Spatial distribution, temporal trends and impact of landslides on Sao Miguel Island from 1900 to 2020 based on an analysis of the Azores historical natural hazards database

Landslides are the most frequent type of natural hazard in the Azores archipelago, primarily due to the volcanic nature and geomorphologic features of the islands. The NATHA (Natural Hazards in Azores) database is a repository of documents reporting those natural disaster events that have occurred on the Azores since their settlement in the mid-fifteenth century. This work presents and explores the landslide events that have occurred on Sao Miguel Island in the period 1900-2020. A total of 236 landslide events were catalogued. The temporal distribution of the landslide events reveals a higher concentration of events after 1996, which is related to a change in the rainfall regime but also to the increasing dissemination of information. The influence of climate change on landslide occurrence is demonstrated for the first time in the Azores. The landslide events catalogued in the NATHA database were responsible for 82 fatalities, 41 injuries and 305 people made homeless, while 66 buildings were partially or completely destroyed. The spatial distribution of landslide events shows that Povoacao is the municipality most prone to landslide occurrence as well as to landslide impact. Rainfall was the triggering factor of most landslide events (70%) on Sao Miguel Island, and landslide events have been most frequent during the wettest months of the year from November to March. The obtained results demonstrate the need of landslides prevention and preparedness programs in specific areas of Sao Miguel Island.