Abstract. This paper presents three indices for evaluation of hydrometeorological extremes, considering them as areal precipitation events and trans-basin floods. In contrast to common precipitation indices, the weather extremity index (WEI) reflects not only the highest precipitation amounts at individual gauges but also the rarity of the amounts, the size of the affected area, and the duration of the event. Furthermore, the aspect of precipitation seasonality was considered when defining the weather abnormality index (WAI), which enables the detection of precipitation extremes throughout the year. The precipitation indices are complemented with the flood extremity index (FEI) employing peak discharge data. A unified design of the three indices, based on return periods of station data, enables one to compare easily interannual and seasonal distributions of precipitation extremes and large floods.The indices were employed in evaluation of 50 hydrometeorological extremes of each type (extreme precipitation events, seasonally abnormal precipitation events, and large floods) during the period 1961-2010 in the Czech Republic. A preliminary study of discrepancies among historic values of the indices indicated that variations in the frequency and/or magnitude of floods can generally be due not only to variations in the magnitude of precipitation events but also to variations in their seasonal distribution and other factors, primarily the antecedent saturation.

Abstract. This paper addresses the identification and evaluation of extreme flood events in the transitional area between western and central Europe in the period 1951-2013. Floods are evaluated in terms of three variants on an extremity index that combines discharge values with the spatial extent of flooding. The indices differ in the threshold of the considered maximum discharges; the flood extent is expressed by a length of affected river network. This study demonstrates that using the index with a higher flood discharge limit changes the floods' rankings significantly. It also highlights the high severity events.In general, we detected an increase in the proportion of warm half-year floods when using a higher discharge limit. Nevertheless, cold half-year floods still predominate in the lists because they generally affect large areas. This study demonstrates the increasing representation of warm half-year floods from the northwest to the southeast.

Precipitation extremes always have an area‐related effect, emphasizing the need for a spatial assessment of extreme precipitation events that sometimes show similar behaviour in precipitation patterns due to recurring synoptic features. Our study investigates spatial patterns in the extreme precipitation events (EPEs) that occurred in central Europe between 1961 and 2013. As many as 53 maximum events were selected by the weather extremity index (WEI), reflecting simultaneously the spatial extent and the return periods of t day precipitation totals within an event‐adjusted study area. The extremity of the EPEs is further evaluated at two lower spatial levels, the main river basins (the Rhine, Weser/Ems, Elbe, Danube, and Oder) and 20 smaller subcatchments, which enables a more detailed study of the events’ spatial structure and similarity. A correlation analysis demonstrated that heavy precipitation occurs simultaneously not only in neighbouring subcatchments but also in rather distant regions with similar orientations of mountain ranges (e.g., in the Elbe‐a and Danube‐b subcatchments). In contrast, strong negative correlations appeared between several subcatchments in the Oder and Rhine River basins, which exclude heavy precipitation from occurring simultaneously in both basins. Similar spatial patterns are obvious among precipitation extremes; using the relative WEI values as the similarity measure, agglomerative hierarchical clustering detected two well‐separated groups of events, namely, W‐CE and E‐CE, affecting mainly the western and eastern parts of central Europe, respectively. A finer division of the EPEs distinguished five clusters of events with different spatio‐temporal characteristics. Only two clusters, ED (Elbe‐Danube) and O (Oder), were represented among the top 10 central European EPEs, which occurred exclusively from the end of May to the beginning of September. Three other clusters consisted of generally lower extreme events rather equally distributed throughout the year.

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Forecasting heavy precipitation has an important role in mitigating floods and associated hazards, but it remains one of the main challenges in operational meteorology. Our previous study confirmed the close connection between large‐scale extreme precipitation events and anomalous moisture fluxes in central Europe. In this study, we introduce a variable accounting for the accumulated ascending moisture flux, which could potentially support extreme precipitation event forecasts. The variable reflects the total amount of transported water vapour in combination with extra high upward vertical velocity, which are important factors required for extreme precipitation occurrence. Looking at ERA‐Interim forecasts, we aim to determine a practical predictability and forecast skill of accumulated ascending moisture flux and compare it with the forecast skill of precipitation. While the predictability of moisture flux itself is satisfactory, generally less accurate forecasts of the vertical velocity negatively affect the predictability of accumulated ascending moisture flux, especially in the case of summer precipitation events with prevailing northern moisture flux. Nevertheless, the forecast of the proposed variable was adequate and stable up to 6 days in advance in all cases of maximum events that produced major central European summer floods. There were no such stable forecasts for less extreme events or false‐alarm precipitation extremes. Thus, we hypothesize that the calculation of the accumulated ascending moisture flux from numerical weather prediction could be useful as a supporting tool in extreme precipitation warnings in central Europe.