KOCHI: Isro‘s Landslide Atlas of India-2023, which includes landslide exposure analysis carried out in mountainous areas, has placed 13 of Kerala’s 14 districts among the top 50 vulnerable regions in the country.
The Atlas ranks 147 landslide-prone districts in 17 states and two Union Territories according to the highest landslide density and highest population exposure.The Northwest Himalayas witness 66.5% of landslides in India, followed by the Northeast Himalayas (18.8%) and the Western Ghats (14.7%). The districts have been ranked for their exposure to landslides in terms of socio-economic parameters.
Based on exposure to landslides, Wayanad is placed 13th in the Atlas. Thrissur district of the state in ranked 3, Palakkad 5, Malappuram 7, Kozhikode 10, Ernakulam 15, Idukki 18, Kottayam 24, Kannur 26, Thiruvananthapuram 28, Pathanamthitta 33, Kasaragod 44 and Kollam 48. The 14th district, Alappuzha, also figures on the list, at 138th place. The database includes three types of landslide inventory – seasonal, event-based and route-wise – for the 1998-2022 period.
Seasonal inventory contains a pan-India landslide database corresponding to the 2014 and 2017 rainy season in India. Event-based inventory contains details of some of the major triggering events, such as Kedarnath (2013) and Kerala (2018) floods, Sikkim earthquake (2011) as well as a few large valley blocking landslides.
Route-wise inventory contains details of landslides along selected routes of tourist and pilgrimage importance.
The event-based inventory from 2000-2021 says that Kerala saw a total of 6,039 events – 5,191 in 2018, 756 in 2019, 9 in 2020 and 29 in 2021. In the 2014 and 2017 monsoon seasons, there were 9 and 45 landslides, respectively.
The Atlas states that rainfall threshold for landslides is the value which, when reached or exceeded, is likely to trigger landslides. Rainfall thresholding for slope failure can be established using process-based, empirical or statistical approaches, it says. Historical data on landslide-causing rainfall events and the corresponding landslide records can be used to establish rainfall thresholds.
It states that vulnerability of inhabitants and households is more significant in the Western Ghats due to the very high population and household density, especially in Kerala, even when fewer landslides exist than in the Himalayan regions. The steep escarpments of the Western Ghats record occurrences of landslides, but these are primarily controlled by the soil cover on the slopes.