Medieval Poland was hit by extreme flooding 166 times, study finds

Polish scholars studying medieval sources found that the country was hit by floods 166 times between the 11th and 15th centuries, revealing details of the causes of these disasters.

Their study, published in the Journal of Hydrology, examined floods within Poland’s modern borders, focusing on the Oder and Vistula rivers and their basins. They searched for mentions of floods in 164 different sources, including chronicles, administrative records, and even personal letters. One example can be found in the Annals of Jan Dlugosz, who recorded for the year 1475:

“The rivers are low everywhere except in Krakow, where days and nights of rain caused an unprecedented flooding of the Vistula 24 and the following three days, when the water rose to the level of the altars in the churches of St. Bernard and St. Agnes. The great bridge connecting Kazimierz and Cracow was washed away and all the gardens destroyed, but food remained cheap for the rest of the year.”

The above sounds like an account of the changes on Earth observed over the past decade.

Researchers were able to uncover several interesting aspects of flooding in medieval Poland, including that the Vistula River was more prone to these disasters compared to the Oder River. Heavy rainfall was the most commonly cited cause of flooding, while other causes included snowmelt and ice barrier formation.

When comparing periods in the Middle Ages, more than 60% of the recorded floods occurred in the 15th century, and in some years there were as many as three different floods. The researchers note that the main reason for this is that many more sources have survived in later centuries than in earlier centuries.

“However,” the researchers write, “other important reasons that floods in Poland were most often reported at this time are the observed increase in settlement and increased deforestation near rivers. From the middle of the fourteenth century, the construction of the first, but poorly constructed, dams on the Lower Vistula River paradoxically also led to an increase in the number of floods. The reason was an increase in population density in the river valley behind the dikes due to a false sense of security. In fact, they were easily and often destroyed by water”.

The study is also trying to assess the intensity of these floods and whether they were part of events that may have been seen in other regions of Eastern Europe.

Even today, floods remain a major form of natural disaster in Poland and can cause billions of dollars in damage. The researchers believe this study can also help with this modern problem. They write:

“These implications show the vulnerability of different regions of the world to flooding, emphasizing the need to improve the knowledge from which we estimate the frequency, intensity and occurrence of floods. Long-term study of floods is therefore necessary to understand them as natural phenomena and linked to anthropogenic activities.”

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