Shallow landslide hazard assessment in the Camburi river catchment, São Sebastião municipality – SP

Abstract

: In February 2023, the São Sebastião municipality (São Paulo State, Brazil) was hit by an extreme rainfall event that triggered hundreds of shallow landslides on the Serra do Mar slopes, outlining the necessity for detailed landslide hazard cartography. This research aims to quantitatively assess the hazard posed by landslides to the exposed elements of the Camburi river basin, located in São Sebastião. Susceptibility was evaluated through the SHALSTAB model, achieving good results (sensitivity = 0,865, specificity = 0,457, and F1-score = 0,720), allowing to identify unstable areas associated with rainfall thresholds up to 50mm/day. Hazard was assessed using the Gravitational Process Path (GPP) model, with reasonable accuracy for the final coupled model (ROC-AUC = 0,720). Approximatively 69% of the basin was classified as low and very low hazard areas, with 8% associated with high and very high hazard zones. We were able to identify buildings located in areas classified as both unstable and in the landslide runout zones, highlighting the coupling between irregular land tenure and geomorphological risk.