Why Kerala is particularly vulnerable to landslides

Why in the News?

Fresh landslides in Kerala, following the earlier Wayanad disaster, have renewed attention on why the state is so slide-prone. The explanation separates the terrain and soil conditions that make slopes unstable from the rainfall events that actually trigger a slide.

What is the difference between conditioning and triggering factors?

1. Conditioning factors: These are the standing features that make a slope prone to failure, such as steep gradients, weathered soil and geology. A steep gradient is a slope angle that has a high incline or is very vertical, making the ground less stable and more likely to slide or fall down.
2. Triggering factors: These are the immediate events that set off a slide, above all intense or prolonged rainfall.
3. Combined effect: A slope must be both predisposed by conditioning factors and hit by a trigger for a landslide to occur.

Why is Kerala especially vulnerable?

1. Western Ghats terrain: Steep slopes of the Western Ghats provide the gradient that makes failure possible.
2. Weathered soil: Deeply weathered, loose soil on these slopes loses cohesion when saturated.
3. Extreme rainfall: Short bursts of very heavy rain, worsened by climate change, act as frequent triggers.

How is landslide risk being mapped?

1. Landslide Atlas: The ISRO National Remote Sensing Centre’s Landslide Atlas (1998-2022) maps slide-prone zones across India.
2. Hazard zonation: Such mapping identifies high-risk areas for planning and early warning.
3. Planning use: Zonation data can guide construction limits and evacuation planning in vulnerable districts.

Conclusion

Kerala’s landslides result from predisposing terrain and soil combined with increasingly extreme rainfall triggers. Distinguishing conditioning from triggering factors clarifies where and when slides occur. Hazard zonation using the ISRO Landslide Atlas is the basis for prevention and early warning.

Back2Basics

National Landslide Risk Management Strategy (NLRMS), 2019 (NDMA)

The National Landslide Risk Management Strategy (2019), prepared by the National Disaster Management Authority (NDMA), is India’s first comprehensive framework for reducing landslide risk through prevention, preparedness, mitigation, and capacity building.

Key Pillars

1. Hazard Mapping: Prepare national and state-level Landslide Hazard Zonation (LHZ) maps; Identify and monitor vulnerable slopes.
2. Monitoring & Early Warning: Install rainfall- and ground movement-based monitoring systems; Develop Landslide Early Warning Systems (LEWS).
3. Mitigation Measure: Slope stabilization, retaining walls, rock bolting, drainage improvement, and bio-engineering; Afforestation and regulated hill cutting.
4. Land-use Planning: Restrict construction, quarrying, and infrastructure projects in high-risk zones; Integrate hazard maps into master plans.
5. Capacity Building: Train local authorities, engineers, and communities; Conduct awareness campaigns and mock drills.
6. Emergency Response: Strengthen search-and-rescue, evacuation plans, and post-landslide recovery.
7. Research & Technology: Use GIS, Remote Sensing, LiDAR, drones, and satellite monitoring for landslide assessment; Promote research on landslide prediction and climate impacts.

PYQ Relevance

[UPSC 2021] Differentiate the causes of landslides in the Himalayan region and Western Ghats.

Linkage: The PYQ focuses on the causes and mitigation of landslides and slope instability. It explains how steep gradients increase slope failure risk and the need for scientific slope management.