Deadly disasters in southeastern South America: flash floods andlandslides of February 2022 in Petropolis, Rio de Janeiro

On 15 February 2022, the city of Petropolis in the highlands of the state of Rio de Janeiro, Brazil, received an unusually high volume of rain within 3 h (258 mm), generated by a strongly invigorated mesoscale convective system. It resulted in flash floods and subsequent landslides that caused the deadliest landslide disaster recorded in Petropolis, with 231 fatalities. In this paper, we analyzed the root causes and the key triggering factors of this landslide disaster by assessing the spatial relationship of landslide occurrence with various environmental factors. Rainfall data were retrieved from 1977 to 2022 (a combination of ground weather stations and the Climate Hazards Group InfraRed Precipitation - CHIRPS). Remotely sensed data were used to map the landslide scars, soil moisture, terrain attributes, lineof-sight displacement (land surface deformation), and urban sprawling (1985-2020). The results showed that the average monthly rainfall for February 2022 was 200 mm, the heaviest recorded in Petropolis since 1932. Heavy rainfall was also recorded mostly in regions where the landslide occurred, according to analyses of the rainfall spatial distribution. As for terrain, 23% of slopes between 45-60ffi had landslide occurrences and east-facing slopes appeared to be the most con- ducive for landslides as they recorded landslide occurrences of about 9% to 11 %. Regarding the soil moisture, higher variability was found in the lower altitude (842 m) where the residential area is concentrated. Based on our land deformation assessment, the area is geologically stable, and the landslide occurred only in the thin layer at the surface. Out of the 1700 buildings found in the region of interest, 1021 are on the slope between 20 to 45 degrees and about 60 houses were directly affected by the landslides. As such, we conclude that the heavy rainfall was not the only cause responsible for the catastrophic event of 15 February 2022; a combination of unplanned urban growth on slopes between 45-60 degrees, removal of vegetation, and the absence of inspection were also expressive driving forces of this disaster.