The unstudied crisis of Himalayan nallahs: Flooding under a scorching sun

 

A new report by Parineeta Dandekar of the South Asia Network on Dams, Rivers and People (SANDRP) has brought to light a recurring and largely unstudied crisis in the Indian Himalayas: the phenomenon of glacial streams, or nallahs, experiencing devastating flash floods not from rainfall, but under a blazing sun.

The report, titled "Flooding Under the Scorching Sun: The Unstudied Crisis of Himalayan Nallahs," details the catastrophic and repeated flooding of the Jahlma Nallah in Himachal Pradesh's Lahaul and Spiti district. This crisis, which has been intensifying for the past five years, has cut off hundreds of villages, destroyed livelihoods, and highlights a critical gap in scientific understanding and governmental response.

The Jahlma Phenomenon: A Diurnal Disaster

According to the report, the Jahlma Nallah, which originates from the Pir Panjal range and feeds the Chenab River, has been exhibiting a bizarre and terrifying pattern. On the afternoon of June 29, 2026, and repeatedly on subsequent days, the nallah transformed from a thin flow into a "terrifying, brown debris-laden force".

Residents like Jagdish ji of Lindur village have noted a distinct diurnal fluctuation: the floods quieten at night and in the cool early mornings, only to "gather force around noon," coinciding with the peak of the sun's heat. "The sun was so hot, we knew the floods would be coming," Jagdish ji is quoted as saying. This phenomenon occurs in the absence of any rain, snowfall, or cloud cover.

"There are no substantial glacial lakes upstream to cause Glacial Lake Outburst Floods (GLOF)," the report clarifies, dismissing the most common cause of Himalayan flash floods. "Nor is it a one-time happening." The floods have become a cyclic phenomenon for which "we honestly have no clue what is happening. Or why it is happening."

The consequences are devastating. The floodwaters carry a massive load of debris and sediment, blocking the Chenab River and destroying the vital bridge across the Jahlma Nallah, which forms part of the strategic SKTT road connecting the region to Manali via the Atal Tunnel. The report states that "for the past five years, one month of connectivity is being lost to the floods of Jahlma Nallah."

Permafrost Thaw: A Key Suspect in a Complex Puzzle

While the exact cause of the flooding remains a mystery, the report points to a critical factor: the rapid thawing of permafrost. Two studies conducted in the aftermath of the 2023 disaster, one by IIT Mandi and another by the Geological Survey of India (GSI), offer crucial insights.

The IIT Mandi report established that the Lindur village area is experiencing "permafrost melt induced subsidence" at a rate of 7.9 cm per year. The region is surrounded by rock glaciers—masses of rocks and boulders held together by an ice core. As global temperatures rise, this ice is melting, destabilizing the slopes and leading to land subsidence. "The orientation of the cracks is towards the riverbed and sub-surface ice melting water flowing to the Jahlma nala river," the report stated.

However, the author of the IIT Mandi report, Dr. Dericks P. Shukla, admitted to the SANDRP team that the exact cause of the large-scale flooding is unclear. He posited that "thin debris covering the ice, which is not insulating enough, could be causing enhanced melting." He further noted the presence of "cracks as wide as 2 feet, with a depth of 20 feet near the glacier." Dr. Shukla emphasized that "we need gauging stations for water and silt on the Nallah to know what’s happening."

The report notes that while permafrost thaw is known to cause rock glacier destabilization, as documented in recent studies from the Alps and hydraulic research, the Jahlma Nallah's floods are unique in their diurnal nature and immense scale. Globally, no parallels have been found for this phenomenon.

Human Impact and a Governance Vacuum

The crisis is not just a scientific anomaly; it is a humanitarian one. The region has only one growing season, and the Jahlma Nallah floods during the peak harvest time. "The cold region has only one growing season, and the precious cauliflowers, lettuce and peas harvested now will wilt in a matter of days if they do not reach the market," the report states.

Villagers are forced to carry their harvests on their backs across the sludge. Farmers from villages like Jahlma, Jasrath, and Jobrang are left stranded with their produce. In one harrowing account, a marriage party had to walk across the debris after the bridge collapsed. In another, a severely ill old woman was transported across the nallah using the arm of a JCB excavator.

The report highlights a significant governance failure. Despite the repeated devastation, there is no automated weather station or discharge gauge on the Jahlma Nallah. The Band-aid measures of repeatedly rebuilding bridges and roads have proven futile as they are washed away again.

"The Departments just work in silos," a source told the report's author. The Himachal Pradesh State Disaster Management Authority has reportedly been unable to finalize key projects like the National Glacial Lake Outburst Floods Risk Mitigation Programme (NGRMP) for more than three years.

A Wider Himalayan Crisis

The report warns that Jahlma is not an isolated case. Similar situations are being seen in other nallahs like Shansa, Karpat, and Jispa in Lahaul, and Dhondhal Nallah in the Miyar Valley, which have experienced rainless flash floods this year. In the remote Pangi Valley, elders are "aghast" as nallahs, which have never flooded without rain, are now doing so regularly.

As the monsoon sets in, the region will face additional challenges from landslides and cloudbursts, making it even more difficult to study this phenomenon. With permafrost thaw accelerating, the report calls for an urgent, systemic, and scientific study of these Himalayan nallahs to understand and mitigate this emerging crisis before more lives and livelihoods are lost.