Flash floods in the Tatra Mountain streams: Frequency and triggers J.A. Ballesteros-Cánovas a,b, ⁎, B. Czajka c , K. Janecka c , M. Lempa c , R.J. Kaczka c , M. Stoffel a,b a Dendrolab.ch, Institute of Geological Sciences, University of Berne, 3012 Berne, Switzerland b Climatic Change and Climate Impacts, Institute for Environmental Sciences, University of Geneva, 1227 Carouge, Switzerland c Faculty of Earth Sciences, University of Silesia, Poland HIGHLIGHTS • Flash floods represent a common natural hazard in the Tatra Mountains. • Tree ring analysis is the most suitable approach in mountain forested areas. • We report a flash flood chronology from 4 ungauged catchments covering the last 148 years. • We identify the common meteorological conditions acting as triggers of flash flood events. abstract article info Article history: Received 2 November 2014 Received in revised form 22 December 2014 Accepted 22 December 2014 Available online xxxx Editor: D. Barcelo Keywords: Paleohydrology Dendrogeomorphology Hydrometeorological triggers Tatra Mountains Poland Norway spruce Flash floods represent a frequently recurring natural phenomenon in the Tatra Mountains. On the northern slopes of the mountain chain, located in Poland, ongoing and expected future changes in climate are thought to further increase the adverse impacts of flash floods. Despite the repeat occurrence of major floods in the dense- ly populated foothills of the Polish Tatras, the headwaters have been characterized by a surprising lack of data, such that any analysis of process variability or hydrometeorological triggers has been largely hampered so far. In this study, dendrogeomorphic techniques have been employed in four poorly-gauged torrential streams of the northern slope of the Tatra Mountains to reconstruct temporal and spatial patterns of past events. Using more than 1100 increment cores of trees injured by past flash floods, we reconstruct 47 events covering the last 148 years and discuss synoptic situations leading to the triggering of flash floods with the existing meteoro- logical and flow gauge data. Tree-ring analyses have allowed highlighting the seasonality of events, providing new insights about potential hydrometeorological triggers as well as a differentiating flash flood activity between catchments. Results of this study could be useful to design future strategies to deal with flash flood risks at the foothills of the Polish Tatras and in the Vistula River catchment. © 2014 Published by Elsevier B.V. 1. Introduction Flash floods in mountain catchments are typically localized but high- ly variable hydrological processes characterized by a large water- sediment discharge in a short time period causing large economic losses and fatalities (Borga et al., 2008, 2014). Their spatio-temporal analysis requires, hence, an accurate definition of rainfall and discharge variables (Tarolli et al., 2012; Viglione et al., 2010). However, the scarcity of in- strumental data and basic environmental information in these environ- ments typically leads to considerable uncertainties (Brázdil et al., 2006), hampering our understanding of climate–process linkages and conse- quently the assessment of existing hazards (de Jong et al., 2009; Merz et al., 2014). The most accurate alternative to overcome this lack of data in forest- ed mountain catchment is the paleohydrology analysis based on tree- ring data (i.e., dendrogeomorphic methods, Stoffel et al., 2010; Ballesteros-Cánovas et al., in review). Highly-resolved tree-ring records from trees affected by flash floods allow tracking of past process activity with high spatial and temporal accuracy (Stoffel et al., 2006; Schneuwly-Bollschweiler et al., 2012). Over the last decades, the applica- tion of dendrogeomorphic analysis in paleohydrology studies has primar- ily focused on the analysis of flash flood histories at the level of specific catchment (e.g., Astrade and Bégin, 1997; St. George and Nielsen, 2003; Zielonka et al., 2008; Ruiz-Villanueva et al., 2010; Ballesteros-Cánovas et al., in press; Šilhan, 2014), and, in combination with hydraulic models, for the estimation of peak discharge (Yanosky and Jarrett, 2002; Ballesteros-Cánovas et al., 2011a,b). Dendrogeomorphic investigations are also of value at larger scales (Procter et al., 2011; Šilhán, in review), even more so as it is generally recognized that catchments located within homogenous regions may lead to varied hydrological responses. Such Science of the Total Environment 511 (2015) 639–648 ⁎ Corresponding author at: Dendrolab.ch, Institute of Geological Sciences, University of Berne, 3012 Berne, Switzerland. E-mail address: juan.ballesteros@dendrolab.ch (J.A. Ballesteros-Cánovas). http://dx.doi.org/10.1016/j.scitotenv.2014.12.081 0048-9697/© 2014 Published by Elsevier B.V. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv