Flood occurrences and characteristics in Poland (Central Europe) in the last millennium

In the current era of global climate change, extreme events such as flood exposure are increasing globally. Knowledge about floods during historical periods is limited worldwide, mainly due to gaps in the documentary evidence and the lack of a reliable, comprehensive database. A new comprehensive database of floods in Poland in the 11th-18th centuries was created using quality-controlled documentary evidence. In addition, a list of floods for the 19th and 20th centuries was created based on a literature review. Using all these data, the frequency, intensity, genesis, and spatial distribution of floods in Poland in the last millennium were investigated. Results revealed the occurrence of 1680 floods in Poland in the last millennium. The 18th century was the most abundant in recorded floods (356, 21 %). Floods in the period 1001-1800 were most frequent in the Silesia region (553, 43 %) and in the Oder River basin (671, 55 %). The number of floods was greatest in summer (JJA, 46 %) and the lowest in autumn (SON, 8 %). An investigation of the origin of floods indicated that rain was the main contributing factor to the occurrences of floods in Poland (44 %). The estimation of the intensity of floods showed that most of them were of extreme nature: "above-average, or supra-regional flood" (33 %) and "extraordinary" floods (70 %). Analysis of the multi-temporal trend demonstrated that, overall, for the periods of 1501-1700 and 1601-1800, positive trends were more numerous than negative trends, whereas, for 1801-2000, negative trends were slightly more numerous than positive trends.