Using data to reduce subjectivity in landslide susceptibility mapping
In recent years, numerous landslides on hillsides in urban and rural areas have underscored that understanding and predicting these phenomena is more than an academic curiosity—it is a human necessity. When unstable slopes give way after intense rainfall, the consequences can be devastating, with both human and material losses. These recurring tragedies led us to a simple yet powerful question: Can we build landslide susceptibility maps that are more objective, transparent, and useful for local authorities and residents?
The answer led us to compare two susceptibility analysis methods: the traditional Analytical Hierarchy Process (AHP) and its statistical version, the Gaussian AHP. After months of multidisciplinary work, we found that the Gaussian AHP, which relies on data rather than subjective judgments, better identifies critical areas in a more balanced manner and is consistent with the landslide patterns observed in the field. We share here our journey and the lessons we learned. Our findings are published in Scientific Reports.
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We chose the municipality of São Sebastião, on the north coast of São Paulo, Brazil, as a case study because official surveys indicate it is among the most vulnerable cities in the country. There, mountainous relief, escarpments, and urban occupation of slopes create a high-risk context. We selected 16 conditioning variables (e.g., slope, relative slope position, terrain ruggedness, soil type, and distance to rivers and roads) and collected high-resolution data from satellites, digital terrain models, and landslide inventories.
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If you live in a mountainous region, work in urban management, or simply care about extreme events, understanding how we build susceptibility maps can save lives. The landslides in São Sebastião showed that the combination of intense rainfall (accumulations of up to 683 mm in 24 hours) and disorderly occupation creates a perfect storm. Using more objective methods, such as the Gaussian AHP, we can provide civil defense and urban planners with a more precise tool for identifying critical areas and guiding evacuations, drainage projects, and land-use policies.
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