CHENNAI: The latest mapping done by the Geological Survey of India (GSI) of all landslide-prone areas across India has shown that about 1,000 sq km of area in Tamil Nadu, mostly Nilgiris, faces high risk. A total of 11,000 sq km (in TN) was mapped, of which 8,000 sq km falls in low-risk category, 2,000 sq km in moderate and 1,000 in high-risk category based on their landslide susceptibility status, according to a submission by the Ministry of Earth Sciences made in Parliament.
The Nilgiris district has been identified in particular as one of the key landslide-prone regions in India. The data presented were based on the mapping done by GSI of all the 4.3 lakh sq km of landslide-prone hilly and mountainous areas, spread across 19 states and UTs.
This included the Himalayas, the north-eastern hill belts and the Western Ghats. The GSI has also started issuing experimental early warning bulletins to states, the information presented as part of a reply by Union Minister of State (Independent Charge) for Science and Technology and Earth Sciences Jitendra Singh said.
While the GSI initially completed the susceptibility mapping on a 1:50,000 scale across 4.3 lakh sq km, it also subsequently carried out a more advanced meso-scale mapping (scale of 1:10,000/1:5,000), focussing on 200 critical sectors identified in consultation with state governments. Of these, GSI has completed work in 160 such sectors by the end of 2024-25 which serve as vital inputs for infrastructure planning, zoning regulations and community safety in fragile hill regions.
Since this year’s monsoon season, based on a prototype of a regional Landslide Early Warning System developed for India, GSI has been providing operational and experimental landslide forecast bulletins for 21 districts in eight states. Nilgiris is the only TN district in the list. Others are from WB, Sikkim, Kerala, Karnataka, Uttarakhand, HP and Nagaland.
Nationally, the susceptibility mapping reveals key variations across states. Uttarakhand, AP, HP, Nagaland and parts of Western Ghats such as Kerala and Maharashtra show a relatively high proportion of land in “high” risk category, whereas places in states like Assam, Tripura and Meghalaya mostly fell under low risk.
The reply also highlighted post-disaster landslide studies and detailed site-specific landslide investigations on 1:1,000/2,000 scale done by GSI to suggest remedial measures for landslides and unstable slopes. During 2019-2024, GSI had carried out 45 such detailed site-specific investigations.