Climate snow-avalanche linkage revealed by geomorphological, historical and tree-ring records in the central Spanish Pyrenees

Snow avalanches are significant natural hazards in mountainous regions, and their frequency and magnitude are increasingly influenced by changing climatic conditions. This study presents a multi-proxy reconstruction of snow avalanche activity over the past century (1910–2014 CE) in the Canfranc Valley, Central Spanish Pyrenees. The reconstruction integrates geomorphic mapping, dendrochronology, historical archives, and climatic data. A total of 345 trees were sampled and analysed, yielding 1322 growth disturbances (GD), which enabled the reconstruction of 30 and 27 avalanche events in the Estiviellas (ES) and Rinconada (RI) paths, respectively. The analysis was complemented by geomorphological assessments based on high-resolution LiDAR-derived terrain models, along with historical records and fieldwork validation. Also, avalanche size was estimated using a bivariate statistical model based on runout distance and width, both inferred from the most distal affected trees. These size proxies, combined with return period analyses, indicate that the largest avalanches (e.g., 1962, 1986, 1993) occurred more frequently in the second half of the 20th century, while recent decades have been characterized by smaller but more frequent events, typically confined to upper slopes. Structural Equation Modelling (SEM) was applied to examine the relationships between reconstructed avalanche activity, snowpack, climate variables, and atmospheric circulation anomalies. Results show that negative phases of the North Atlantic Oscillation (NAO) enhance precipitation and lower temperatures, thereby increasing snowpack depth and avalanche probability. Snowpack emerged as the principal mediator between meteorological variables and avalanche activity. Although long-term trends indicate increasing temperatures and precipitation, their direct influence on avalanche size was limited. These findings underscore the non-linear and threshold-dependent nature of avalanche dynamics and highlight the critical role of snowpack and regional climate variability. The observed decline in avalanche size and the shift toward smaller, more frequent events may reflect broader cryospheric transformations under warming conditions. This study provides valuable insights for risk assessment and the development of adaptive hazard management strategies in mountain environments affected by climate change.