**Abstract**

Most of the studies focused on triggering conditions to identify the critical thresholds beyond which the occurrence of postfire debris flows becomes more than likely. However, researchers rarely focused on the relations between the morphological patterns and influences on surface water flows, while after extreme fires, the burned areas strongly reduce the infiltration capacities and generate important runoffs. So, to address these relations, we used the cellular automaton RuiCells©. This model brings out the concentration areas inside a given form, in which networks and surfaces are well-structured, and patterns are similar to efficient forms that can be found by looking at a cauliflower. This model has been applied to assess the flash floods susceptibility in sedimentary areas, with a success rate of 43%, so we decided to apply this model to the five catchments located at the apex of urbanized fans upstream of Montecito (Santa Barbara County, USA), affected by debris flows that occurred on January 9, 2018, 20 days after the Thomas Fire (one of the largest wildfires in California history). Some of values have never been observed elsewhere. So, we might apply this approach to assess the postfire debris flows susceptibilities given the increasing number of fires and mega fires.

**Keywords:** debris-flows, postfire conditions, spatial behavior, Montecito, cauliflower effect
