Performance and sensitivity analysis of the Morpho2DH model in extreme events in southern Brazil

Debris flows are a mixture of water and sediment with a continuous fluid behavior driven mainly by gravity. Computational modeling can be used to predict areas susceptible to these phenomena. When using computational modeling, sensitivity analysis is a crucial step to evaluate and interpret the model results. Thus, the objective of this study was to evaluate the performance of the Morpho2DH debris flow model, perform a sensitivity analysis of its input parameters, recommend application criteria, and increase the use of such a model in South America and Brazil. The model was applied in two representative areas with occurrences of debris flows in southern Brazil. The methodology consisted of two steps: (i) model calibration; (ii) one-at-a-time (OAT) sensitivity analysis (SA) for selected input parameters. The sensitivities of input parameters were evaluated for total area affected, distance traveled, mean velocity, and deposited volume. The results of the SA demonstrate that the most sensitive parameters were maximum bed erosion depth, resistance coefficient, minimum flow depth, and mean particle diameter. Meanwhile, static bed sediment concentration, vegetation, and internal friction angle showed moderate sensitivity. Parameters such as liquid density, sediment concentration, and sediment density showed the lowest sensitivities. Finally, it is recommended to use the model for situations where input volume and terrain data (mainly the erosion thicknesses or soil depth) are well-defined. Additionally, the computational cost of this model should be considered, concerning the magnitude of the event to be simulated.