Reconstruction of Torrential Activity in Cerradillas Valley (Sierra de Guadarrama National Park, Spain) Using Dendrogeomorphic Techniques

Flash floods in Mediterranean mountain catchments are a significant natural hazard, but systematic historical records of their occurrence are often lacking. This study reconstructs the history of torrential activity in the previously unexplored Arroyo Cerradillas catchment in the Sierra de Guadarrama, Spain, to better understand the event frequency and its triggers. The main methods involved dendrogeomorphological analysis of growth disturbances in Scots pine (Pinus sylvestris L.) trees. Torrential events were dated and their intensity assessed by identifying and cross-dating scars, reaction wood, and abrupt changes in growth, which were integrated into a weighted index. The results yielded a chronology of 12 significant torrential events between 1935 and 2003. This record shows strong coherence with regional studies but also highlights the localized nature of some floods, and it adds two previously undocumented event years (1998 and 2003) to the regional chronology. The 1996 event was identified as having exceptional magnitude. This study confirms the value of dendrogeomorphology for completing historical flood records and improving hazard assessments. The intense signal from 1996 was likely caused by widespread mechanical damage from snow and wind rather than a direct hydrological flood, demonstrating the complexity of interpreting geomorphic processes in mountain environments.