Natural Hazards and Earth System Science www.nat-hazards-earth-syst-sci.net 1561-8633 1684-9981 8 6 2008 10.5194/nhess-8-1417-2008 http://www.nat-hazards-earth-syst-sci.net/8/1417/2008/ http://www.nat-hazards-earth-syst-sci.net/8/1417/2008/nhess-8-1417-2008.html http://www.nat-hazards-earth-syst-sci.net/8/1417/2008/nhess-8-1417-2008.pdf 1417 1430 2008-12-15 An observational and numerical study of a flash-flood event over south-eastern Italy M. M. Miglietta m.miglietta@isac.cnr.it A. Regano Institute of Atmospheric Sciences and Climate, Lecce, Italy now at: Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Rome, Italy A flash-flood episode affecting a small area in Apulia (south-eastern Italy) on 22 October 2005 is documented. A rainfall amount of 160 mm was recorded in a 6 h interval in the central part of the region, producing severe damage and causing six fatalities. Synoptic maps, observations from surface stations and remote-sensing data are used here to describe the evolution of the rainfall system. The vertical profiles show features similar to those observed in other orographic heavy-rain events, such as a low-level jet, a conditionally unstable environment, and a nearly saturated warm low-level air mass. The low hills in the centre of the region play an important role in the release of the instability and the localisation of the rainfall, providing the uplift necessary to the air parcels to reach the level of free convection. Numerical simulations are performed in order to understand the mechanisms responsible for the heavy rain event. The Weather Research and Forecasting model (WRF) is setup in a 2-way nesting configuration including two domains. The model is able to realistically simulate the evolution of the precipitation system and to capture fairly well the localisation, the amount and the timing of the rainfall. The simulations suggest the important synergy of low and upper-tropospheric features which act as the triggering mechanism for the development of convection. A sensitivity experiment confirms the importance of the orography for the development of convective cells. Anquetin, S., Creutin, J D., Delrieu, G., Ducrocq, V., Gaume, E., and Ruin, I.: Increasing the forecasting lead-time of Weather driven Flash-floods, Joint Research Center, Institute for Environment and Sustainability, H01/812/02/D9056/AG/ct, 33~pp., 2004. Baldassare, G. and Francescangeli, R.: Osservazioni e considerazioni sulla inondazione del 6 novembre 1926 in Bari e su un relativo deposito, Memorie Società Geologica Italiana, 37, 7–16, 1987. Bauer, M H., Mayr, G J., Vergeiner, I., and Pichler, H.: Strongly nonlinear flow over and around a three-dimensional mountain as a function of the horizontal aspect ratio, J. Atmos. Sci., 57, 3971–3991, 2000. Bellecci, C., Colacino, M., and Federico, S.: Quantitative precipitation of the Soverato flood: the role of orography and surface fluxes, Il Nuovo Cimento C, 26C, 7–22, 2003. Buzzi, A., Richard, E., and Romero, R.: Summary report on MEDEX studies and scientific results on Mediterranean cyclones causing high impact weather, Report on scientific results, available at: http://medex.aemet.uib.es/documents/Summary_on_MEDEX_studies_Nov05.pdf, 2005. Byers, H R. and Braham, R R.: The thunderstorm, US Government Printing Office, Washington, DC, 287~pp., 1949. Chappell, C F.: Quasi-stationary convective events, in: Mesoscale Meteorology and Forecasting, edited by: Ray, P S., The American Meteorological Society Ltd., 289–310, 1986. Chu, C.-M. and Lin, Y.-L.: Effects of orography on the generation and propagation of mesoscale convective systems in a two-dimensional conditionally unstable flow, J. Atmos. Sci., 57, 3817–3837, 2000. Daley, R.: Atmospheric Data Analysis, Cambridge University Press, Cambridge, 480~pp., 1991. Doswell~III, C A.: The distinction between large-scale and mesoscale contribution to severe convection: A case study example, Weather Forecast., 2, 3–16, 1987. Emanuel, K A.: An air-sea interaction model of intraseasonal oscillations in the tropics, J. Atmos. Sci., 44, 2324–2340, 1987. Federico, S., Avolio, E., Bellecci, C., Lavagnini, A., Colacino, M., and Walko, R L.: Numerical analysis of an intense rainstorm occurred in southern Italy, Nat. Hazards Earth Syst. Sci., 8, 19–35, 2008. Fehlmann, R., Quadri, C., and Davies, H C.: An Alpine rainstorm: Sensitivity to themesoscale upper-level structure, Weather Forecast., 15, 4–28, 2000. Gozzini, B., Maracchi, G., Meneguzzo, F., and Niccolai, M.: The catastrofic flood occurred in Versilia basin, Tuscany, on 19th June 1996: a way to predictability, in: RIBAMOD (river basin modelling, management and flood mitigation, Concerted Action) Proceedings of the first workshop, edited by: Casale, R., Pedroli, G B., and Samuels, P., Delft (Netherlands), 13–15 February 1997, 211–228, 1998. Guzzetti, F., Cardinali, M., and Reichenbach, P.: The AVI project: A bibliographical and archive inventory of landslides and floods in Italy, Environ. Manage., 18, 623–633, 1994. Horvath, K., Fita, L., Romero, R., Ivanèan-Picek, B., and Stiperski, I.: Cyclogenesis in the lee of the Atlas Mountains: a factor separation numerical study, Adv. Geosci., 7, 327–331, 2006. Hoskins, B J., McIntyre, M E., and Robertson, A W.: On the use and significance of isentropic potential vorticity maps, Q. J. Roy. Meteor.\ Soc., 111, 877–946, 1985. Intergovernmental Panel on Climate Change (IPCC): Climate Change 2007: The Physical Science Basis, edited by: Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K B., Tignor, M., and Miller, H L., Cambridge University Press, Cambridge, UK and New York, NY, USA, 996~pp., 2007. Kalnay, E. and Coauthors: The NCEP/NCAR 40-Year Reanalysis Project, B. Am.\ Meteorol. Soc, 77, 437–471, 1996. Krichak, S O., Alpert, P., and Dayan, M.: A southeastern Mediterranean PV streamer and its role in December 2001 case with torrential rains in Israel, Nat. Hazards Earth Syst. Sci., 7, 21–32, 2007. Lin, Y.-L., Chao, S., Wang, T A., Kaplan, M L., and Weglarz, R P.: Some common ingredients for heavy orographic rainfall, Weather Forecast., 16, 633–660, 2001. Marshall, J S. and Palmer, W M.: The distribution of raindrops with size, J. Meteorol., 5, 165–166, 1948. Massacand, A C., Wernly, H., and Davies, H C.: Heavy precipitation on the Alpine south-side: An upper-level precursor, Geophys. Res. Lett., 25, 1435–1438, 1998. Michalakes, J., Dudhia, J., Gill, D., Henderson, T., Klemp, J., Skamarock, W., and Wang, W.: The Weather Research and Forecast Model: Software Architecture and Performance, in: 11th ECMWF Workshop on the Use of High Performance Computing, in: Meteorology, Reading UK, edited by: Zwieflhofer, W. and Mozdzynski, G., World Scientific, 156–168, 2005. Miglietta, M M. and Buzzi, A.: A numerical study of moist stratified flows over isolated topography, Tellus~A, 53, 481–499, 2001. Miglietta, M M. and Rotunno, R.: Numerical simulations of conditionally unstable flows over a ridge, in: International Conference on Alpine Meteorology, Chambéry, France, 4–8 June 2007, 1, 87–90, 2007. Moscatello, A., Miglietta, M M., and Rotunno, R.: Observational analysis of a Mediterranean `hurricane' over south-eastern Italy, Weather, 63, 306–311, 2008. Pontrelli, M D., Bryan, G., and Fritsch, J M.: The Madison County, Virginia, Flash Flood of 27 June 1995, Weather Forecast., 14, 384 404, 1999. Regano, A.: Dall'assimilazione dei dati all'analisi meteorologica, Ph.D thesis, University of Bari, 2007. Simmons, A J.: Development of a high-resolution, sami-Lagrangian version of the ECMWF forecast model, Numerical Methods in Atmospheric Models, European Centre for Medium Range Forecasts, 2, 281–324. Skamarock, W C., Klemp, J B., Dudhia, J., Gill, D O., Barker, D M., Wang, W., and Powers, J G.: A description of the Advanced Research WRF Version~2, NCAR Tech. Note~468STR, 88~pp., 2005. Stein, J.: Exploration of some convective regimes over the Alpine orography, Q. J. Roy. Meteor. Soc., 130, 481–502, 2004. Stein, U. and Alpert, P.: Factor separation in numerical simulations, J.\ Atmos. Sci., 50, 2107–2115, 1993. Smith, R B.: The influence of mountains on the atmosphere, Adv. Geophys., Academic Press, 21, 87–230, 1979. Thorpe, A J.: Diagnosis of balanced vortex structure using potential vorticity, J. Atmos. Sci., 42, 397–406, 1985. Tripoli, G J., Medaglia, C M., Dietrich, S., Mugnai, A., Panegrossi, G., Pinori, S., and Smith, E A.: The 9–10 November 2001 Algerian flood: a numerical study, B. Am. Meteorol. Soc., 1229–1235, 2005. Wicker, L J. and Skamarock, W C.: Time splitting methods for elastic models using forward time schemes, Mon. Weather Rev., 130, 2088–2097, 2002.