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| Titel |
Recurring features of extreme autumnall rainfall events on the Veneto coastal area |
| VerfasserIn |
A. Barbi, M. Monai, R. Racca, A. M. Rossa |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1561-8633
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| Digitales Dokument |
URL |
| Erschienen |
In: Natural Hazards and Earth System Science ; 12, no. 8 ; Nr. 12, no. 8 (2012-08-07), S.2463-2477 |
| Datensatznummer |
250011041
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| Publikation (Nr.) |
 copernicus.org/nhess-12-2463-2012.pdf |
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| Zusammenfassung |
Recent recurring episodes of heavy flash flood-producing rainfall events on
the Veneto coastal area have renewed the interest in documenting the
frequency and key dynamical ingredients of such events. A climatological
analysis of the precipitation in Veneto reveals that, in comparison with the
rest of the region, the coastal area is characterized by fewer rain days,
lower rainfall accumulations, yet more days with heavy precipitation. If set
in relation to the yearly rainfall, daily accumulation can reach values as
high as 40% of the yearly total rainfall, more regularly between 15%
and 30%, often in periods of 12 h or less.
Four such heavy rainfall events were analyzed and synthetically described to
highlight key ingredients which appear instrumental in producing the high
rainfall accumulations. These comprise an upper-level trough elongating or
cutting off into the Western Mediterranean basin after a period of one to
two weeks of anticyclonic fair weather conditions with temperatures above
normal. The moisture supply over the Adriatic onto north-eastern Italy is
favoured by above normal sea surface temperatures, enhanced advection by a
surface low in the Gulf of Genoa, and in three of the four cases, an
additional surface low over southern Italy. The air flows associated with
the upper-level trough for the cases discussed were of moderate to weak
intensity, and convectively conditionally unstable. The flow intensity was
such that the lower tropospheric portion was blocked by and forced to flow
around the Alpine barrier, i.e. manifesting as a north-easterly, low-level
flow over much of the north-eastern Italian plains. This blocked flow seemed
to interact with the larger-scale synoptic flow to form a distinct and
persistent low-level convergence in the area of the Veneto coast.
It is suggested that these low-level convergence patterns are key in
releasing the convective instability present in the larger-scale flow just
on the Veneto coastal area. Hereby, it is the synoptic rather than the
convective setting which dictated the observed timescales of intense
rainfall. Therefore, the convective rainfall rates paired with the synoptic
durations combine to produce the exceptionally high rainfall accumulations
observed. Cases like these are significant contributors to forming the
coastal precipitation climatology, which for this area is found to be
distinctly different than for the rest of the region in terms of
precipitation concentration. |
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