**6. Conclusions**

The occurrence of the debris flows in Montecito in 2018 were not a surprise, but the magnitude and impacts of the flows were. Before the rains arrived, first responders were prepositioned, evacuations were implemented, a proclamation of emergency was executed at local scales and the operations center was staffed. However, despite technical or engineering advances, such sudden events occurred after extreme fires, and the susceptibility as thresholds indicating their probable occurrence could not be adapted to this remarkable situation. In addition, the Montecito event highlighted the need to develop more refined models that can be used in the field to accurately identify the risk and map debris flow inundation zones. Being able to map the hazard and

related risk help convey this critical information to decision makers to implement mitigations and appropriate emergency measures, such as issuing an evacuation alert. Decision makers need to have confidence and be able to point to the science that what they are doing is proper and prudent. On the other hand, the studied catchments were investigated as a new example to detect a possible "cauliflower effect," and these new results confirm the influence of morphological conditions playing a key role in real postfire debris flow events. In the era of extremes, intense rainfall intensities are expected (at daily and not annual scales) but coupled with severe dry periods and severe fires, runoff concentration and violent hydrological responses could occur and surprise many people located at the outlet of small catchment. Thus, even if RuiCells© model should be more calibrated, we propose to assess such risk considering that catchments are totally burned, and the detection of "cauliflower effects" is finally not so theoretical. And to follow this study, we plan to measure this effect on the other postfire debris flows that occurred in California, with a set of 334 events of events.
