Reconstruction of floods in Poland in the last 1000 years

The reconstruction of floods in Poland in the last millennium (11th–20th centuries) was evaluated based on more than 1,300 weather notes and sources describing floods. After assessing the quality of each source, the most reliable sources were used for the investigation of flood occurrences. The most commonly used methods for the classification of flood intensity in Europe (Barriendos and Coeur 2004; Brázdil et al. 2006) have been used. The genesis of floods was estimated based on the method presented by Lambor (1954). The results demonstrated that more than 1,600 floods occurred in Poland in the last millennium. The highest number of floods occurred in the 18th (356) and 16th (345) centuries, while the lowest occurred in the 19th (187) and 11th–15th (210) centuries. Assessment of flood trend analysis based on the Mann–Kendall test showed that from 1301 to 2000 there was an increasing trend in the frequency of floods. Analysing the spatial diversity of floods in Poland in the study period indicated that the highest number of floods occurred in the Oder River basin. Also, the number of floods in the Silesia and Baltic Coast regions was significantly more than in the other four analysed regions. The estimation of the intensity of floods demonstrated that most of the floods belong to the “above-average, or supra-regional flood” and the “extraordinary” categories according to Brázdil et al. (2006) and Barriendos and Coeur (2004) classifications, respectively. The evaluation of the main genesis of floods indicated that rain and its sub-types (torrential, frontal, long-lasting, territorially widespread) were the main cause of floods in Poland in the 11th–20th centuries. Studying floods in Poland before the 21st century will improve our understanding of historical hydrology in Europe.The work was supported by the National Science Centre, Poland, project No. 2020/37/B/ST10/00710.References:Barriendos, M., Coeur, D, 2004: Flood data reconstruction in historical times from non-instrumental sources in Spain and France. Systematic, Palaeoflood and Historical Data for the Improvement of Flood Risk Estimation. Methodological Guidelines, edited by: Benito, G. and Thorndycraft, VR, Centro de Ciencias Medioambientales, Madrid, Spain, pp. 29–42.Brázdil, R., Kundzewicz, Z. W., & Benito, G., 2006: Historical hydrology for studying flood risk in Europe. Hydrological sciences journal, 51(5), 739–764. https://doi.org/10.1623/hysj.51.5.739.Lambor, J., 1954: Klasyfikacja typów powodzi i ich przewidywanie. Gospodarka Wodna, 4, 129–13