Karolina Janecka

Floods at the northern foothills of the Tatra Mountains — A Polish-Swiss research project

The present paper introduces the topical area of the Polish-Swiss research project FLORIST (Flood risk on the northern foothills of the Tatra Mountains), informs on its objectives, and reports on initial results. The Tatra Mountains are the area of the highest precipitation in Poland and largely contribute to flood generation. The project is focused around four competence clusters: observation-based climatology, model-based climate change projections and impact assessment, dendrogeomorphology, and impact of large wood debris on fluvial processes. The knowledge generated in the FLORIST project is likely to have impact on understanding and interpretation of flood risk on the northern foothills of the Tatra Mountains, in the past, present, and future. It can help solving important practical problems related to flood risk reduction strategies and flood preparedness.

Flash floods in the Tatra Mountain streams: Frequency and triggers

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 densely 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 meteorological 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.

Changes of flood risk on the northern foothills of the Tatra Mountains

The present paper reviews selected outcomes of the FLORIST project devoted to flood risk in the region of the northern foothills of the Tatra Mountains in Poland and summarizes novel results. The project encompassed theoretical, field, and modeling work. It was focused around observation-based hydroclimatology; projections for the future; dendrogeomorphology; as well as influence of transport of large wood on fluvial processes. The project improved understanding and interpreting changes in high-flow frequency and magnitude as well as changes in flood risk in the region, related to the presence of large wood in mountain streams. A unique database on past episodes of intense precipitation and flooding was created, harnessing multiple sources. The project showed that the analysis of tree rings and wood logs can offer useful information, complementing and considerably enriching the knowledge of river floods in the region of northern foothills of the Tatra Mountains. Retrospective and scenario-defined modeling of selected past fluvial events in the region was also performed.

Climate Reconstruction from Tree-Rings in the Tatra Mountains

This chapter examines the long-term variability of summer (June–July) air temperature and summer humidity (precipitation and Standardised Precipitation Evapotranspiration Index, SPEI) in the region of the Tatra Mountains, which represents natural climate conditions, free of strong anthropogenic influences. The reconstruction of temperature is available for the period since the beginning of the 17th century and reconstruction of humidity related parameters since the beginning of the 18th century by means of the methods based on the tree-ring chronologies. The main proxies utilized for temperature reconstruction were tree-ring widths of Norway spruce (Picea abies (L.) H. Karst) and Stone pine (Pinus cembra L.) growing in the timberline ecotone. The precipitation and SPEI were reconstructed based on Scots pine (Pinus sylvestris L.) tree-ring widths of trees growing at ~1000 m a.s.l. The reconstruction of summer temperature from tree-rings pointed to a relatively cold interval as a part of the Little Ice Age (from the mid 16th to late 19th centuries). In the 20th and at the beginning of the 21st centuries, general increase of air temperature was observed. However, in this recent warm period and during earlier main climatic periods, temperature conditions were not uniform. Analysing series of summer temperature (the 17th–21st centuries) several shorter warm and cool fluctuations were observed. The reconstructed humidity variables exhibited less variability. This is the first attempt of precipitation reconstruction in mountains regions based on the tree-ring chronologies. But the correlation between flood events and humid periods is poor due to the predominant character of the flood caused by short term intensive precipitation of short duration.

Deciphering Flood Event Information from Tree-Ring Data in the Tatra Mountains: Implications for Hazard Assessment

Mountains and their foothills are areas where intense floods are characterized by high discharge and where they occur more often than in lowlands. Furthermore, due to the fact that they are mainly caused by short-lasting heavy rainfall events, they are difficult to predict. The dense network of meteorological stations and river gauges is crucial to understand hydrological processes and to forecast floods. Most mountain regions suffer from a scarcity of instrumental data that are long enough for scientific purposes. In such cases where historical data or instrumental records are lacking, floods in forested catchments can be analysed by using growth series from trees growing along stream channels. In the streams draining the northern slopes of the Tatra Mountains, it was possible to reconstruct the occurrence and magnitude of paleofloods using tree-ring data. More than 1100 increment cores were sampled from 218 Picea abies and Abies alba trees growing at 6 stream sectors and allowed determination of 480 growth disturbances and a definition of the magnitude of 47 flood events between A.D. 1866 and 2012. In this region, floods are triggered by intense and prolonged rainfall events in spring and summer. These paleoflood records also allowed construction of a regional flood analysis and to reduce the uncertainties in the flood frequency assessment.