Flood Variability during the Last Millennium in Northern Iberia: A View from Spanish Lake Records

Extreme flood events and related disasters are becoming an increased economic and social concern in the context of global environmental change. Therefore, accurate assessment of the effects of climate change on flood occurrence and magnitude in time and space is of paramount relevance for society. This is particularly relevant in sensitive areas such as South-western Europe where both Atlantic and Mediterranean climate patterns interact dynamically at variable temporal and spatial scales. However, climate change impacts on flooding are difficult to recognize partly due to geographically sparse flood records and the shortness of the instrumental datasets. Detection of temporal changes on local and regional flooding therefore requires long-term records to overcome these limitations. A valuable approach to reconstruct long-term, continuous flood archives is studying lake sedimentary records. This allows investigating the long-term dynamic of extreme events at decadal to centennial time scales. In this context, we have investigated four lacustrine sedimentary archives with robust age models located along an E-W transect in Northern Spain (Sanabria, Arreo, Marboré and Montcortès) that provided the needed time perspective to assess the effects of climate variability and land use change on flood frequency and intensity in this region during the last millennium. Paleoflood records from NW Spain (Sanabria and Arreo) and the Central Pyrenees (Marboré) showed an abrupt increase in extreme events since the 17th century. On the other hand, Lake Montcortès (NE Spain) sedimentary sequence recorded more extreme floods during the Late Middle Ages and the 19th century. A see-saw pattern in flood frequency seems to occur during the MCA/LIA transition with more (less) flood events occurring during cold (warm) phases in Atlantic and Mediterranean areas respectively. This study highlights how paleoflood records from lake sediments provide an innovative approach to better understand long-term flood hydrology. This project has received funding from the European Union¿s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement Nº 796752 (FLOODARC)