Rivers in the sky, flooding on the ground: the role of atmospheric rivers in inland flooding in central Europe

Monica Ionita,Bin Guan,Viorica Nagavciuc

doi:10.5194/hess-24-5125-2020

Abstract

Abstract. The role of large-scale atmospheric circulation and atmospheric rivers (ARs) in producing extreme flooding and heavy rainfall events in the lower part of the Rhine catchment area is examined in this study. Analysis of the largest 10 floods in the lower Rhine, between 1817 and 2015, shows that all these extreme flood peaks have been preceded up to 7 d in advance by intense moisture transport from the tropical North Atlantic basin in the form of narrow bands also known as atmospheric rivers. Most of the ARs associated with these flood events are embedded in the trailing fronts of the extratropical cyclones. The typical large-scale atmospheric circulation leading to heavy rainfall and flooding in the lower Rhine is characterized by a low pressure center south of Greenland, which migrates toward Europe, and a stable high pressure center over the northern part of Africa and the southern part of Europe and projects on the positive phase of the North Atlantic Oscillation. On the days preceding the flood peaks, lower (upper) level convergence (divergence) is observed over the analyzed region, which indicates strong vertical motions and heavy rainfall. Vertically integrated water vapor transport (IVT) exceeds 600 kg m−1 s−1 for the largest floods, marking these as very strong ARs. The results presented in this study offer new insights regarding the importance of moisture transport as a driver of extreme flooding in the lower part of the Rhine catchment area, and we show, for the first time, that ARs are a useful tool for the identification of potentially damaging floods in inland Europe.

Highlights

The intensity and frequency of precipitation extremes and floods have increased over the last few decades in many parts of the world (Blöschl et al, 2015; Stadtherr et al, 2016)
We have found that all the atmospheric rivers (ARs) that have passed the western part of Europe prior to the flood peaks associated with an anticyclonic Rossby wave breaking (ARWB; Table 2), which is in agreement with the study of Zavadoff and Kirtman (2020), who showed that ARs over the western part of Europe are linked mostly with ARWB, and is in broad consistency with Hu et al (2017), who found most of the AR landfalls along the northern coast of western USA were associated with ARWB
While ARs are essential ingredients for producing heavy rainfall events and flooding over the coastal areas of the European continent (e.g., Portugal, Spain, France and Norway) little is known about their influence on the precipitation and flood events in inland Europe (Gimeno et al, 2016)

Summary

Introduction

The intensity and frequency of precipitation extremes and floods have increased over the last few decades in many parts of the world (Blöschl et al, 2015; Stadtherr et al, 2016). Among the most costliest and damaging floods in Europe, we have the 1993 and 1995 winter floods in France, Germany, the Netherlands and Belgium (Chbab, 1995; Disse and Engel, 2001; Engel, 1997; Fink et al, 1996); the 2000, 2007 and 2014 floods in the UK (Kelman, 2001; Muchan et al, 2015; Posthumus et al, 2009; Stevens et al, 2016); the 2002 and 2013 damaging floods in the Elbe river catchment area (Ulbrich et al, 2003a, b; Ionita et al, 2015); the 2005 floods in the eastern part of Europe (Barredo, 2007; Ionita, 2015); and the 2010 floods in the central part of Europe (Bissolli et al, 2011), among others These recent floods, recorded at different parts of the European continent, have shown that coping with floods is not trivial, and for a better management and improvement of flood predictions, it is necessary to improve our understanding of the underlying mechanisms of these extreme events. Taking into account the fact that climate change is expected to lead to an intensification in the hydrological cycle and, in particular, the hydrological extremes

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Conclusion