Climate and floods in Central Europe since AD 1000: Data, methods, results and consequences

Knowledge of the past is a key for understanding present and future; this is especially true for climate history. This paper deals with the potential of written historical documents to reconstruct hydrological and climatological parameters and events. First of all, documentary descriptions describe the course of temperature and precipitation as well as the climatic impacts on society and the environment. Natural disasters (e.g., floods), in particular, have always attracted the attention of humankind. Besides climate itself, various geophysical and social aspects are responsible for the kind of images conveyed by the authors of historical sources. A primary aspect is the author's perception which depends on individual and social factors, which, with other aspects, can only be correctly interpreted by simultaneously using scientific and historical approaches. The results provide distinct evidence that many single flood events exceeded those of the modern period, both in terms of their impact on society and their extent (flood discharge). Furthermore, by looking at selected time series, we show that there have always been periods with relatively high or low temperature, increased flooding or less frequent flooding. Furthermore, based on documentary data, historical circulation patterns have been reconstructed. Correlating these with an integrated flood series for Central Europe, one can see that particular periods with frequent floods were associated with specific circulation patterns. Methodological problems of a thorough interpretation of flood development arise from the quantification and weighting of indices, as well as the lack of a comprehensive system describing the nature of all the processes involved. Nevertheless, it is possible to show correlations between climatic processes and other geophysical and social developments.