Context: This article is based on the news “IIT Delhi team makes first hi-res landslide risk map for India” which was published in the Hindu. Indian Institute of Technology Delhi has made the first high-resolution landslide susceptibility map for India and the map data is available for free.

National Landslide Susceptibility Map: Background

• In late 2023, torrential rain during the northeast monsoon triggered heavy floods and landslides in multiple States in India, killing hundreds of people.
• It highlights the need for a national landslide susceptibility map to identify the most dangerous areas and help allocate resources for mitigation strategies better. 

About National Landslide Susceptibility Map

• The team from IIT Delhi built a national landslide susceptibility map that uses the latest data and data collection and mapping techniques. 
  • High Resolution: The map, could plot the susceptibility at a resolution of 100 m. 
  • Identified Region: The map acknowledged some high landslide susceptibility, like parts of the foothills of the Himalayas, the Assam-Meghalaya region, and the Western Ghats. 
  • New Insight: It also revealed some previously unknown places with high risk, such as some areas of the Eastern Ghats, north of Andhra Pradesh.

• Leveraging Ensemble Machine Learning Technology: Ensemble machine learning is when multiple machine learning models are used together to average out an oversized impact from any one model.
• Factors Used: They collected information on factors like soil cover, number of trees covering the area, distance from roads or mountains, etc. 
  • They used GeoSadak, an online system with data on the national road network in India, displaying data on roads located outside cities.

About Landslides in India

• Definition of Landslide: It is a movement of a mass of rock, earth, or debris down a slope. 
• Landslide Prone Regions: The regions with fewer trees, closer to road-building activity, and steeper local slopes are more unstable and prone to landslides.

Causes of Landslides in India  

• They can occur on many types of terrain given the right conditions of soil, rock, geological structure, drainage, and slope.
  • Natural Causes: Rainfall, undercutting of slopes due to flooding or excavation, earthquakes, snowmelt, etc. 
  • Anthropogenic Causes: Overgrazing by cattle, terrain cutting and filling, excessive development, etc. 
    • For example, land use changes lead to deforestation and exposure of slopes cut for the development of a key railway project likely contributed to a deadly landslide in the  western Manipur in 2022.

Types of Flows

• Debris Flow: It is a form of rapid mass movement in which a combination of loose soil, rock, organic matter, and slurry flows downslope. They are commonly caused by intense precipitation or rapid snow melt. 
• Earth Flow: It is a downslope viscous flow of fine-grained material saturated with water. 
• Mudflow: A mudflow is a wet or viscous fluid mass of fine and coarse-grained material that flows rapidly along drainage channels. 
• Creep: Creep is the slow, steady, downward movement of material under gravity that occurs in a large area.

Must Read: Interconnected Disaster Risks Report 2023 – UNU-EHS

Overview of Landslides in India

• Increasing Landslides in India: Over the past 50 years, the landslides seem to have increased in magnitude and frequency due to human activities. 
  • For instance, India has improved and expanded its road network in mountainous states under the national Bharatmala Pariyojana (“Road to Prosperity”) initiative. 
  • However, the Copernicus organization recorded more than one landslide per road kilometer along the NH-7 between Rishikesh and Joshimath.

ISRO’s Landslide Atlas of India Findings 

• Global Standing in Landslide Risk: India is among the top five landslide-prone countries globally, where at least one death per 100 sq km is reported in a year.
• Rainfall variability Pattern:  Primary cause of landslides with the Himalayas and the Western Ghats remaining highly vulnerable.
• Land Area Prone to Landslide: Excluding snow-covered areas, approximately 12.6% of the country’s geographical land area.
• Regional Variability: 66.5% of the landslides are reported from the North-western Himalayas, about 18.8% from the North-eastern Himalayas, and about 14.7% from the Western Ghats.

Landslides in the Himalayas

• They have been observed to be the most frequent landslide incidents, because the Himalayas are a comparatively young mountain system and the rock structure is still weak and fragile. 

Major Causes of Landslides in India

External Causes of Landslides

• Undercutting of the foot of the hill slope due to river erosion, quarrying, excavation for canals and roads, etc. 
• Increase in external  loads  such  as  buildings,  reservoirs,  highway  traffic,  stockpiles  of  rocks, accumulation of alluvium on slopes, etc. 
• Increase in unit weight of slope material due to increased water content. 
• Vibrations  due  to  earthquakes,  blasting,  traffic,  etc.,  causing  an increase  in  shearing stresses.  
• Anthropic changes caused by deforestation 
• Undermining caused by tunneling, collapse of underground caverns, seepage erosion, etc. 

Internal Causes of Landslides

• Increase in pore water pressure. 
• Reduction in cohesive strength caused by progressive lateralization. 
• Cracks due to alternate swelling and shrinkage from tension. 
• Presence of faults, joints, bedding planes, cleavage, etc., and their orientation. 
• Freezing and thawing of rocks and soils. 
• Material properties such as compressive strength, shearing strength, etc., of earth material.

Impacts of Landslides

• Economic Impacts: Landslides cause extensive damage to houses, roads, buildings, forests, plantations, and agricultural fields. 
  • According to the Department of Revenue of the Himachal government, Himachal Pradesh has an estimated cost of damage from flood and landslides at over Rs 3738 crore due to the widespread destruction caused by torrential rains during the monsoon from June 24 to July 14 in 2023.
• Social Impacts: In landslide disasters, casualties may not be widespread, except when associated with earthquakes or volcanoes. Fatalities are more where population pressure has prompted settlements in areas vulnerable to landslides. 
  • According to the Statement of Climate of India 2022 released by the Indian Meteorological Department (IMD),  heavy rain, floods and landslides claimed 835 lives in India in 2022.
  • Kerala landslide 2021: More than 20 people died in landslides and flooding triggered due to heavy rain. According to India’s National Emergency Response Centre (NERC), 5,223 people have been displaced and moved to 163 temporary relief camps.
  • Mumbai Landslides 2021: At least 30 people died in Mumbai suburbs after several houses collapsed when heavy rain triggered landslides.
• Environmental Impact: Landslides result in habitat destruction, soil erosion, and water pollution, altering ecosystems and jeopardizing biodiversity. The soil displacement contributes to increased erosion, negatively impacting water quality and aquatic life. 

Way Forward 

• Landslide Monitoring involves deploying sensors, satellite imagery, and ground-based instruments to detect ground movement and potential landslide precursors. 
  • For this, the National Highways Authority of India (NHAI) is planning to install a landslip detection system on the Gap Road stretch of the Kochi-Dhanushkodi National Highway in Munnar to warn the authorities about landslips. 
  • Landslip Detection System: It was developed by the Indian Institute Of Technology-Mandi (IIT-Mandi), the Indian Army, and the Defence Research and Development Organisation (DRDO). 
• Generation of User-Friendly Landslide Hazard Maps: It covers aspects of reliability and validation of landslide zoning maps in Indian scenarios and landslide zoning by making use of advanced tools such as Unmanned Aerial Vehicles (UAV), Terrestrial Laser Scanners, and very high-resolution Earth Observation (EO) data. 
• Following International Best Practices: Brazil’s SNAKE System: The SNAKE System is the Landslide Early Warning System (LEWS), epitomizing advancements in digital monitoring, forecasting, and alert mechanisms. 
• Creation of a Special Purpose Vehicle (SPV) for Landslide Management: An expert professional group should be constituted at the national level to 
  • Study and decide on risk mitigation strategy for landslides. 
  • To recommend permanent fixing of the identified landslide hotspots. 
• Awareness Programmes: They aim towards a culture of awareness generation and preparedness so that people in society become alert and aware in case of an emergency or take preventive measures before disaster strikes. 

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