Floods; Headwaters; Dendrogeomorphology; Seasonal dating; Climate trigger; Climate oscillation

Unlike large rivers, floods in headwaters have been poorly documented despite the fact that greater discharges are expected in such areas due to ongoing rainfall intensification. The purpose of this study is to carry out intra-annual dating of past floods combined with analysis of their climate linkages which may point on distribution and origin of floods. To this end, we applied dendrogeomorphic dating of impact scars on riparian vegetation to provide flood chronologies in twelve headwaters of eastern Czechia and determined their seasonal occurrences. Furthermore, we analyzed the precipitation indices and evaluated the flood events using reanalysis of pressure fields and the climate oscillation indices, particularly those representing the North Atlantic, Scandinavian, and East Atlantic/Western Russian patterns. Based on 434 dated trees, we identified 22–31 flood event years in each region over the last 70 years. The most frequent floods occurred from May to July. In addition, in ten event years it was possible to identify multiple flood events: for example May and July–August floods in 2010, 2014, and 2016. The monthly precipitation showed the strongest, but still weak, correlation with indices of Scandinavian climate oscillation during summer months (Rs = 0.23–0.42; p < 0.00), suggesting the influence of a blocking anticyclone over Scandinavia and wet air propagation to central Europe. This finding was also confirmed by the most frequent positions of low-pressure centers located east of the study sites except for the region with western orographic enhancement. In addition, timing shift of extreme precipitation to earlier period was identified at two out of three regions. We conclude that intra-annual dating of floods supported by analyses of climate extremes provides new data from sparsely gauged headwaters, thereby supplementing the information on possible changes in flood occurrences during ongoing climate change.