WESTERN HIMALAYA HEATING FASTER THAN THE EAST; STANDS TO LOSE MOST SNOW IN COMING YEARS: STUDY

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A new study combining 120 years of observed temperature records (1901–2020) with eight global climate models finds that the western Himalaya (Ladakh, Jammu & Kashmir and Himachal Pradesh) is warming faster than the central and eastern stretches of the range, in every season and under every emission scenario tested. Winter is warming faster than spring, night-time temperatures are climbing faster than daytime highs, and springtime snow loss over the western Himalaya could be three times larger on a high-emission pathway than on a low-emission one by the end of the century.

A research study, , published in the Journal of Earth System Science, led by the Department of Remote Sensing and Geoinformatics, Birla Institute of Technology (BIT), Mesra, Ranchi, with the Indian Institute of Tropical Meteorology (IITM), Pune, and Ashoka University, assessed how temperature and snow are changing across three sectors of the Indian Himalayan range, and how far that change could go by 2100.

The team used two kinds of evidence. The first is a 120-year record of actual temperature measurements across the region, running from 1901 to 2020. The second is a set of eight global climate models, first checked against what has already happened and then run forward to 2100 under five possible futures — from a world that cuts emissions sharply to one that keeps burning fossil fuels at the current pace.

Two seasons are examined: winter, when snow builds up, and the pre-monsoon spring months, when it melts. The range is split into three stretches, studied separately: the western Himalaya (Ladakh, Jammu & Kashmir, and Himachal Pradesh), the central Himalaya (largely Uttarakhand), and the eastern Himalaya (Sikkim, Arunachal Pradesh, and the wider North-East). Between them, they hold more than 15,000 glaciers and feed the Indus, Ganges and Brahmaputra, the rivers that roughly 1.5 billion people depend on.Vulnerability of the Himalayan region under the climate change

The warming has already reached about 1°C, and it is not evenly spread Compared with the first three decades of the 1900s, all three stretches of the range had already warmed by close to 1°C in winter by the two decades to 2014: 1.06°C in the western Himalaya, 0.96°C in the central Himalaya and 1.09°C in the east. Springs had warmed by 1.08°C in the west, and 0.83°C in the centre and east. The warming has not arrived at a steady pace. Warmer-than-normal years have become the rule rather than the exception across all three stretches over the past 20–30 years, most of the change has come recently, the study said.

“The Himalaya is often discussed as a single system, but our observations and models both say otherwise. The western Himalaya consistently emerges as the most sensitive stretch — it warms the most and loses the most snow under every pathway we tested. That has direct consequences for the states that sit in it,”said Protyusha Mukhopadhyay, lead author, Birla Institute of Technology (BIT), Mesra.

Under high emissions, western Himalayan winters may warm by more than 7°C

The models show the same west-to-east pattern throughout the century. If emissions stay high, winters by 2081–2100 would be 7.18°C warmer in the western Himalaya, 6.71°C warmer in the central Himalaya and 5.82°C warmer in the east, compared with the early 1900s. Springs warm in the same order: 6.91°C, 6.41°C and 5.16°C. “In the west and centre, winters are warming faster than springs. Less snow on the ground would mean a darker surface, which absorbs more heat, which melts more snow. It matters because winter is the season in which snow is supposed to build up; warmer winters mean less snow banked for the melt months that follow,” said Parthasarathi Mukhopadhyay, corresponding author, Ashoka University.

Nights are warming faster than days

One of the clearest signals in the observational record is that minimum (night-time) temperatures are rising faster than maximum (daytime) temperatures across the western and central Himalaya. In the western Himalaya, winter minimum temperatures rose 1.23°C against 0.87°C for day temperatures; in spring, 1.25°C against 0.91°C. In the central Himalaya the gap is wider still in winter (1.20°C against 0.72°C).

The eastern Himalaya is the exception, where winter maximum temperatures rose more (1.19°C) than minimum (0.99°C). Warmer nights matter because they shorten the hours in which snow and ice can refreeze. That speeds up melting, and changes when the meltwater reaches the rivers below. said “Rising night-time temperatures are the quieter half of this story, and arguably the more consequential one. When the cold nights that let snowpack recover start disappearing, you change the melt cycle itself rather than how much snow falls, but when the water arrives downstream,” Dr Swagata Payra, co-author, BIT Mesra.

Spring is where the snow is being lost

In all three stretches, more snow is lost in spring than in winter, and by far the most is lost in the west. The study measures this as the weight of snow sitting on each square metre of ground. Over the western Himalaya, spring snow falls away steadily even on the lowest-emission path: by 24.2 kg per square metre by 2040, 27.4 kg by 2060 and 32 kg by the end of the century. On the highest-emission path, that end-of-century loss reaches 95.9 kg per square metre, enough to point towards an almost complete loss of seasonal snow in some pockets of the region, the authors said. The central Himalaya loses less, though still a substantial amount: between 17.0 and 34.9 kg per square metre by the end of the century, depending on the emissions path. The eastern Himalaya loses the least, between 5.5 and 11.1 kg. Winter follows the same pattern. Western Himalayan snow loss by the end of the century ranges from 9.5 kg per square metre on the lowest-emission path to 53.2 kg on the highest.

The gap between emission pathways

Western Himalayan winters end the century 2.55°C warmer if emissions fall sharply, or 7.18°C warmer if they do not (a gap of 4.6°C). On spring snow, the high-emission path costs the region three times as much as the low-emission one; on winter snow, more than five times as much. The eight models largely agree on the next two to three decades. They diverge much more towards 2100 because how much the region warms by then depends on choices that have not yet been made. said The eastern Himalaya warms the least of the three and loses the least snow, and its outlook varies theleast across the emission paths.

However, the study notes that the east has become a hotspot for glacial lake outburst floods that are sudden, destructive floods released when a lake dammed by glacial debris gives way. “That risk is expected to spread westward in the future, driven by retreating glaciers and the new lakes they leave behind, not by temperature alone,” said “The models agree on where we are headed over the next two to three decades. What remains open is the second half of the century, and that is determined by emissions rather than by anything intrinsic to the mountains. A low-emission pathway does not stop the warming, but it changes its magnitude by several degrees,” MukhopadhyayProtyusha.

What the researchers recommend

The authors call for region-specific climate services and adaptation policy; enhanced monitoring that combines in-situ networks, satellite products and sustained high-resolution modelling to track glacier and snow dynamics in near real time; strengthened early-warning systems; sustainable water management; community-level resilience programmes; and transboundary cooperation. How water actually moves through these high mountains is still poorly captured by models, and more measurement on the ground is needed before it can be said with confidence how much ice and snow melts each year, and how much of that reaches the rivers below, the authors said.