Recommended citation: Stojanovic, M., Sori, R; Vazquez, M., Pérez-Alarcón, A., Ernst, J., Nieto, R., Gimeno, L. (2024). The extreme flood event of October 22 - November 8, 2006 over the Iberian Peninsula: Associated mechanisms. MedGU Annual Meeting. Barcelona, Spain, 25-28 November 2024.

Abstract

Floods are complex phenomena that can originate from different causes and are considered one of the most damaging for the infrastructures, economy, ecosystems, and even causing human loss. Those originating from heavy rainfall are expected to in-crease in the future as precipitation intensifies in some regions. This is why multiple studies have investigated and are currently investigating the mechanisms that cause and modulate the occurrence of floods. In this study, we perform an assessment of the flood event induced by heavy precipitation that affected the Iberian Peninsula (IP) from October 22, 2006 to November 8, 2006, which caused considerable infrastructure damage and human fatalities. According to the global flood database of the Dartmouth Flood Observatory, it was the longest flood event (18 days) that affected the IP during the 1999-2021 period. The objective was to investigate the mechanisms that induced heavy rainfall over the IP causing the flood. To do it were determined the sources of moisture for precipitation during the event through the Lagrangian model FLEXPART. This model permitted to track backward in time the parcels and air masses that lost humidity and caused the heavy rainfall, allowing to identify those regions from where air masses uptake before precipitating, considered as sources of moisture. The results show that this event was triggered by the influence of the extratropical storm located over the northeastern Atlantic, which imposed intense southeast zonal flow anomalies brining moisture that favored the occurrence of heavy rainfall during various days. The principal moisture sources were identified in the subtropical Atlantic Ocean to the southeast of the IP. In addition, over the IP prevailed the convergence of the vertically integrated moisture flux and intense rainfall, leading to strong positive anomalies of the soil moisture, principally in the central region of Portugal and central west Spain. The soil water content during previous days favored the saturation and the later onset of the flood. This study is the beginning of a more extensive work plan for the attribution of the occurrence of floods due to heavy rains in the IP, and for the development of knowledge about these phenomena.