The July 2021 flood in central Europe was one of the five costliest disasters in Europe in the last half century, with an estimated total damage of EUR 32 billion. The aim of this study is to analyze and assess the flood within an interdisciplinary approach along its entire process chain: the synoptic setting of the atmospheric pressure fields, the processes causing the high rainfall totals, the extraordinary streamflows and water levels in the affected catchments, the hydro-morphological effects, and the impacts on infrastructure and society. In addition, we address the question of what measures are possible to generate added value to early response management in the immediate aftermath of a disaster. The superposition of several factors resulted in widespread extreme precipitation totals and water levels well beyond a 100-year event: slow propagation of the low pressure system Bernd, convection embedded in a mesoscale precipitation field, unusually moist air masses associated with a significant positive anomaly in sea surface temperature over the Baltic Sea, wet soils, and steep terrain in the affected catchments. Various hydro-morphodynamic processes as well as changes in valley morphology observed during the event exacerbated the impact of the flood. Relevant effects included, among many others, the occurrence of extreme landscape erosion, rapidly evolving erosion and scour processes in the channel network and urban space, recruitment of debris from the natural and urban landscape, and deposition and clogging of bottlenecks in the channel network with eventual collapse. The estimation of inundation areas as well as the derived damage assessments were carried out during or directly after the flood and show the potential of near-real-time forensic disaster analyses for crisis management, emergency personnel on-site, and the provision of relief supplies. This study is part one of a two-paper series. The second part (Ludwig et al., 2022) puts the July 2021 flood into a historical context and into the context of climate change.

Renewable energy production is strongly influenced by weather and climate. Regional climate projections can be useful to quantify climate change impacts on renewable energies. With this aim, we analyze future changes of wind speed and wind energy potentials using a multimodel ensemble of EURO‐CORDEX simulations at 12 km and three‐hourly resolution, considering nine different global and regional climate model chains. A comparison between modeled historical 10 m wind speeds and ERA‐Interim‐driven evaluation runs for the same regional climate models uncovers some substantial model biases. The bias‐corrected 10 m wind speeds are extrapolated to the hub height of a wind turbine to derive gridded wind energy output (Eout). The ensemble mean responses project only small changes of mean annual and winter Eout for large parts of Europe in future decades, but a considerable decrease for summer Eout. In terms of variability, increasing intraannual and interdaily variabilities are projected for large parts of northern, central, and eastern Europe. While the ensemble spread is quite large for interdaily variability, results are more robust for intraannual variability. With respect to wind speed characteristics relevant for wind energy production, a robust increase in the occurrence of low wind speeds (<3 m/s) is detected. Due to a combination of higher annual mean Eout and lower intraannual variability, climate change could be beneficial for regions like Baltic and Aegean Sea. For large parts of Germany, France, and Iberia, a lower mean Eout and increased intraannual variability may imply larger temporal/spatial fluctuations in future wind energy production and therefore a more challenging wind energy management.

In the last decade, the Climate Limited-area Modeling Community (CLM-Community) has contributed to the Coordinated Regional Climate Downscaling Experiment (CORDEX) with an extensive set of regional climate simulations. Using several versions of the COSMO-CLM-Community model, ERA-Interim reanalysis and eight global climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) were dynamically downscaled with horizontal grid spacings of 0.44^∘ (∼ 50 km), 0.22^∘ (∼ 25 km), and 0.11^∘ (∼ 12 km) over the CORDEX domains Europe, South Asia, East Asia, Australasia, and Africa. This major effort resulted in 80 regional climate simulations publicly available through the Earth System Grid Federation (ESGF) web portals for use in impact studies and climate scenario assessments. Here we review the production of these simulations and assess their results in terms of mean near-surface temperature and precipitation to aid the future design of the COSMO-CLM model simulations. It is found that a domain-specific parameter tuning is beneficial, while increasing horizontal model resolution (from 50 to 25 or 12 km grid spacing) alone does not always improve the performance of the simulation. Moreover, the COSMO-CLM performance depends on the driving data. This is generally more important than the dependence on horizontal resolution, model version, and configuration. Our results emphasize the importance of performing regional climate projections in a coordinated way, where guidance from both the global (GCM) and regional (RCM) climate modeling communities is needed to increase the reliability of the GCM–RCM modeling chain.