There are concerns that recent climate change is altering the frequency and magnitudes of river floods in an unprecedented way 1 . Historical studies have identified flood-rich periods in the past half millennium in various regions of Europe 2 . However, because of the low temporal resolution of existing data sets and the relatively low number of series across Europe, it has remained unclear whether Europe is currently in a flood-rich period from a long term perspective. We analyze how recent decades compare with the flood history of Europe, using a new database composed of more than 100 high-resolution (sub-annual) historical flood series based on documentary evidence covering all major regions of Europe. Here we show that the past three decades were among the most flood-rich periods in Europe in the last 500 years, and that this period differs from other floodrich periods in terms of its extent, air temperatures and flood seasonality. We identified nine floodrich periods and associated regions. Among the periods richest in floods are 1560-1580 (Western and Central Europe), 1760-1800 (most of Europe), 1840-1870 (Western and Southern Europe), and 1990. In most parts of Europe previous flood-rich periods occurred during cooler than usual phases, however the current flood-rich period has been much warmer. In the past, the dominant flood seasons in flood-rich periods were similar to those during the intervening (interflood) periods, but flood seasonality is more pronounced in the recent period. For example, during previous flood and interflood periods, 41% and 42% of Central European floods occurred in summer respectively, compared to 55% of floods in the recent period. The uniqueness of the present-day flood-rich period calls for process-based flood risk assessment tools and flood risk management strategies that can incorporate these changes.

The flood history of the German Alpine foreland has not previously been examined in detail, even though reliable historical data up to the 13th century are available. The rivers Isar and Lech were chosen for the current investigation because their neighbouring catchments are typical of the Alpine foreland. More than 85 historical floods were recorded for each river by means of written documents. Continuous water-level records from 1826 up to the present were made available by the Bavarian Environmental Authority. The water-level records were combined with the documentary flood record by means of statistics. The 31-year running frequencies of the historical floods on the Lech and Isar show similarities, but also unexpected differences. These differences can be explained by the regional distribution of rainfall and by different morphological features of the catchments. Most of the floods on the Lech and Isar occurred during the summer season due to heavy rainfall lasting a couple of days. Long-lasting orographic rainfall in the Alpine foreland is mostly due to a low pressure system, moving northeastward from the Adriatic to the Baltic region. Therefore, the flood history of the Alpine foreland of Germany can be seen as a history of this far-reaching pressure configuration, leading to a better understanding of the summer conditions in Central Europe.

Abstract. This paper describes the flood history of the Bavarian part of the Alpine Foreland of Germany and addresses different questions concerning climate variability and flood frequencies from the 13th century until today. Will recent climatic change modify the flood frequencies within the Bavarian Alpine Foreland or are the flood frequencies varying due to altering climatic conditions since historical times? In the context of recent discussions whether man-made climate change will modify the present state of flood frequencies, a look back into the past is essential to understand the occurrence of floods in general and of recent floods in particular. In order to understand climatic variability and changes in a comprehensive way, it is necessary to review long time series. A perceived increase of summer floods in eastern Germany and Bavaria since 1997 requires examination of long time series to estimate changes in flood frequencies in a proper way. In view of the annual distribution of flood events within the Alpine Foreland of Germany, summer floods prove to be most important. Based on written historical sources, the flood history of the Alpine Foreland of Germany can be reconstructed back to the 14th century. One major result is the occurrence of "flood-rich" and "flood-poor" episodes in nearly cyclical sequences. Flood-rich periods were recorded in the periods 1300–1335, 1370–1450, 1470–1525, 1555–1590, 1615–1665, 1730–1780, 1820–1870, and 1910–1955 as well as in a 9th period beginning in 1980. The flood-rich periods are characterized by longer flood durations. Most of the flood-rich and flood-poor periods (in particular the beginning and the end of them) can be connected to changes in natural climate variability. These include changing sunspot numbers (as a measure of solar activity), so-called Little Ice Age Type Events (LIATEs) as well as changes in the North Atlantic Oscillation (NAO). Climate signals from external forcing factors, which could be used to explain the changing flood frequencies in the Bavarian Alpine Foreland, end in 1930. Relationships within the climate system such as the correlation of flood frequencies with the NAO have changed during the transition from the post Little Ice Age period to the Modern Climate Optimum around 1930. Natural climate variability might have been outperformed by anthropogenic climate change.

Abstract. This paper describes the flood sensitivity of the Bavarian part of the Alpine Foreland of Germany and addresses different questions concerning climate variability and flood frequencies, from the 14th century until today. The focal point of the paper is the flood frequency of the superordinate spatial unit of the Bavarian Foreland. Based on written historical sources, the flood history of the Alpine Foreland of Germany can be reconstructed back to the 14th century. One major result is the occurrence of "flood-rich" and "floodpoor" episodes in almost cyclical sequences. Flood-rich periods, before the 16th century based on limited available data, were recorded in the periods