Age, event layer thickness and titanium µXRF counts of sediment core Mo05 obtained from Lake Mondsee, Austria

We present a record of extreme spring-summer runoff events for the past 1600 yr preserved in the varved sediments of Lake Mondsee (Austrian Pre-Alps). Combined sediment microfacies analyses and high-resolution micro-X-ray fluorescence element scanning allow us to identify 157 detrital event layers deposited in spring-summer and to discriminate between regional flood and local debris flow deposits. Higher spring-summer flood activity with a mean event recurrence of 3-5 yr occurred in several well-confined multidecadal episodes during the Dark Ages Cold Period and Medieval time (A.D. 450-480, 590-640, 700-750, and 1140-1170) as well as during the early Little Ice Age (LIA; A.D. 1300-1330 and 1480-1520). In contrast, lowest spring-summer flood activity with an event recurrence of only 30-100 yr is observed during the Medieval Climate Anomaly (A.D. 1180-1300) and the coldest interval of the LIA (A.D. 1600-1700). These findings indicate a complex relationship between temperature conditions and extreme hydro-meteorological events and suggest that enhanced summer Mediterranean cyclogenesis triggers large-scale floods in the northeast Alps during climatic transitions. The Lake Mondsee data demonstrate the climatic sensitivity of spring-summer floods and prove the potential of varved sediment records to investigate the impact of changing climate boundary conditions on seasonal flood activity for pre-instrumental time.