There are fears the number of casualties may rise, as severe weather and difficult terrain, worsened by rain damage, are making rescue operations difficult.
The disaster has cut off communication lines with neighbouring Sikkim with an iron bridge near Teesta Bazaar in Kalimpong collapsing.
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In several episodes of heavy rainfall recently in India, landslides have caused major damage. While India has done well to prepare and safeguard itself against certain natural events such as cyclones, landslides landslides continue to remain a threat. An early warning system is still being tried out, and pressures from population, development, and infrastructure projects have increased vulnerability.
What exactly are landslides, and why does India remain especially vulnerable to them? We explain.
What is a landslide?
A landslide is literally land — mud, rocks, debris — sliding down a slope. Landslides occur when the force of gravity becomes stronger than whatever ‘glue’ was holding this material together. The glue can be a combination of various factors, including tree roots holding soil together, the gradient of a slope, the weight and mass of the soil, channels available for water to move through the soil and down the slope, etc.
The reason heavy rain often triggers landslides is that water makes the soil heavier and also reduces friction, making it easy for the soil and rocks to slide down a slope.
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In India, especially in the hills, unplanned construction has worsened matters. Buildings and roads are often built without accounting for how much load a slope can hold, while improper drainage networks leave water with no avenue to flow out safely. In the plains, even if extreme rainfall takes place, water has more space to spread out.
Why are landslides such a big danger in India?
Because an adequate early warning system is yet to be developed. For cyclones, for example, warning generally comes well in advance for evacuation and relief efforts to mobilise. For heavy rainfall too, predictions come at least a day early.
A house partially buried under debris after landslides due to heavy rainfall, in Darjeeling district, West Bengal, Sunday, Oct. 5. (PTI Photo)
For example, the India Meteorological Department (IMD) had forecast Saturday’s spell of rainwater in the hills, which is due to a low pressure system approaching Bihar. But when an episode of heavy rainfall will trigger landslides is still difficult to pinpoint.
About 0.42 million square km of India’s landmass, or about 13% of its area, spread over 15 states and four Union Territories, is prone to landslides, according to the Geological Survey of India (GSI). This covers almost all the hilly regions in the country. About 0.18 million square km, or 42% of this vulnerable area is in the Northeastern region, where the terrain is mostly hilly.
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As human activity-related pressures rise and climate becomes more erratic, the way forward is developing warning and mitigation mechanisms.
The National Disaster Management Authority (NDMA) has been working with GSI and other agencies to manage the risks from landslides. A National Landslide Risk Management Strategy was finalised in 2019, which talked about vulnerability mapping, identifying the most vulnerable locations, development of an early warning system, and preparation of mountain zone regulations. But most of the work still remains to be done.
Some early warning systems have been developed, on a trial basis at a few locations in Kerala, Sikkim, and Uttarakhand. These warning systems are linked to rainfall forecasts from IMD. The rainfall prediction is combined with soil and terrain information to calculate whether it is likely to result in displacement of land. However, they are yet to take off in a big way.
