A landslide site.
Credit: PTI
Kolkata: The increasing frequency and intensity of landslides across India is no longer just a consequence of natural topography, but a combination of changing rainfall patterns, climate change, deforestation, and constructions in ecologically sensitive areas, a senior official of the Geological Survey of India (GSI) said on Sunday.
Noting that though pollution is not a direct trigger for landslides, he said that air pollution and greenhouse gas emissions are, however, key contributors to climate change, altering rainfall patterns across many parts of the world, including India, significantly increasing the risk of landslides in geologically sensitive areas such as Uttarakhand and Himachal Pradesh.
"The combined factors, namely, the geological makeup, climatic conditions, and increasing anthropogenic pressure together make our hilly regions particularly vulnerable to landslides," GSI Director General Asit Saha told PTI in an interview at the scientific agency's headquarters here in Kolkata.
"While India has long been vulnerable to landslides, particularly in the Himalayas and Western Ghats, what we are witnessing in recent times is an increasing frequency and intensity of landslides, driven by both natural and anthropogenic factors, often acting in combination. Similarly, the formation and subsequent breach of glacial lakes, often formed due to landslides damming river valleys in the upper reaches of the Himalayas, have emerged as serious hazards causing downstream flooding and slope instability.
"Overall, we can say that the rise in landslide events in India is a result of both changing climate patterns and escalating human interventions, often acting together to destabilise slopes," he said.
Elaborating on the possible reasons behind the rise in the incidents of landslides in the hills and mountains of India, the geoscientist cited several causes.
"These areas naturally have steep slopes, inherently more susceptible to gravitational movement of rock, debris, or soil. Even minor disturbances, whether natural or human-induced, can destabilise such slopes.
"Secondly, many of these regions are tectonically active zones. The geological formations here are often young, fractured, and highly weathered, making them structurally weaker and more prone to failure during intense rainfall or seismic activity," Saha said.
Besides, pointing to monsoonal rain playing a big role behind the increase in the rise of landslide incidents, he also held human activities of constructions on unstable slopes, disrupting natural drainage systems, leading to destabilising the terrain.
"The prolonged or heavy rainfall typical of the Indian monsoon increases the moisture content in soil and rock, leading to higher pore pressure and reduced cohesion, both of which contribute significantly to landslides.
"And then there is the role of human activity: developmental activity, deforestation, road construction, and expansion of existing infrastructure, especially on unstable or unengineered slopes, which many a time disrupt natural drainage systems and further destabilise the terrain," the geologist said.
Further, he pointed to "deforestation and land degradation" as long-standing concerns behind incidents of landslides.
"Our investigations and landslide susceptibility mapping studies have consistently shown that removal of vegetation cover significantly reduces slope stability," he said.
The GSI official also said that though the agency has not undertaken specific studies linking pollution directly to landslides, it believes that pollution, "as part of the larger climate change dynamic, is a contributing factor to environmental changes that heighten the risk of such disasters".
Geologists, through their National Landslide Susceptibility Mapping (NLSM) programme, have identified several areas along the entire Himalayan belt, from Jammu and Kashmir and Himachal Pradesh to Uttarakhand, Sikkim, and Arunachal Pradesh as the most susceptible to landslides, he said.
They have also identified areas in peninsular India, like the Western Ghats, particularly in Kerala, Karnataka, and Maharashtra, as well as the Nilgiris in Tamil Nadu and the Konkan coast, as high-risk areas, Saha added.
"Together, these landslide-prone regions span approximately 0.43 million sq km and including permafrost zones, the total landslide-prone area expands to 0.49 million sq km," he elaborated.
Till August this year, India has experienced multiple deadly landslides, particularly in the Himalayan states, during the ongoing monsoon season.
Major incidents have occurred in Jammu and Kashmir, Uttarakhand, and Himachal Pradesh, often triggered by heavy rain, cloudbursts, and flash floods.
This month itself, India witnessed a massive landslide near the Vaishno Devi shrine, killing at least 30 people. The disaster followed record-breaking rainfall that also caused widespread flooding. In the earlier weeks of August, cloudbursts and heavy rain in the Ramban and Reasi districts led to flash floods and landslides, resulting in multiple deaths and blocking the Jammu-Srinagar national highway for days.
In Uttarakhand, a cloudburst caused a major mudslide, destroying parts of Dharali in Uttarkashi district, leaving at least four people dead and dozens missing.
In late June, Himachal Pradesh recorded numerous landslides, cloudbursts, and flash floods in the districts of Mandi, Kullu, and Chamba.