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)

FLOOD 66 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. Firenze Dolomiti bellunesi Grosseto Venezia

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.

Tuscany (Arno and Ombrone River basins) §extreme event for precipitation intensity, extension and continuity – most of the rain fell on 4 November

The Eastern Alps (Adige and other river basins) Most of precip. fell 3-4 November)

Z500 T L 511L60 analysis: 12 UTC of 1-4 November This figure shows the T L 511L60 analyses at 12UTC of 1-4 November. Contour interval is 4dam.

ERA40 and T L 511L60 analyses: 12 UTC of 1-2 November The ERA-40 (T L 159L60, left) and the T L 511L60 (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 high- resolution (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 T L 511L60 deterministic forecasts for 3-4 Nov (168h, 120h, 72h) This figure shows T L 511L60 forecasts of 24h-accumulated precipitation started at 12UTC of the 27 ( h) and 29 ( h) October, and 1 November (48-72h) and valid for 3-4 November. The right-bottom panel shows a proxi for verification defined by the T L 511L60 24h forecast started at 12UTC of 3 November. Contour isolines are mm for precipitation. t+48-72h t h t h 3-4 Nov

24h TP: EPS fc from 30 Oct for 3-4 Nov (96-120h) This figure shows three EPS (51*T L 255L40) 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 T L 511L40 24h forecast started on 3 November. Contour isolines are % for probabilities and mm for precipitation. P(TP>75mm) P(TP>25mm) P(TP>50mm) 3-4 Nov Good EPS t h fc over Friuli for all thresholds, and some signals that 75mm could hit also Tuscany …

24h TP: EPS fc from 31 Oct for 3-4 Nov (72-96h) This figure shows three EPS (51*T L 255L40) 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 T L 511L40 24h forecast started on 3 November. Contour isolines are % for probabilities and mm for precipitation. P(TP>75mm) P(TP>25mm)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.. 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) This figure shows three EPS (51*T L 255L40) probabilistic forecasts started on 30 October ( h) 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 T L 511L40 24h forecast started on 3 November. Contour isolines are % for probabilities and mm for precipitation. P(TP>75mm) P(TP>25mm) P(TP>50mm) 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 (60 km) 12 UTC 1 Nov 66 2 nov4 nov3 nov BOLAM 18 km BOLAM 6 km Accumulated precipitation period MOLOCH 2 km 5 nov 06 UTC 3 Nov 06 UTC 5 Nov 00 UTC 2 Nov 00 UTC 3 Nov Rianalisi ECMWF (60 km) 12 UTC 1 Nov 66 2 nov4 nov3 nov BOLAM 18 km BOLAM 6 km Accumulated precipitation period MOLOCH 2 km 5 nov 06 UTC 3 Nov 06 UTC 5 Nov 00 UTC 2 Nov 00 UTC 3 Nov Rianalisi ECMWF (T511, 45 km) 12 UTC 1 Nov 66 2 nov 4 nov 3 nov BOLAM 18 BOLAM 6 km Accumulated precipitation period MOLOCH 2 km 5 nov 06 UTC 3 Nov 06 UTC 5 Nov 00 UTC 2 Nov 00 UTC 3 Nov

The BOLAM 6km precipitation forecast

The MOLOCH 2 km precipitation forecast

The MOLOCH 2 km precipitation forecast but starting with the NCEP reanalysis (300 km!)

ECMWFNCEP Short digression about ECMWF vs NCEP reanalyses …

ECMWFNCEP

ECMWFNCEP

ECMWFNCEP

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

Isarco a Chiusa A=3059 km² Adige a Trento A=9763 km² Noce a S.Giustina A=1050 km² Avisio a Lavis A=934 km² Adige a Bronzolo A=6926 km² Simulazioni idrologiche

Esempio di risultato della modellistica idrologica (Univ. di Brescia)

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 > 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.