Constructing a complete landslide inventory dataset for the 2018 Monsoon disaster in Kerala, India, for land use change analysis

Abstract

Abstract. Event-based landslide inventories are important for analyzing the relationship between the intensity of the trigger (e.g. rainfall, earthquake) and the density of the landslides in a particular area, as a basis for the estimation of the landslide probability and the conversion of susceptibility maps into hazard maps required for risk assessment. They are also crucial for the establishment of local rainfall thresholds that are the basis of Early Warning Systems, and for evaluating which land use/land cover changes are related to landslide occurrence. The completeness and accuracy of event-based landslide inventories are crucial aspects to derive at reliable results or the above types of analysis. In this study we generated a relatively complete landslide inventory for the 2018 Monsoon landslide event in the state of Kerala, India, based on two inventories that were generated using different methods: one based on Object Based Image Analysis (OBIA) and the other on field surveys of damaging landslides. We used a collaborative mapping approach based on the visual interpretation of pre-and post-event high-resolution satellite images available in Google Earth, adjusted the two inventories and digitize landslides that were missed in the two inventories. The reconstructed landslide inventory database contains 4728 landslides consisting of 2477 landslides mapped by OBIA method, 973 landslides mapped by field survey, 422 landslides mapped both by OBIA and field method and an additional 856 landslides mapped using the visual image (GE) interpretation. The dataset is available at https://doi.org/10.17026/dans-x6c-y7x2 (van Westen, 2020). Also, the location of the landslides was adjusted, based on the image interpretation, and the initiation points were used to evaluate the land use/land cover changes as a causal factor for the 2018 Monsoon landslides. A total of 45 % of the landslides that damaged buildings occurred due to cut-slope failure while 34 % of those impacting on roads were due to road cut-slope failures. The resulting landslide inventory is made available for further studies.

Mechanisms of Initiation, Runout, and Rainfall Thresholds of Extreme-Precipitation-Induced Debris Flows

“…From these observations, if this multitude increase in threshold prevails, efforts should be made to analyze its causes and implications. The number of debris flows within the Idukki district also increased compared to previous years (Hao et al 2020). (Yunus et al 2021).…”

“…We find previously established thresholds in the Idukki district are unsuitable to predict debris flows triggered by high-intensity, short-duration rainfall. in all 12 out of 13 landslide-prone districts except Idukki (Hao et al 2020). Hao et al (2020) identify a total of 2816 debris flows, 1760 shallow slides, and 152 rockfalls that occurred in 2018.…”

“…in all 12 out of 13 landslide-prone districts except Idukki (Hao et al 2020). Hao et al (2020) identify a total of 2816 debris flows, 1760 shallow slides, and 152 rockfalls that occurred in 2018. These will cause huge implications in soil productivity as more and more sediments are transported to the river every year and subsequently will affect the ecosystem (Yunus et al 2021).…”

“…Though landslides were common in the past, their numbers increased significantly during 2018, 2019, and 2020 (Abraham et al 2019, Achu et al 2020, Sajinkumar et al 2014, Sajinkumar & Anbazhagan 2015. For example, in the Idukki district, 64 major landslides occurred until 2010, whose total count rose to 2223 in 2018 (Hao et al 2020, Kuriakose et al 2010, Kuriakose, Sankar & Muraleedharan 2009. In addition to the threat to life, debris flows disrupt livelihood and socio-economic activities in mountainous regions, leading to mass population displacements (Jakob et al 2005, Dowling & Santi 2014, Ding et al 2016.…”

“…Mountainous regions in Japan, China, and India have witnessed series of debris flows in the last decade (Furuichi et al 2018. Examples are the decade-long occurrence of debris flows post the Great Wenchuan earthquake in China (2008China ( -2020; the 2016 typhoon Lionrock triggered debris flows in Hokkaido, Japan; and the 2018 extreme-precipitationinduced debris flows in Kerala, India (Zhu et al 2020, Hao et al 2020, Dai et al 2021. Extreme precipitation during 2018, 2019, and 2020 monsoons induced series of catastrophes, i.e., flash floods, landslides, and debris flows in the Western Ghats, India, resulting in more than 500 casualties and affected over 5.4 million people in 1200 towns (Mishra & Shah 2018, Ramasamy et al 2019, Sankar 2018, Ramasamy et al 2019, Vishnu et al 2019.…”