Hydrogeomorphological analysis and modelling for a comprehensive understanding of flash-flood damage processes: the 9 October 2018 event in northeastern Mallorca

[EN] A flash-flood event hit the northeastern part of Mallorca on 9 October 2018, causing 13 casualties. Mal- lorca is prone to catastrophic
flash floods acting on a sce- nario of deep landscape transformation caused by Mediter- ranean tourist resorts. As global change may exacerbate dev- astating flash floods, analyses of catastrophic events are cru- cial to support effective prevention and mitigation measures. Field-based remote-sensing and modelling techniques were used in this study to evaluate rainfall¿runoff processes at the catchment scale linked to hydrological modelling. Continu- ous streamflow monitoring data revealed a peak discharge of 442 m³ s¿¹ with an unprecedented runoff response. This ex- ceptional behaviour triggered the natural disaster as a com- bination of heavy rainfall (249 mm in 10 h), karstic features and land cover disturbances in the Begura de Salma River catchment (23 km²). Topography-based connectivity indices and geomorphic change detection were used as rapid post- catastrophe decision-making tools, playing a key role dur- ing the rescue search. These hydrogeomorphological preci- sion techniques were combined with the Copernicus Emer- gency Management Service and ¿ground-based¿ damage as- sessment, which showed very accurately the damage-driving factors in the village of Sant Llorenç des Cardassar. The main challenges in the future are to readapt hydrological modelling to global change scenarios, implement an early flash-flood warning system and take adaptive and resilient measures on the catchment scale.