**3. Data**

Data from a total of 347 landslides which occurred from 2014 to 2018 were collected from Border Road Organization, Government of India under Project DANTAK (Figure 1b). The data included the dates and geographic coordinates of landslide location based on field observations, interactions with locals, and media reports. The types of movement in the region based on Cruden and Varnes' [37] classification are: debris slides, rock falls, earth flows, and rotational landslides. The field visit conducted in November 2017 revealed the landslides to be shallow, with depths ranging up to few meters, and able to be mapped as single points. The yearly distribution (Figure 3a) of landslides shows that the majority of the landslides occurred in 2017 and 2018, whereas the monthly distribution (Figure 3b) shows that 89% of landslides occurred between the months of June and September. It is often difficult to determine the rainfall conditions responsible for failures, due to lack of rain gauge

density and high distances between rain gauges and landslide points [26,38]. As multiple landslides can occur during a rainfall event, subsequent landslides for a single rainfall event after the initial failure were not considered for the threshold analysis. Thus, in this study, we defined a landslide event as "single landslide-triggering event", in which the landslide events after the initial failure were not considered for threshold estimation [16,26]. A rainfall event was defined as a period of continuous rainfall separated by dry (without rainfall) period. Using all these criteria, the total numbers of rainfall and landslide events during the threshold determination time frame (2014–2017) were 477 and 104, respectively. The zones were divided based on spatial coverage of rain gauges [4,26]. A buffer radius of 15 km around each rain gauge was selected to divide the region into zones. In terms of landslide events for respective zones, half of the landslide events occurred in Zone 2 (49) followed by Zone 3 (40) and Zone 1 (15).

**Figure 3.** Number of landslides (**a**) per year and (**b**) per month between 2014 and 2018.

The daily rainfall data used for this study (Figure 4) was collected from two rain gauges at Deothang and Kanglung, managed by the National Centre for Hydrology and Meteorology, Bhutan (http://www.hydromet.gov.bt). The average cumulative yearly rainfalls for Deothang and Kanglung for 2014–2018 were 3495 mm and 1020 mm, respectively, of which 89% occurred during the monsoon season (June–September). The higher precipitation observed in Deothang is due to its location on the windward side of the mountain.

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**Figure 4.** Average monthly rainfall in the study region for both rain gauges (2014–2018).
