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| Titel |
Flood triggering in Switzerland: the role of daily to monthly preceding precipitation |
| VerfasserIn |
P. Froidevaux, J. Schwanbeck, R. Weingartner, C. Chevalier, O. Martius |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 19, no. 9 ; Nr. 19, no. 9 (2015-09-17), S.3903-3924 |
| Datensatznummer |
250120810
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| Publikation (Nr.) |
 copernicus.org/hess-19-3903-2015.pdf |
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| Zusammenfassung |
Determining the role of different precipitation periods for peak discharge
generation is crucial for both projecting future changes in flood probability
and for short- and medium-range flood forecasting. In this study,
catchment-averaged daily precipitation time series are analyzed prior to
annual peak discharge events (floods) in Switzerland. The high number of
floods considered – more than 4000 events from 101 catchments have been
analyzed – allows to derive significant information about the role of
antecedent precipitation for peak discharge generation. Based on the analysis
of precipitation times series, a new separation of flood-related
precipitation periods is proposed: (i) the period 0 to 1 day before flood
days, when the maximum flood-triggering precipitation rates are generally
observed, (ii) the period 2 to 3 days before flood days, when longer-lasting
synoptic situations generate "significantly higher than
normal" precipitation amounts, and (iii) the period from 4 days
to 1 month before flood days when previous wet episodes may have
already preconditioned the catchment. The novelty of this study lies in the
separation of antecedent precipitation into the precursor antecedent
precipitation (4 days before floods or earlier, called PRE-AP) and the short
range precipitation (0 to 3 days before floods, a period when precipitation
is often driven by one persistent weather situation like e.g., a stationary
low-pressure system). A precise separation of "antecedent" and
"peak-triggering" precipitation is not attempted. Instead, the strict
definition of antecedent precipitation periods permits a direct comparison of
all catchments.
The precipitation accumulating 0 to 3 days before an event is the most
relevant for floods in Switzerland. PRE-AP precipitation has only a weak and
region-specific influence on flood probability. Floods were significantly
more frequent after wet PRE-AP periods only in the Jura Mountains, in the
western and eastern Swiss plateau, and at the outlet of large lakes. As a
general rule, wet PRE-AP periods enhance the flood probability in catchments
with gentle topography, high infiltration rates, and large storage capacity
(karstic cavities, deep soils, large reservoirs). In contrast, floods were
significantly less frequent after wet PRE-AP periods in glacial catchments
because of reduced melt.
For the majority of catchments however, no significant correlation between
precipitation amounts and flood occurrences is found when the last 3 days
before floods are omitted in the precipitation amounts. Moreover, the PRE-AP
was not higher for extreme floods than for annual floods with a high
frequency and was very close to climatology for all floods. The fact that
floods are not significantly more frequent nor more intense after wet PRE-AP
is a clear indicator of a short discharge memory of Pre-Alpine, Alpine and
South Alpine Swiss catchments. Our study poses the question whether the impact
of long-term precursory precipitation for floods in such catchments is not
overestimated in the general perception. The results suggest that the
consideration of a 3–4 days precipitation period should be sufficient to
represent (understand, reconstruct, model, project) Swiss Alpine floods. |
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