Abstract
River discharge is impacted by the sub-seasonal (weekly to monthly) temporal structure of precipitation. One example is the successive occurrence of extreme precipitation events over sub-seasonal timescales, referred to as temporal clustering. Its potential effects on discharge have received little attention. Here, we address this question by analysing discharge observations following extreme precipitation events either clustered in time or occurring in isolation. We rely on two sets of precipitation and discharge data, one centered on Switzerland and the other over Europe. We identify "clustered" extreme precipitation events based on the previous occurrence of another extreme precipitation within a given time window. We find that clustered events are generally followed by a more prolonged discharge response with a larger amplitude. The probability of exceeding the 95th discharge percentile in the five days following an extreme precipitation event is in particular up to twice as high for situations where another extreme precipitation event occurred in the preceding week compared to isolated extreme precipitation events. The influence of temporal clustering decreases as the clustering window increases; beyond 6–8 weeks the difference with non-clustered events is negligible. Catchment area, streamflow regime and precipitation magnitude also modulate the response. The impact of clustering is generally smaller in snow-dominated and large catchments. Additionally, particularly persistent periods of high discharge tend to occur in conjunction with temporal clusters of precipitation extremes.
Highlights
Extreme precipitation accumulations over relatively short sub-seasonal time windows can increase water levels in rivers and lakes, and lead to floods
The influence of clustering is more strictly decreasing with increasing length of the clustering window, whereas results for Switzerland showed some discrepancies – for instance the discharge response being larger after 6-week than after 4-week clustered events (Fig. 3-a,b,c). 225 We do not investigate the influence of elevation in the European data; first, because it covers a much narrower range of elevations; second, because mean elevations are less representative of the elevation distribution in larger catchments; and third, because unlike in Switzerland, the presence of snow is dictated by other catchment characteristics
We quantified the effects of temporal clusters of extreme precipitation (TCEP) at sub-seasonal timescales on the occurrence and temporal persistence of high discharge in Switzerland and Europe
Summary
Extreme precipitation accumulations over relatively short sub-seasonal time windows can increase water levels in rivers and lakes, and lead to floods. Such accumulations can result from persistence in precipitation, either as moderate precipitation stretching over many successive days, or as several extreme precipitation episodes separated by a few days or weeks (Merz and Blöschl, 2003), referred to as temporal clusters of extreme precipitation (TCEP) (Kopp et al, 2021; Tuel and Martius, 2021a). The impact of sub-seasonal TCEP on discharge has not been explicitly addressed, to our knowledge, except briefly in the case of Switzerland by Tuel and Martius (2021b) They argued that TCEP increased the likelihood and duration of high discharge events compared to precipitation extremes occurring in isolation
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