Extreme floods in central Europe over the past 500 years: Role of cyclone pathway “Zugstrasse Vb”

Abstract

Anthropogenically induced climate change has been hypothesized to add to the risk of extreme river floods because a warmer atmosphere can carry more water. In the case of the central European rivers Elbe and Oder, another possibility that has been considered is a more frequent occurrence of a weather situation of the type “Zugstrasse Vb,” where a low‐pressure system travels from the Adriatic region northeastward, carrying moist air and bringing orographic rainfall in the mountainous catchment areas (Erzgebirge, Sudeten, and Beskids). Analysis of long, homogeneous records of past floods allows us to test such ideas. M. Mudelsee and co‐workers recently presented flood records for the middle parts of the Elbe and Oder, which go continuously back to A.D. 1021 and A.D. 1269, respectively. Here we review the reconstruction and assess the data quality of the records, which are based on combining documentary data from the interval up to 1850 and measurements thereafter, finding both the Elbe and Oder records to provide reliable information on heavy floods at least since A.D. 1500. We explain that the statistical method of kernel occurrence rate estimation can overcome deficiencies of techniques previously used to investigate trends in the occurrence of climatic extremes, because it (1) allows nonmonotonic trends, (2) imposes no parametric restrictions, and (3) provides confidence bands, which are essential for evaluating whether observed trends are real or came by chance into the data. We further give a hypothesis test that can be used to evaluate monotonic trends. On the basis of these data and methods, we find for both the Elbe and Oder rivers (1) significant downward trends in winter flood risk during the twentieth century, (2) no significant trends in summer flood risk in the twentieth century, and (3) significant variations in flood risk during past centuries, with notable differences between the Elbe and Oder. The observed trends are shown to be both robust against data uncertainties and only slightly sensitive to land use changes or river engineering, lending support for climatic influences on flood occurrence rate. In the case of winter floods, regional warming during the twentieth century has likely reduced winter flood risk via a reduced rate of strong river freezing (breaking ice at the end of winter may function as a water barrier and enhance a high water stage severely). In the case of summer floods, correlation analysis shows a significant, but weak, relation between flood occurrence and meridional airflow, compatible with a “Zugstrasse Vb” weather situation. The weakness of this relation, together with the uncertainty about whether this weather situation became more frequent, explains the absence of trends in summer flood risk for the Elbe and Oder in the twentieth century. We finally draw conclusions about flood disaster management and modeling of flood occurrence under a changed climate.

Floods in the Upper Part of Vistula and Odra River Basins in the 19th and 20th Centuries / Powodzie W Górnej Części Dorzeczy Wisły I Odry W XIX I XX Wieku

“…Geographical and environmental conditions in the upper part of the Vistula and Odra Rivers basins are conducive to floods both in the summer and winter seasons [13]. The analyses conducted for the 19 th and 20 th centuries demonstrate that two main types of floods can be distinguished.…”

Variability of high rainfalls and related synoptic situations causing heavy floods at the northern foothills of the Tatra Mountains

“…Orography is a crucial precipitation-causing factor in all high mountain areas (Sénési et al 1996;Buzzi et al 1998;Massacand et al 1998;Buzzi and Foschini 2000;Ferretti et al 2000;Schneidereit and Schär 2000;Houze 2001;Rotunno and Ferretti 2001;Pradier et al 2004;Seibert et al 2007). Typical cyclonic circulation types with air advection from the northern sector, cyclonic centre or cyclonic trough have been declared responsible for the most severe precipitation-induced flood events in the region (Morawska-Horawska 1971;Niedźwiedź 2003a, b;Mudelsee et al 2004;Czekierda 2001, 2009) as well as in the wider areas of Central Europe (James et al 2004). Figure 6 illustrates the spatial distribution of air pressure at sea level and selected geopotential heights (300, 500, 700 and 850 hPa) based on the NCEP/NCAR reanalysis data set (Kalnay et al 1996) for 9 days with precipitation ≥100 mm in Zakopane and serious flooding in the Polish Tatras.…”

Grenzen und Herausforderungen der regionalen Klimamodellierung

“…Auch an der Entwicklung extremer Niederschläge in Deutschland sind die Alpen beteiligt (Mudelsee et al 2004). Solche Starkregen führten in den vergangenen Jahren zu großen Überflutungen an Elbe, Oder und Donau (Schröter et al 2013 .…”