Study maps 34 years of Uttarakhand glacier retreat, finds average of 23.23 metres a year

Glaciers across Uttarakhand’s Central Himalaya are retreating by an average of 23.23 metres a year, with some losing ice at rates of up to 88 metres annually, according to a new study that found rising temperatures, glacier characteristics and topography are shaping the pace of ice loss.

The study, “Time-dependent assessment of glacier recession in the Indian Central Himalaya”, which is based on observations and satellite imagery from 1990 to 2024, also found that the equilibrium line altitude has risen by nearly 500 metres in some regions since 2000.

Published in Discover Geoscience earlier this month, the study was conducted by Manish Mehta of the Wadia Institute of Himalayan Geology in Dehradun, along with Jyoti Kumari, Girish C Kothyari and Atul Kumar Patidar of the University of Petroleum and Energy Studies (UPES), Dehradun.

According to Mehta, the study found that the average frontal retreat rate across the Central Himalaya was 23.23 metres a year. “Although the response varied substantially between individual glaciers, retreat rates ranged from about 3.7 metres per year for relatively stable or heavily debris-covered glaciers such as Bhagirathi (Bhagirathi valley, Uttarkashi district) and Satopanth (Chamoli district) to as much as 88 metres per year for Khatling Glacier (Bhagirathi valley, Tehri Garhwal), a clean-ice glacier,” he said.

The study found a marked difference in retreat rates between clean-ice and debris-covered glaciers. Clean-ice glaciers are particularly vulnerable to rapid thermal ablation, or ice loss caused by melting, while those terminating in pro-glacial lakes (lakes formed directly in front of, beside or beneath a retreating glacier) are also exposed to ice loss through calving, when large pieces of ice break off into a lake. Milam Glacier in Pithoragarh district’s Milam valley, for example, has spawned nearly 47 new glacial lakes, according to the study.

In contrast, glaciers covered by thick layers of debris can experience significantly lower melt rates, as the debris acts as a natural insulating shield. The study found that glacier retreat is not uniform and is influenced by a combination of regional climatic changes and local physical characteristics.

Another major finding relates to the equilibrium line altitude (ELA), the boundary separating the zone of net snow accumulation from the zone of net melting. The study found that the ELA has risen by nearly 500 metres in some regions since the beginning of the century.

Mehta said the rise has reduced the amount of fresh snow available to glaciers and pushed their mass balance further into the negative. “This means less snow is being added to the glacier while more ice is being lost through melting and other processes. As a result, the glacier’s mass balance becomes increasingly negative or, in simple terms, it is losing more ice than it is gaining each year,” he said.

The study also identified the period around 2000 as an important climatic turning point. Meteorological and reanalysis datasets showed that the late 20th century, particularly 1980-1999, was characterised by a pronounced “warming-drying” trend, with declining precipitation and steadily rising temperatures. The post-2000 period, however, shifted towards a more humid phase, with increasing precipitation trends. The study found that the increased precipitation and snow accumulation after 2000 provided a temporary buffer to some eastern debris-covered glaciers and somewhat slowed their retreat rates.

Despite this temporary effect, rising temperatures continued to drive overall glacier volume reduction and dynamic thinning across the high-altitude cryosphere, indicating that increased precipitation alone has not reversed the longer-term loss of glacier ice, the study added.

While atmospheric warming remains the primary driver of deglaciation, the study found that local and non-climatic factors play a substantial role in determining how individual glaciers respond. Glacier geometry, slope, aspect and the shape index together account for up to 46% of the local variation in ice loss.

The study also found that elongated glaciers with higher shape indices — those with a more elongated or irregular shape relative to their overall size — tend to maintain better structural integrity and stronger ice flux from their accumulation zones. Ice flux refers to the movement of glacier ice from the upper snow-accumulation area towards the lower part or glacier front. Smaller, more circular glacier fragments, by comparison, are more vulnerable to rapid thermal breakdown.

Glacier orientation also matters, the study found. South-facing glaciers, which receive greater exposure to direct sunlight, have shown disproportionately higher shrinkage than their north-facing counterparts.

Mehta said the findings point to a complex interaction between climate and local topography in determining glacier survival. “Although regional warming is driving widespread deglaciation, debris cover, glacier geometry, slope orientation and other physical characteristics can either accelerate or buffer the loss of ice,” he said.

The researchers said the findings have major implications for regional hydrology, natural hazard management and long-term water security. The Ganga basin supports around 800 million people, making changes in the Himalayan region particularly significant for downstream populations. “With cumulative glacier lengths projected to shrink significantly in the coming decades, there is a need for enhanced and methodologically consistent monitoring of the region’s glaciers,” he said.

The study recommended combining satellite radar, unmanned aerial vehicles (UAVs) and targeted field surveys to improve understanding of remaining freshwater reserves and the continuing changes in glacier mass, length and dynamics. Such monitoring would also help improve the assessment and mitigation of hazards associated with rapidly changing glaciers and glacial lakes, including glacial lake outburst floods (GLOFs).