The frequency, intensity, and origin of floods in Poland in the 11th–15th centuries based on documentary evidence.

• A total of 166 floods were recorded in the study period. The greatest number (102, i.e. 61.4%) was noted in the 15th century. • Floods were registered most often for the Vistula River basin (84 cases). Significantly fewer floods (69) were observed in the Oder River basin. • The "above average or supra-regional floods" category was most common (77 cases) in Poland in the period 1001–1500 according to the classification of Brázdil et al. (2006). • The main reason for floods in Poland in the 11th–15th centuries was the three sub-types of rain (47.6%, 79 cases). Documentary evidence is increasingly being recognized as a precious source for assessing flood records. We have used this type of proxy data to identify the occurrence of floods in Poland from the 11th to the 15th centuries. In addition, we estimated the intensity of each flood event using the best-known classifications for Europe (Barriendos and Coeur, 2004; Brázdil et al., 2006) and assessed their origin based on modified Lambor's (1954) criteria. The database of floods in Poland contains 166 occurrences in the study period. Most occurred in the 15th century (61.4%). Of the studied regions, Silesia and the Baltic Coast and Pomerania regions were the two most affected by flood events, each accounting for 33–34% of instances. Based on the Brázdil et al. (2006) classification, 77 of the recorded floods are above-average or supra-regional. Also, the indexation of floods based on Barriendos and Coeur (2004) demonstrated that 99 were extraordinary flood events. Rain and its subtypes were the leading causes of floods, with 79 records (47.6%). Flood occurrence in Poland exhibited good spatial coherency with neighboring countries. The updated and most complete inventory of floods in medieval Poland that we present here with a detailed analysis of their frequency, intensity and origin, improves the existing knowledge about this phenomenon in Central Europe. The results of this study, similarly to many other previous studies, also confirm the great capacity for documentary evidence to provide valuable and reliable information about flood records for the pre-instrumental period. [ABSTRACT FROM AUTHOR]