Probabilistic Rainfall Thresholds for Shallow Landslides Initiation – A Case Study from the Nilgiris District, Western Ghats, India

Rainfall is one of the major causes of landslides/landslips across the globe. The fatalities and damage caused by rainfall induced landslides increased in recent days. The Nilgiris district in Western Ghats part of Tamil Nadu state is one of the very high to severe landslide hazard-prone areas of India.  The present study is focused on estimation of rainfall thresholds and the temporal probability of landslides in different landslide-prone slopes in part of The Nilgiris district. The landslide prone areas identified in earlier research are used for the present study.  The landslide locations data for the years 1824 to 2018 were collected and a spatial database on landslide inventory was created. A detailed inventory carried out on the 2009 landslides were analysed and used for the calculation of rainfall thresholds. Monthly and Yearly Rainfall data for the years 2000 to 2011 were collected for 37 rainguage stations from various government agencies. Based on the quality and quantity of data, the rainfall thresholds for 14 different locations were estimated viz., Aderly, Coonoor, Coonoor Railway, Governor Sola, Ooty (Near Botanical Garden), Runnymedu, Burliar where the probability of landslide occurrences is high.  The temporal probability of landslide was calculated for four years viz., 1, 3, 5 and 10 years. The present study can be used as a key to develop an early warning system in The Nilgiris District.