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.
RCM simulations captured the basic seasonal dependence of the T‐P relationship over Europe. The simulated T‐P relationship pattern is more strongly influenced by an RCM than a driving GCM. The simulations of the CCLM4‐8‐17 RCM demonstrated noticeably better agreement with observed T‐P relationship fields than the RCA4 RCM simulations. The T‐P relationship simulated by RCA4 tends to shift to positive values in comparison to E‐OBS. These findings were found for both TPI and T‐P correlation.
The strongest Czech windstorms from 1961 to 2010 were evaluated using a weather extremity index. The index combines the return periods of station wind gusts and the size of the affected area allowing determination of the duration of individual events. Of 50 extreme wind events (EWEs), most were synoptic‐scale windstorms that occurred between the end of October and the beginning of March. However, six EWEs were categorized as the convective‐scale windstorms. Four of the strongest Czech and European windstorms were related to one other (Kyrill, the November 1984 storm, Vivian and Wiebke, and Jeanette). Approximately 90% of the synoptic‐scale windstorms were characterized by strong westerly or northwesterly flow at the 850 hPa level and a north–south temperature gradient at the 500 hPa level. The remaining (rather weaker) synoptic‐scale events were characterized by southerly flow and a west–east temperature gradient at the 850 and 500 hPa levels, respectively.
To determine the abnormality of windstorms by season, a weather abnormality index was used to evaluate 50 abnormal wind events (AWEs). Throughout the summer, as well as in half of May and September, AWEs were categorized as the convective‐scale windstorms accompanied by weak 850 hPa winds. Apart from two events with easterly winds, the remaining AWEs were accompanied by winds from the southwest and a strong west–east temperature gradient at the 850 hPa level. Ten of the latter events occurred in the last two ten‐day periods of July and first two ten‐day periods of August. All of the events followed hot episodes, and seven of them followed one of the 25 extreme high‐temperature events. A less pronounced relationship between wind and temperature anomalies was present in the colder half of the year from October to March: three of the strongest Czech EWEs were associated with abnormal high‐temperature events (AHEs).
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