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)
Grosseto
FLOOD 66
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.
Objectives:
 Use the ERA database to analayze the extreme
event and to assess the value of the ERA-40 for aposteriori 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 nonhydrostatic, cloud-resolving models.
Tuscany (Arno
and Ombrone
River basins)
200
200
200
400
300
 extreme event for
precipitation
intensity,
extension and
continuity – most
of the rain fell on
4 November
The Eastern Alps (Adige
and other river basins)
250
Most of precip. fell 3-4
November)
500
400
700
250
500
400
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.
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).
MSLP, 4 Nov. 1966, 00 and 12 UTC.
ECMWF ERA-40 special highresolution (TL511L60), interpolated on
the BOLAM grid
950 hPa wind, 4 Nov. 1966, 00 and 12
UTC.
ECMWF ERA-40 special high-resolution
(TL511L60), interpolated on the BOLAM
grid
500 hPa wind, 4 Nov. 1966, 00 and 12
UTC.
ECMWF ERA-40 special high-resolution
(TL511L60), interpolated on the BOLAM
grid
24h TP: ECMWF TL511L60 deterministic
forecasts for 3-4 Nov (168h, 120h, 72h)
t+144-168h
This figure shows TL511L60
forecasts of 24h-accumulated
precipitation started at 12UTC
of the 27 (144-168h) and 29 (96120h) 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 2-25-50-75100-150-300 mm for
precipitation.
t+48-72h
t+96-120h
3-4 Nov
24h TP: EPS fc from 30 Oct for 3-4 Nov
(96-120h)
P(TP>25mm)
This figure shows three EPS
(51*TL255L40) 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 2-10-20-4060-100% for probabilities and 225-50-75-100-150-300 mm for
precipitation.
P(TP>75mm)
Good EPS t+96-120h fc over Friuli for all
thresholds, and some signals that 75mm could
hit also Tuscany …
P(TP>50mm)
3-4 Nov
24h TP: EPS fc from 31 Oct for 3-4 Nov
(72-96h)
P(TP>25mm)
This figure shows three EPS
(51*TL255L40) 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 2-10-20-4060-100% for probabilities and 225-50-75-100-150-300 mm for
precipitation.
P(TP>75mm)
P(TP>50mm)
3-4 Nov
EPS t+72-96h 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 ..
24h TP: EPS fc from 1 Nov for 3-4 Nov
(48-72h)
P(TP>25mm)
P(TP>50mm)
This figure shows three EPS
(51*TL255L40) probabilistic
forecasts started on 30 October (96120h) 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 2-10-20-40-60100% for probabilities and 2-25-5075-100-150-300 mm for
precipitation.
P(TP>75mm)
3-4 Nov
Good EPS t+48-72h fc for all thresholds …Compared to
previous fc, consistent but with higher and correctly
localized probability values ..
Rianalisi ECMWF (T511, 45 km)
2 nov
3 nov
4 nov
5 nov
12 UTC 1 Nov 66
06 UTC 5 Nov
00 UTC 2 Nov
00 UTC 3 Nov
Accumulated precipitation period
06 UTC 3 Nov
The BOLAM
6km
precipitation
forecast
The MOLOCH 2
km precipitation
forecast
The MOLOCH 2
km precipitation
forecast
The MOLOCH 2
km precipitation
forecast but
starting with the
NCEP reanalysis
(300 km!)
ECMWF
Short digression about ECMWF
vs NCEP reanalyses …
NCEP
ECMWF
NCEP
ECMWF
NCEP
ECMWF
NCEP
Some sensitivity experiments: role of orography and
sea surface fluxes…
Case with flattened orography : stronger cyclone, slightly weaker LLJ and
much weaker precipitation (a 24 hour FC)
Some sensitivity experiments: role of orography and
sea surface fluxes…
Reference case: a 24 hour FC
Accumulated precipitation with different sea surface
fluxes …
Case with different surface fluxes
Reference
No sens. lat. heat fluxes
SST + 3 K
Simulazioni
idrologiche
Isarco a Chiusa
A=3059 km²
Adige a Bronzolo
A=6926 km²
Avisio a Lavis
A=934 km²
Adige a Trento
A=9763 km²
Noce a S.Giustina
A=1050 km²
Adige River at Bronzolo [6926 km²]
prec. MOLOCH
observed runoff
simulated Bolam runoff
discharge [m³/s]
2500
0
2
4
6
8
10
12
14
2000
1500
1000
500
0
3
4
5
6
precipitation [mm]
observed precipitation
prec. BOLAM
simulated raingauge runoff
simulated Moloch runoff
7
days of November 1966
Esempio di risultato della modellistica idrologica (Univ. di Brescia)
Sieve River at Fornacina [831 km²]
prec. BOLAM
observed runoff
simulated BOLAM runoff
1600
1400
1200
1000
800
600
400
200
0
0
2
4
6
8
10
12
14
16
3
4
5
6
days of November 1966
7
precipitation [mm]
discharge [m³/s]
observed precipitation
prec. MOLOCH
Simulated raingauge runoff
simulated MOLOCH runoff
Conclusioni
 L’evento viene ‘ricostruito’ in maniera realistica, nonostante le
incertezze nelle analisi e le notevoli differenze tra l’analisi NCEP e
quella ECMWF, probabilmente associate alle incertezze sull’Atlantico.
 Sorprende la possibilità di ricostruire campi di precipitazione
dettagliati a partire dalle analisi NCEP, persino meglio che con le
analisi ECMWF.
 L’origine appare nelle scale grandi (crescita di un’onda baroclina,
associata a jet meridionale e intensa frontogenesi)
 Nonostante questo, la predicibilità appare bassa prima di 3 giorni: la
natura ‘estrema’ dell’evento non appare ad un orizzonte > 2-3 gg.
 Precipitazione orografica sulle Alpi, apparentemente convettiva
sull’Italia centrale, quest’ultima predicibile solo con il modello non
idrostatico.
 L’orografia determina totalmente la distribuzione della precipitazione
‘orografica’ e la ciclogenesi; i flussi superficiali sono relativamente
poco importanti.