‘We cannot develop the mountains like plains’

For the Western Himalayas, the 2025 southwest monsoon has been unusually severe, with consistent reports of disasters. Uttarakhand, for example, has seen surplus rainfall in more than half its districts since June. The state has also experienced catastrophes such as the August 5 debris flow in Dharali, which wiped away its entire market; and more recently, the downpour and flash floods in Dehdradun that has so far left nearly 20 people dead and dozens of buildings and roads damaged.

These disasters bear the signatures of climate change, brought on by anthropogenic triggers, says Swapnamita C Vaideswaran, scientist with the Wadia Institute of Himalayan Geology, Dehradun. In an interview with Down To Earth, Vaideswaran speaks of the climate-induced changes in the Western Himalayas, the impact of rapid development in the region, and the future risks for the terrain.

Dakshiani Palicha: This monsoon season has been quite unusual, and the Western Himalayan region in particular has been battered by frequent, strong weather disasters. What are the possible triggers for them?

SV: At the start of the monsoon season, the India Meteorological Department (IMD) forecasted a neutral year with a normal rainfall. However, as the season progressed, we began to see numerous western disturbances. The influence of these systems [western disturbances are essentially extratropical storm systems that originate in the Mediterranean region and bring winter rainfall and snowfall to northwestern parts of the Indian subcontinent] is generally prevalent in the winter months and recedes around April. But they tend to linger if influenced by a warming event or an impact of anthropogenically induced climatic change.

So to some extent, the entire Himalayas experienced climate-induced geohazards. Consider Dharali, which I visited shortly after the debris-flow disaster. What I saw was a very clear-cut warning about climate change. People speculated that the debris flow was caused by an avalanche or glacial collapse. The focus was on the Khir Ganga river which affected the Dharal Fan [Dharali is situated on an alluvial fan formed by deposits of sediments from the Khir Ganga], and the Tel Gad, which affected the Harsil Lower Camp, because that is where the settlement was and lives were lost. But it affected a much wider area. This disaster was actually a case of a very typical orographic phenomenon induced by climate change—heavy rainfall at a place higher up than Dharali, at 4,000 metres above the sea level. This is a place where we only expect snowfall, not rain. Even in Harsil, which is at an elevation of 2,500 metres, we only expect drizzles.

A similar occurrence was seen in Nanda Nagar in Chamoli district, north of Tharali village. People began to notice cracks on the ground, like those in Joshimath. These cracks are a result of heavy rainfall which has been saturating the ground at least for the past decade. A week or so ago, Tharali was hit by a devastating flash flood.

We have plotted 100 years of climate data and it shows that temperature is on the rise. Rainfall is decreasing overall, but is confined to extreme events which occur with higher intensity. These are all signatures of climate change that have increased over the last decade. Still, we do not know whether every year from now on will tell the same story.

DP: Why is it difficult to pinpoint the cause of disasters like the Dharali flash floods?

SV: Every time we have an incident like a flash flood, social media is flooded with experts from foreign countries, offering explanations. They are able to do so because they have access to satellite data. In Dharali, we could not pinpoint the cause because cloud-free satellite data was not available for quite some time. Dharali was also cut off due to inaccessible roads which could not facilitate experts to go for evaluation.

I went to Dharali four days after the flood, because I knew it was too cloudy to get data remotely. Teams from the state administration, the Indian Army, the state disaster response force, the Nehru Institute of Mountaineering and other agencies extended all their support to my team. We did everything possible to collect the ground signatures from the higher altitudes.

The observed rainfall at higher altitudes was unexpected. But Harsil, in the valley, saw hardly any rain, and existing stations failed to quantify the rain in higher altitudes.

DP: What kind of monitoring and planning do we need to gauge, and minimise, the impacts of flash floods and disasters on the fragile landscape?

SV: What I lacked when I went to Dharali was a very good base map. I had a toposheet, which was on a scale of 1 cm to 250,000 km. That was not enough. I needed data of much better resolution to see Dharali and the whole fan and to analyse how it existed earlier and how it has changed over time.

We conducted drone surveys and did LiDAR (Light Detection and Ranging) mapping to recreate the earlier Dharali fan and compare it with the landscape now. We were able to understand how much debris had accumulated because we also had the base map. Drone surveys helped see how much material was brought down and how the fan has expanded.

Dharali is still a new, soft fan, so now we need to monitor the erosion. We will also have to monitor its development as a new town—the recent flash flood will soon be forgotten, and new houses will emerge on the fan. We have seen this pattern before: when disasters strike, we focus on immediate remedies and then move on. There is no planning or foresight.

We need to create high-resolution topographic maps of all the mountain states in their entirety. We cannot only look at small parts on their own. Gone are the days when we used to create the susceptibility maps for landslides. Now we need to map flash-flood and debris-flow susceptible zones and high-resolution LiDAR mapping for every region to understand the risk zones. 

DP: The Himalayas are also now being developed at a rapid pace. Does this influence the frequency and intensity of disasters in the region?

SV: Let’s first look at population—I talk about this frequently, but it is a fact that it is adding to the burden. We have a large number of people visiting the mountains now, and wanting to change the culture and landscape according to their expectation. But mountains cannot be plains, just as plains cannot be mountains. We are seeing how small variability is inducing disasters at local levels. Places like Kedarnath, Badrinath are located very close to significant glaciers. But let us also not forget the smaller cirques and hanging glaciers on the tourist routes. They are the most fragile. Also, Dharali, which is a fan on the Khir Gad and the Bhagirathi river, was not supposed to be developed into a town. We are simply expanding our mountain towns to beyond their capacity to accommodate the growing population and the transient tourists.

Another factor is the construction of roads. We often only concentrate on the national highways, but we should also look at the Prime Minister Gram Sadak Yojana (PMGSY) roads. Whether a geotechnical input can help plan the PMGSY construction better needs to be looked at. Like every slope on the mountain cannot have a road, every litho-structural unit cannot be cut across. A cut-slope topography, that is when you cut the bottom of the slope for a road, is vulnerable if the dip of the beds, or shearing and deformed rocks are not conducive. Then the slope collapses. But we are not paying much attention to this.

In contrast, people blame the hydropower projects, which are actually not the biggest culprit. We now have run-of-the-river schemes and good technology to construct tunnels in large mountains. All we need to do is ensure that these projects finish on time. Project delays are damaging.

DP: What is it about the geology and topography of the Himalayas that makes the region so vulnerable to disasters? Why are the impacts so acutely felt in the region?

SV: The Himalayas are seismo-tectonically active. That means we are expected to have micro to large earthquakes. There is a constant on-climate-tectonic interaction; the tectonic processes control the climatic processes. All the processes work together to modify the topography and landforms. The topography will always try to balance itself. But the climatic processes are influenced by anthropogenic activities to a big extent. There is a natural climate–tectonic relationship, but when climate disturbances occur, we end up seeing more impacts.

DP: Is this imbalance altering the Himalayan geomorphology in a drastic or irreversible manner?

SV: When the earth is gearing up for enhanced tectonism, it generally sends some signals—more landslides or deformations on the ground. This is why we monitor where more deformations are being seen, through SAR (Synthetic Aperture Radar) and GPS. We try to understand if active deformations indicate an impending seismic event. We may see micro earthquakes in the Himalaya with our dense seismic networks. We need to correlate if micro-activities are also inducing land deformations.

But the disasters we are seeing now actually indicate a very surficial deformation. Floods result in slides, debris come down and fans come up. These are transitional deformations in the context of geomorphology. Our rivers are very active and do not keep very superficial deformations for long. This fan created in Dharali will probably become half of its size in five years.

I see different risks for the future. Right now, we see flash floods that can kill hundreds of people, but what we are not seeing is the future picture, which is climate change melting our glaciers and occurrence of intensified rains. Such rain never recharges our groundwater. All freshwater just runs off as surface flows. We could face a drought-like situation in the future. It happened during the Indus Valley Civilisation; the Indus River had a lot of water, but the earth was emerging from the Ice Age and glaciers were melting. Soon, periods of droughts happened, which eventually collapsed the whole civilisation. We also may anticipate future water risks.

Part of this interview was published in the September 16-30, 2025 print edition of Down To Earth