Community-scale slope stability assessment of urbanisation scenarios in North Quito, Ecuador.

Quito is home to nearly three million inhabitants, many of whom live in informal settlements on the steep soil-mantled slopes that surround the city. Within Quito's multi-hazard environment, the combination of rapid urban expansion onto already landslide-prone slopes-often without adequate urban planning or provision of services-and rainfall associated with the subtropical highland climate, generates a risk to life and infrastructure from landslides. Landslide hazard assessment and mitigation is challenging due to the large area involved, complexity of urban slopes and sparsity of data. In this study, conceptual models of characteristic slope geometries, soil properties and urban features are developed based on three landslide-prone communities in North Quito. These models form the basis for investigating different urbanisation scenarios and the slope stability response to simulated rainfall. They are used to configure the physics-based Combined Hydrology And Stability Model, CHASM, which is run stochastically allowing tens-of-thousands of combinations of slope input factors to be investigated. Analysis of simulation data includes regional sensitivity analysis and the identification of different rainfall-intensity thresholds for triggering landslides. Slope cutting is identified as the primary driver of small-scale urban landslides. Analysis of simulated landslide characteristics allows the trigger mechanisms for different scenarios to be hypothesised and shows a close correlation with the ratio of strata thickness to effective apparent cohesion. These results support revegetation within existing informal communities, and the preservation of existing vegetation and careful design of cut slopes in new settlements. Supplementary Information: The online version contains supplementary material available at 10.1007/s10346-025-02608-6.