs in July, averaging 129 cubic metres per second.

Importantly, the study observed a shift in seasonal discharge. Before 1990, peak flows typically occurred in August. Since then, the peak has moved to July, which researchers attribute to declining winter precipitation and enhanced melting earlier in summer.

Between 1991–2000 and 2001–2010, mean decadal discharge rose by 7.8%. While annual temperatures showed a steady increase, no significant change in overall precipitation or glacier melt was recorded. Snowmelt, however, declined due to reduced snow cover, while rainfall-runoff and groundwater contributions increased. According to The Hindu, statistical analysis indicates that summer precipitation and winter temperatures are the dominant controls on annual discharge levels.

The results, scientists say, reveal clear warming-induced changes to hydrological processes in the GGS. Increased rainfall-runoff and base flow point to altered monsoon dynamics, while reduced snow cover underscores the vulnerability of Himalayan cryosphere systems.

This year’s unusually heavy monsoon in north India - about 25% above normal between June and August - and recurrent flood events in Uttarakhand, Himachal Pradesh and Jammu have drawn fresh attention to the fragility of these mountain catchments. As The Hindu notes, such events are often hastily attributed to “cloudbursts” by State authorities, despite limited scientific evidence or real-time monitoring tools.

A true cloudburst is defined as rainfall exceeding 10 cm within an hour over an area smaller than 30 sq km. While climate change may increase the likelihood of such extreme events, the study underscores the urgent need for robust field data, satellite monitoring and advanced modelling to improve water management in glacier-fed basins.

With the Hindu Kush Himalaya often referred to as the “water tower of Asia”, changes in the Gangotri system have implications that extend well beyond Uttarakhand. Scientists warn that altered flow regimes could affect agriculture, hydropower and downstream water availability for millions dependent on the Ganga basin.

As The Hindu report highlighted, sustained research and monitoring of smaller glacier-fed systems such as GGS are essential to anticipate future water challenges and guide climate adaptation strategies.