Abstract. The summer flood of 2013 set a new record for large-scale floods in Germany for at least the last 60 years. In this paper we analyse the key hydro-meteorological factors using extreme value statistics as well as aggregated severity indices. For the long-term classification of the recent flood we draw comparisons to a set of past large-scale flood events in Germany, notably the high-impact summer floods from August 2002 and July 1954. Our analysis shows that the combination of extreme initial wetness at the national scale -caused by a pronounced precipitation anomaly in the month of May 2013 -and strong, but not extraordinary event precipitation were the key drivers for this exceptional flood event. This provides additional insights into the importance of catchment wetness for high return period floods on a large scale. The database compiled and the methodological developments provide a consistent framework for the rapid evaluation of future floods.

ABSTRACT. Widespread flooding in June 2013 caused damage costs of €6 to 8 billion in Germany, and awoke many memories of the floods in August 2002, which resulted in total damage of €11.6 billion and hence was the most expensive natural hazard event in Germany up to now. The event of 2002 does, however, also mark a reorientation toward an integrated flood risk management system in Germany. Therefore, the flood of 2013 offered the opportunity to review how the measures that politics, administration, and civil society have implemented since 2002 helped to cope with the flood and what still needs to be done to achieve effective and more integrated flood risk management. The review highlights considerable improvements on many levels, in particular (1) an increased consideration of flood hazards in spatial planning and urban development, (2) comprehensive property-level mitigation and preparedness measures, (3) more effective flood warnings and improved coordination of disaster response, and (4) a more targeted maintenance of flood defense systems. In 2013, this led to more effective flood management and to a reduction of damage. Nevertheless, important aspects remain unclear and need to be clarified. This particularly holds for balanced and coordinated strategies for reducing and overcoming the impacts of flooding in large catchments, cross-border and interdisciplinary cooperation, the role of the general public in the different phases of flood risk management, as well as a transparent risk transfer system. Recurring flood events reveal that flood risk management is a continuous task. Hence, risk drivers, such as climate change, land-use changes, economic developments, or demographic change and the resultant risks must be investigated at regular intervals, and risk reduction strategies and processes must be reassessed as well as adapted and implemented in a dialogue with all stakeholders.

Abstract. During a 15-day episode from 26 May to 9 June 2016, Germany was affected by an exceptionally large number of severe thunderstorms. Heavy rainfall, related flash floods and creek flooding, hail, and tornadoes caused substantial losses running into billions of euros (EUR). This paper analyzes the key features of the severe thunderstorm episode using extreme value statistics, an aggregated precipitation severity index, and two different objective weathertype classification schemes. It is shown that the thunderstorm episode was caused by the interaction of high moisture content, low thermal stability, weak wind speed, and large-scale lifting by surface lows, persisting over almost 2 weeks due to atmospheric blocking.For the long-term assessment of the recent thunderstorm episode, we draw comparisons to a 55-year period regarding clusters of convective days with variable length (2-15 days) based on precipitation severity, convection-favoring weather patterns, and compound events with low stability and weak flow. It is found that clusters with more than 8 consecutive convective days are very rare. For example, a 10-day cluster with convective weather patterns prevailing during the recent thunderstorm episode has a probability of less than 1 %. IntroductionBetween the end of May and mid-June 2016, Germany and large parts of central and southern Europe were affected by an exceptionally large number of severe convective storms and related extremes such as heavy rainfall, hail, and tornadoes (Fig. 1). Rain totals exceeding 100 mm within a few hours at several locations in Germany triggered various flash floods and floods mainly in small catchments. In the town of Braunsbach in the federal state of Baden-Württemberg, for example, a severe flash flood on 29 May with a height of up to 3.5 m caused serious damage to more than 80 buildings, of which five were completely lost (Daniell et al., 2016). Only 3 days later on 1 June, extreme rain in the district of Rottal-Inn in the south of Bavaria evoked a sudden and dramatic rise in the levels of several creeks such as the Simbach, where the height increased from 20 cm to more than 5 m within only 12 h. Subsequently, the village Simbach am Inn experienced the largest flooding in history. Some of the thunderstorms during the 2 weeks also produced hail with diameters between 0.5 and 5 cm. A total of 12 tornadoes in 8 days with intensities between F0 and F1 on the Fujita intensity scale, were recorded and confirmed by the European Severe Weather Database (ESWD; Dotzek et al., 2009).The severe thunderstorms caused substantial damage to buildings, infrastructures, transportation networks, and crops. A large number of roads and railroads were blocked or severely damaged, and some villages experienced power outPublished by Copernicus Publications on behalf of the European Geosciences Union.

aBStract. -the June 2013 flood was the most severe large-scale flood in Germany, at least for the last 6 decades for which a hydrological flood severity has been calculated. Many gauges along the elbe and Danube rivers showed record water levels. the flood severity index, a measure which combines magnitude and spatial extension, is almost twice as large as the index of the august 2002 flood which has been the most expensive natural disaster for Germany to date. the enormous hydrological severity was caused by widespread and intense rainfall in combination with wet catchments due to exceptionally high rainfall in the month preceding the event. Preliminary damage estimates are in the order of 8.7 to 12 billion €. Hence, the losses seem to be lower compared to the 2002 flood (11.8 billion € for Germany). although detailed analyses have not been performed to date, it can be assumed that the investments and improvements in flood risk management since 2002 have reduced the flood risk and prevented higher damage.

At Pentecost 2014, following a period of hot weather, northwestern Germany was affected by a series of severe convective storms leading to fatalities and significant damage from strong winds, heavy precipitation, hail, and lightning. We present convection‐permitting numerical simulations for 2 days of this event (8 and 9 June) using the COnsortium for Small‐scale MOdeling (COSMO) model. Whereas a control run in a nearly operational configuration successfully reproduced the convective events of the first day, it failed to adequately reproduce the events of the second day. To further assess the predictability of this event, sensitivity studies with an enlarged model domain, finer horizontal and vertical grid spacing, and a double‐moment microphysics scheme were performed. Results show that enlarging the model domain improved the results over France and the Netherlands by better resolving deep convection and secondary cell initiation in that area, but the model failed to simulate deep convection over Germany. The increase of model resolution from 2.8 km to 2.2 and 1 km had minor effects only. However, the errors of accumulated precipitation were diminished independently of the model domain and grid resolution on the first day when using the double‐moment microphysics scheme. A better result for 9 June was obtained by using later initialization times (0300 and 0600 UTC instead of 0000 UTC). The control run initialized at 0000 UTC produced one cell, which decayed while travelling over the Netherlands. In contrast, the runs initialized later produced thunderstorms over Germany as well, due to outflow triggering or cell splitting. Finally, different cloud condensation nuclei (CCN) assumptions revealed a systematic relationship for condensate amounts of cloud water, rain and ice with increasing CCN. However, the evaporation of raindrops at lower levels led to a non‐systematic response of accumulated precipitation to CCN. In addition, grid spacing effects on aerosol–cloud interactions were assessed.