Analisi modellistica di un evento estremo: 34 Novembre 1966

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Analisi modellistica di un evento estremo 3-4
Novembre 1966
Risultati preliminari dal progetto congiunto
Flood 66 tra ECMWF (R. Buizza, S. Uppala, E.
Klinker), ISAC-CNR (A. Buzzi, P.Malguzzi),
Università di Brescia, Dip. Ing. Civile (G.
Grossi, R. Ranzi, B. Bacchi)
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FLOOD 66
Grosseto
Venezia
Firenze
Dolomiti bellunesi

• Major widespread hystorical storm and flood
  event, which caused disasters mainly in Tuscany
  (Florence, Grosseto and other towns) and in other
  parts of central and north-eastern Italy, such as
  Venice (highest tide on record), Trento and in
  many valleys situated in Veneto and Friuli, in
  Eastern Alps, Emilia etc. in the period 3-5
  November.

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Objectives

• Use the ERA database to analayze the extreme
  event and to assess the value of the ERA-40 for
  a-posteriori studies of the ECMWF forecasting
  system value for weather risk assessment.
• Examine the accuracy of deterministic and
  probabilistic forecasts during the period of the
  1966 flood in Florence and in the Eastern Alps
• Investigate the possibility of using forecasts to
  drive river-basin discharge hydrological models
  using direct model output from a meteorological
  model chain, including hydrostatic and
  non-hydrostatic, cloud-resolving models.

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Tuscany (Arno and Ombrone River basins)

• extreme event for precipitation intensity,
  extension and continuity most of the rain fell
  on 4 November

200
200
200
400
300
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The Eastern Alps (Adige and other river basins)
250
Most of precip. fell 3-4 November)
500
400
700
250
500
400
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Z500 TL511L60 analysis 12 UTC of 1-4 November

• This figure shows the TL511L60 analyses at 12UTC
  of 1-4 November.
• Contour interval is 4dam.

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ERA40 and TL511L60 analyses 12 UTC of 1-2
November

• The ERA-40 (TL159L60, left) and the TL511L60
  (right) analyses at 12UTC of 1 and 2 November are
  very similar (ci is 2dam for full fields and 1dam
  for difference).

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MSLP, 4 Nov. 1966, 00 and 12 UTC. ECMWF ERA-40
special high-resolution (TL511L60), interpolated
on the BOLAM grid
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950 hPa wind, 4 Nov. 1966, 00 and 12 UTC. ECMWF
ERA-40 special high-resolution (TL511L60),
interpolated on the BOLAM grid
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500 hPa wind, 4 Nov. 1966, 00 and 12 UTC. ECMWF
ERA-40 special high-resolution (TL511L60),
interpolated on the BOLAM grid
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24h TP ECMWF TL511L60 deterministic forecasts
for 3-4 Nov (168h, 120h, 72h)
t96-120h
t144-168h

• This figure shows TL511L60 forecasts of
  24h-accumulated precipitation started at 12UTC of
  the 27 (144-168h) and 29 (96-120h) October, and 1
  November (48-72h) and valid for 3-4 November.
• The right-bottom panel shows a proxi for
  verification defined by the TL511L60 24h forecast
  started at 12UTC of 3 November.
• Contour isolines are 2-25-50-75-100-150-300 mm
  for precipitation.

t48-72h
3-4 Nov
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24h TP EPS fc from 30 Oct for 3-4 Nov (96-120h)
P(TPgt25mm)
P(TPgt50mm)

• This figure shows three EPS (51TL255L40)
  probabilistic forecasts started on 30 October
  (96-120h) and valid for 3-4 November, for 24-h
  accumulated precipitation in excess of 25, 50 and
  75 mm.
• The right-bottom panel shows a proxi for
  verification given by the TL511L40 24h forecast
  started on 3 November.
• Contour isolines are 2-10-20-40-60-100 for
  probabilities and 2-25-50-75-100-150-300 mm for
  precipitation.

P(TPgt75mm)
3-4 Nov
Good EPS t96-120h fc over Friuli for all
thresholds, and some signals that 75mm could hit
also Tuscany
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24h TP EPS fc from 31 Oct for 3-4 Nov (72-96h)
P(TPgt25mm)
P(TPgt50mm)

• This figure shows three EPS (51TL255L40)
  probabilistic forecasts started on 31 October
  (72-96h) and valid for 3-4 November, for 24-h
  accumulated precipitation in excess of 25, 50 and
  75 mm.
• The right-bottom panel shows a proxi for
  verification given by the TL511L40 24h forecast
  started on 3 November.
• Contour isolines are 2-10-20-40-60-100 for
  probabilities and 2-25-50-75-100-150-300 mm for
  precipitation.

3-4 Nov
P(TPgt75mm)
EPS t72-96h fc does not propagate quickly
enough, but there is a stronger signal that 75mm
could hit also Tuscany Compared to previous fc,
consistent but delayed signal, with more
localized probability values ..
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24h TP EPS fc from 1 Nov for 3-4 Nov (48-72h)
P(TPgt25mm)
P(TPgt50mm)

• This figure shows three EPS (51TL255L40)
  probabilistic forecasts started on 30 October
  (96-120h) and valid for 3-4 November, for 24-h
  accumulated precipitation in excess of 25, 50 and
  75 mm.
• The right-bottom panel shows a proxi for
  verification given by the TL511L40 24h forecast
  started on 3 November.
• Contour isolines are 2-10-20-40-60-100 for
  probabilities and 2-25-50-75-100-150-300 mm for
  precipitation.

P(TPgt75mm)
3-4 Nov
Good EPS t48-72h fc for all thresholds Compared
to previous fc, consistent but with higher and
correctly localized probability values ..
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Rianalisi ECMWF (T511, 45 km)
BOLAM 18
4 nov
3 nov
5 nov
2 nov
12 UTC 1 Nov 66
06 UTC 5 Nov
BOLAM 6 km
00 UTC 2 Nov
MOLOCH 2 km
00 UTC 3 Nov
Accumulated precipitation period
06 UTC 3 Nov
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The BOLAM 6km precipitation forecast
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The MOLOCH 2 km precipitation forecast
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The MOLOCH 2 km precipitation forecast
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The MOLOCH 2 km precipitation forecast but
starting with the NCEP reanalysis (300 km!)
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ECMWF
NCEP
Short digression about ECMWF vs NCEP reanalyses
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ECMWF
NCEP
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ECMWF
NCEP
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ECMWF
NCEP
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Some sensitivity experiments role of orography
and sea surface fluxes
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Some sensitivity experiments role of orography
and sea surface fluxes
Reference case a 24 hour FC
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Accumulated precipitation with different sea
surface fluxes
Case with different surface fluxes
No sens. lat. heat fluxes
Reference
SST 3 K
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Simulazioni idrologiche
Isarco a Chiusa A3059 km²
Adige a Bronzolo A6926 km²
Avisio a Lavis A934 km²
Adige a Trento A9763 km²
Noce a S.Giustina A1050 km²
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Esempio di risultato della modellistica
idrologica (Univ. di Brescia)
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(No Transcript)
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Conclusioni

• Levento viene ricostruito in maniera
  realistica, nonostante le incertezze nelle
  analisi e le notevoli differenze tra lanalisi
  NCEP e quella ECMWF, probabilmente associate alle
  incertezze sullAtlantico.
• Sorprende la possibilità di ricostruire campi di
  precipitazione dettagliati a partire dalle
  analisi NCEP, persino meglio che con le analisi
  ECMWF.
• Lorigine appare nelle scale grandi (crescita di
  unonda baroclina, associata a jet meridionale e
  intensa frontogenesi)
• Nonostante questo, la predicibilità appare bassa
  prima di 3 giorni la natura estrema
  dellevento non appare ad un orizzonte gt 2-3 gg.
  
• Precipitazione orografica sulle Alpi,
  apparentemente convettiva sullItalia centrale,
  questultima predicibile solo con il modello non
  idrostatico.
• Lorografia determina totalmente la distribuzione
  della precipitazione orografica e la
  ciclogenesi i flussi superficiali sono
  relativamente poco importanti.