Causal analysis of unprecedented landslides during July 2021 in the Western Ghats of Maharashtra, India.

The occurrence of landslides is not uncommon in the Western Ghats of Maharashtra, India. However, during the last week of July 2021, an unprecedented number of landslides due to heavy rainfall were reported in this region. To determine the cause of the large-scale landsliding, we mapped an event-based landslide inventory using high-resolution satellite imagery and identified 5012 landslides. We analysed rainfall data for the 2005–2021 period to identify the anomaly in rainfall quantity and its distribution which triggered such large number of landslides, particularly in 2021, even though heavy annual monsoonal rainfall is observed every year in this region. It is observed that the quantity of rainfall in 2021 is much lesser than that seen in most of the previous years. Analysis of antecedent rainfall for time-stamped landslides, such as Jui (2005), Malin (2014) and Taliye (2021), shows that two-day antecedent rainfall is the primary trigger of landslides in the region. An in-depth comparison of rainfall variability for all the years which recorded more rainfall than 2021 shows that the amount of two-day consecutive rainfall is significantly higher in 2021, although the cumulative seasonal rainfall is less than in preceding years. Further, this anomalously high rainfall was concentrated around the 600 m – 900 m elevation range. The probable consequence of such spatiotemporally localised heavy rainfall over higher elevations was rapid soil saturation triggering a large number of landslides in 2021. In times when the effect of climate change is visible in the form of weather extremes, the present study may aid in preparedness for response to such disasters. [ABSTRACT FROM AUTHOR]