Abstract
Abstract. Regional analyses of atmospheric conditions that may cause flooding of important transport infrastructure (railway tracks, highways/roads, rivers/channels) and subsequent adaptation measures are part of topic 1 of the network of experts initiated by the German Federal Ministry of Transport and Digital Infrastructure (BMVI). As an example case study, the December 2014 flood in Schleswig-Holstein, Germany, was investigated. Atmospheric conditions at the onset of the flood event are described and evaluated with respect to the general weather circulation, initial wetness, and event precipitation. Persistent, predominantly westerly general weather circulations (GWCs) directed several low-pressure systems over the North Sea to Schleswig-Holstein during December 2014, accompanied by prolonged rainfall and finally a strong precipitation event in southern Schleswig-Holstein, causing several inland gauges to exceed their, by then maximum, water levels. Results show that the antecedent precipitation index (API) is able to reflect the soil moisture conditions and, in combination with the maximum 3-day precipitation sum (R3d), to capture the two main drivers finally leading to the flood: (1) the initial wetness of north-western Schleswig-Holstein and (2) strong event precipitation in southern and eastern Schleswig-Holstein from 21 to 23 December; at the same time, both indices exceeded their respective 5-year return periods. Further, trend analyses show that both API and R3d have been increasing during recent years, while regional patterns match the north-eastward shift of cyclone pathways, leading to a higher risk of flooding in Schleswig-Holstein. Within the network of experts, investigations of these and further indices/drivers for earth system changes (e.g. wind surge and sea level rise) derived from observations, reanalyses, and regional climate model data are planned for all German coastal areas. Results can be expected to lead to improved adaptation measures to floods under climate change conditions wherever catchments have to be drained and infrastructures and ecosystems may be harmed.
Highlights
In December 2014, predominant westerly general weather circulations (GWCs) caused a major Baltic inflow (MIB) event
Two different objective GWC classification methods were compared to describe the situation in Schleswig-Holstein (SH) during December 2014: (1) the modified Lamb weather types (LWTs; Jenkinson and Collison, 1977) used at the Federal Maritime and Hydrographic Agency (BSH; Löwe, 2005) with a model centre over the central North Sea, and (2) the objective classification (OWTC; Dittmann et al, 1995; Bissolli and Dittmann, 2001) of the German Meteorological Service (DWD) with a model centre over central Germany
The December 2014 was dominated by westerly GWCs lasting for several weeks
Summary
In December 2014, predominant westerly general weather circulations (GWCs) caused a major Baltic inflow (MIB) event (see, e.g., Lehmann et al, 2016; Post and Lehmann, 2016). Persistent rainfall in combination with an extreme precipitation event from 21 to 23 December led to the flooding of several catchment areas in SchleswigHolstein, Germany, located between the North and Baltic seas. Both events mark independent atmospheric and hydrologic responses to the GWC, illustrating the importance of interdisciplinary research in this area. In this regard, the region Schleswig-Holstein is a potent “blue spot” dealing with multiple drivers for earth system changes in the North and Baltic seas region.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
