Periodic Reporting for period 1 - FLOODARC (Understanding long-term FLOOD pattern variability in Western Mediterranean using natural ARChives) Reporting period: 2019-04-01 to 2021-03-31 Summary of the context and overall objectives of the project Floods affect more people worldwide than any other natural hazard. Society is becoming even more vulnerable to river flooding because of increasing populations and exposure of infrastructure. One of the greatest challenges in climate science is understanding the effects of climate variability on the spatial and temporal variability of floods. Unfortunately, climate change impacts on flooding are difficult to recognize partly due to geographically sparse flood records from catchments with natural flow regime and short instrumental datasets. Detection of temporal changes on local and regional flooding therefore requires long-term records to overcome the problems derived from their natural inter-annual and inter-decadal rainfall variability, particularly in Mediterranean climates. Natural sedimentary archives such as lake records provide centennial- to millennial-length flood reconstructions allowing to assess the dynamics of extreme events under natural climate variability beyond the instrumental period. In this scientific context FLOODARC action aimed to understand the long-term variability of extreme floods in Western Mediterranean, as well as to quantitatively assess the climate drivers. The reconstruction of past floods in different individual lacustrine records from unstudied areas of the Iberian Peninsula as well as the compilation of existing flood archives from SW Europe enabled to build a comprehensive dataset of long-term flood records in Western Mediterranean. Paleo Flood Frequency Analyses (PFFA) carried out on this paleohydrological database resulted in a useful tool to understand the spatial and temporal variability of floods at the regional level as well as to further comprehend the role of climate on flood frequency and intensity evolution. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far FLOODARC research goals were pursued following a comprehensive multidisplinar methodological approach consisting on; i) Reconstruction of past floods in different individual lacustrine records from the Iberian Peninsula. This task greatly benefited from the availability of existing material (sediment cores) and geochemical and chronological datasets from the studied sites. The flood reconstruction involved initial sediment core descriptions and thin section preparations to identify flood layers using a state-of-the-art protocol that combined detailed microfacies analyses with geochemical analyses. A second step included the compilation and further analyses of existing and ongoing paleoflood reconstructions across Western Mediterranean to characterize the different regional flood patterns. The analyzed flood records span different time intervals ranging from the last centuries in the Western Ebro Basin (NE Spain) to the last 26000 years in NW Spain. We documented a large spatial and temporal flood variability across the different geographic and climatic domains in SW Europe. We found that the ability of each individual study site to record extreme floods were strongly conditioned by local intrinsic factors. In most of the studied sites, flood variability resulted in an interplay between climate and anthropogenic drivers. Disentangling both climate and non-climatic forcings resulted crucial to quantitatively assess the climate drivers of the non-stationary behaviors of regional flood frequency and intensity.The scientific outputs of this action were spread amongst a wide research community of hydrologist and paleoclimatologists worldwide through oral and poster presentations in six international conferences. Additionally, an international PAGES workshop was co-organized by FLOODARC investigators in which the scientific findings of this action was addressed to a more specialized scientific community working in paleofloods. Scientific contributions showing the main results and scientific achievements of this action are being published in well-known SCI journals, and the applied intellectual properties are those indicated in the Guidelines on Open Access to Scientific Publications and Research Data in H2020. A Data Management Plan was developed to grant open access of the project´s deliverables to society. To communicate the knowledge generated by FLOODARC to the general public we carried out several outreach initiatives including i) scientific talks to students at Spanish local high and secondary schools as well as in French universities and; ii) seminars given at the Spanish National Science Museum during the European´s research night, targeting a non-specialist audience. Meetings with local and regional stakeholders were also regularly held to highlight the need for paleohydrological studies in flood hazard management and risk assessments. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) FLOODARC has applied, for the first time in paleohydrological studies, a rigorous multi-site approach to establish a homogeneous database of flood series covering both long time (centennial to millennial-long) and spatial (sub-continental) scales. FLOODARC made a significant contribution in the field of Paleoflood Hydrology since this action meets the needs for i) better knowledge of flood variability using natural archives, and ii) the ability to understand the role of climate on flood pattern evolution at a sub-continental scale with direct application in flood hazard estimation and management. FLOODARC has also addressed the need of expanding flood databases, both in space and time, to allow the understanding of regional flood patterns and their relationships to natural climate variability. In addition, this action contributed to the development of preliminary PFFA tools for the analyses of flood frequency, occurrence of extremes and the inter-comparison of different flood datasets. The refinement of the PFFA is expected to constitute a benchmark systematic methodology that could be implemented by the scientific community working in Flood Hydrology. These contributions may support EU policy makers to improve flood-risk management by integrating PFFA in European flood hazard assessments and risk management policies, which are major concerns in relation to natural hazards and climatic change adaptation strategies.