Statistical analysis of morphometric variables for basins associated with debris flow events in Colombia: a comparison within types of flows and with non-susceptible basins

The occurrence of debris flows¹ in mountainous basins is a major risk in the Andean region of Colombia. Characterization of those debris-flow-prone basins and comparison with other mountainous areas that are not susceptible to the occurrence of debris flows is a significant step towards susceptibility analyses. Usually, the attention is focused on a particular event or a rather reduced set of events observed at a particular location, whereas a more general, thorough understanding is not typically addressed. Morphometric parameters and rainfall variables were used in this article to describe some of those watersheds in Colombia, the calculation of 25 variables for 151 basins associated with actual debris flows events and 54 non-susceptible basins was meant to describe different aspects of each basin, specifically: geometry, drainage conditions, hypsometry, rainfall and slope. A statistical examination, including an analysis of variance (ANOVA) and a principal component analysis (PCA), is presented and discussed. Results suggest that some variables can be used to distinguish between basins that exhibit different type of flows (i.e. mud-flows, debris flows and hyper-concentrated flows) while others can potentially separate the non-susceptible basins from the susceptible ones, besides, PCA results grouped naturally into categories representing the different aspects mentioned above. However, morphometric variables were found not sufficient to fully differentiate the occurrence of different types of flows nor discriminate between susceptible and non-susceptible basins. This analysis can be used to calculate indicators that account for the debris flow susceptibility, as it can be associated with weights for assessing the relative importance of all the different aspects of the basins’ characterization.