CIMA Research Foundation


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Rebora N.,CIMA Research Foundation | Molini L.,CIMA Research Foundation | Casella E.,University of Genoa | Comellas A.,University of Genoa | And 6 more authors.
Journal of Hydrometeorology | Year: 2013

Flash floods induced by extreme rainfall events represent one of the most life-threatening phenomena in the Mediterranean. While their catastrophic ground effects are well documented by postevent surveys, the extreme rainfall events that generate them are still difficult to observe properly. Being able to collect observations of such events will help scientists to better understand and model these phenomena. The recent flash floods that hit the Liguria region (Italy) between the end of October and beginning of November 2011 give us the opportunity to use the measurements available from a large number of sensors, both ground based and spaceborne, to characterize these events. In this paper, the authors analyze the role of the key ingredients (e.g., unstable air masses, moist low-level jets, steep orography, and a slow-evolving synoptic pattern) for severe rainfall processes over complex orography. For the two Ligurian events, this role has been analyzed through the available observations (e.g., Meteosat Second Generation, Moderate Resolution Imaging Spectroradiometer, the Italian Radar Network mosaic, and the Italian rain gauge network observations). The authors then address the possible role of sea-atmosphere interactions and propose a characterization of these events in terms of their predictability. © 2013 American Meteorological Society.

Molini L.,CIMA Research Foundation | Parodi A.,CIMA Research Foundation | Rebora N.,CIMA Research Foundation | Craig G.C.,Ludwig Maximilians University of Munich
Quarterly Journal of the Royal Meteorological Society | Year: 2011

Raingauge data over Italy for the period January 2006-February 2009 have been used to classify severe rainfall events into two types using a recently developed methodology. The types are defined as either long-lived and spatially distributed (Type I) if lasting more than 12 h and larger than 50 × 50 km2 or brief and localized (Type II) if having shorter duration or smaller spatial extent. A total of 81 events were identified, with 51 classified as Type I and 30 as Type II. The work presented here examines the hypothesis that the two types of event are associated with different dynamical regimes distinguished by differing degrees of control of convective precipitation by the synoptic-scale flow. For each of the 81 events, a time-scale for convective adjustment is computed, based on gridded hourly precipitation rates derived from rain-gauge data and ECMWF analysis (ERA-Interim) of convective available potential energy (CAPE). Values of the convective adjustment time-scale, τc, shorter than 6 h indicate convection that is responding rapidly to to the synoptic environment (equilibrium), while slower time-scales indicate that other, presumably local, factors dominate. It was anticipated that τc > 6 h would correspond to brief and localized Type II events, while τc < 6 h would indicate Type I events. This hypothesis was largely confirmed, with 45 of the 51 Type I events having time-scales shorter than 6 h and 20 of the 30 Type II events having time-scales longer than 6 h. © 2011 Royal Meteorological Society.

Silvestro F.,CIMA Research Foundation | Rebora N.,CIMA Research Foundation | Ferraris L.,CIMA Research Foundation | Ferraris L.,University of Genoa
Journal of Hydrometeorology | Year: 2011

The forecast of rainfall-driven floods is one of the main themes of analysis in hydrometeorology and a critical issue for civil protection systems. This work describes a complete hydrometeorological forecast system for small- and medium-sized basins and has been designed for operational applications. In this case, because of the size of the target catchments and to properly account for uncertainty sources in the prediction chain, the authors apply a probabilistic framework. This approach allows for delivering a prediction of streamflow that is valuable for decision makers and that uses as input quantitative precipitation forecasts (QPF) issued by a regional center that is in charge of hydrometeorological predictions in the Liguria region of Italy. This kind of forecast is derived from different meteorological models and from the experience of meteorologists. Single-catchment and multicatchment approaches have been operationally implemented and studied. The hydrometeorological forecasting chain has been applied to a series of case studies with encouraging results. The implemented system makes effective use of the quantitative information content of rainfall forecasts issued by expert meteorologists for flood-alert purposes. © 2011 American Meteorological Society.

Parodi A.,CIMA Research Foundation | Tanelli S.,Jet Propulsion Laboratory
Journal of Geophysical Research: Atmospheres | Year: 2010

In this work, deep moist convective processes, observed during the Tropical Composition, Cloud and Climate Coupling Experiment (TC4) over the East Pacific Intertropical Convergence Zone, were modeled by means of high-resolution numerical simulations with the Weather Research and Forecasting model. Three different turbulence parameterizations and two microphysical parameterizations are used. Their impact on the spatio-temporal structure of predicted convective fields is compared to TC4 observations from a geostationary imager, airborne precipitation radar, and dropsondes. It is found that the large-eddy simulation turbulence closure "upscaled" to the terra incognita range of grid spacings (i.e., 0.1-1 km) is best suited to model the deep convective processes under examination. © Copyright 2010 by the American Geophysical Union.

Parodi A.,CIMA Research Foundation | Foufoula-Georgiou E.,University of Minnesota | Emanuel K.,Massachusetts Institute of Technology
Journal of Geophysical Research: Atmospheres | Year: 2011

Previous studies have suggested that the statistical multiscale structure of rainfall can be parameterized in terms of thermodynamic descriptors of the storm environment, and such dependence has been successfully implemented in downscaling applications. In this paper we suggest that it is possible to adopt the raindrop terminal velocity as a physical parameter to explain to a large degree the statistical variability of convective rainfall over a range of scales. We examine this assertion by analysis of high-resolution simulations of an atmosphere in radiative-convective equilibrium performed using the Weather Research and Forecasting (WRF) model and prescribing different rain terminal velocity settings corresponding to small, slowly falling drops and large, quickly falling drops, respectively. The analysis has focused on the study of the dependence of some basic statistics of rainfall fields (probability distribution of convective rain cell areas, power spectra, and multiscale statistics of rainfall intensity) on the raindrop terminal velocity by using a well-documented and widely used atmospheric model. Possible applications of our results include downscaling of rainfall satellite measurements, conditional on limited microphysical information from dual-frequency spaceborne radars, and conversion of radar reflectivity to rain rate, conditional on drop size distribution inferred from the scaling parameters of the reflectivity fields. Copyright 2011 by the American Geophysical Union.

Fiori E.,CIMA Research Foundation | Parodi A.,CIMA Research Foundation | Siccardi F.,CIMA Research Foundation | Siccardi F.,University of Genoa
Atmospheric Research | Year: 2011

A line of development of numerical meteorological forecast, common to many European and American Meteorological Organizations, schedules a drastic reduction of the grid spacing for the realization of limited-area predictions.The scientific community has been discussing such an issue whether this approach can be of real advantage for the solution of the problems of the uncertainty of the decision-maker. The extraordinary enhancement of the computer power could indeed promote this drastic reduction of the modeling horizontal resolution just because "nowadays it is possible". However this "brute-force" approach to the question of the solution of the problem of nowcasting does not guarantee a priori improvement of forecast skill.In this framework, deep moist convective processes in simplified atmospheric scenarios (e.g. supercell) are studied in this paper by means of high-resolution numerical simulations with COSMO-Model.Particular attention is paid to determine whether and at which extent the convection-resolving solutions, in the range of grid spacing between 1. km and 100. m, statistically converge from a turbulence perspective with respect to flow field structure, transport properties and precipitation forecast. Different turbulence closures, microphysics settings and grid spacings are combined and their joint impact on the spatial-temporal properties of storm processes is discussed. © 2010 Elsevier B.V.

Ghizzoni T.,Corporate Underwriting Geo Risks | Roth G.,University of Genoa | Rudari R.,CIMA Research Foundation
Journal of Hydrology | Year: 2012

This contribution presents an assessment of the joint probability distribution able to describe multi-site multi-basin flood scenarios in a high dimensionality framework. This goal will be pursued through two different approaches: the multivariate skew-t distribution and the Student copula with arbitrary margins. While copulas have been widely used in the modeling of hydrological processes, the use of the skew-t distribution in hydrology has been only recently proposed with reference to a trivariate application (Ghizzoni et al., 2010, Adv. Water Resour., 33, 1243-1255). Both methods are here applied and discussed in a context of considerably higher dimensionality: the Upper Mississippi River floods. In fact, to enhance the characteristics of the correlation structure, eighteen nested and non-nested gauging stations were selected, with significantly different contributing areas. Such conditions represent a challenge for both the skew-t and the copula approach. In perspective, the ability of such approaches in explaining the multivariate aspects of the relevant processes is needed to specify flood hazard scenarios in terms of their intensity, extension and frequency. When this is associated to the knowledge of location, value and vulnerability of exposed elements, comprehensive flood risk scenarios can be produced, and risk cumuli quantified, for given portfolios, composed of wherever located risks. © 2011 Elsevier B.V.

Pinto J.G.,University of Cologne | Ulbrich S.,University of Cologne | Parodi A.,CIMA Research Foundation | Rudari R.,CIMA Research Foundation | And 2 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2013

An objective identification and ranking of extraordinary rainfall events for Northwest Italy is established using time series of annual precipitation maxima for 1938-2002 at over 200 stations. Rainfall annual maxima are considered for five reference durations (1, 3, 6, 12, and 24 h). In a first step, a day is classified as an extraordinary rainfall day when a regional threshold calculated on the basis of a two-components extreme value distribution is exceeded for at least one of the stations. Second, a clustering procedure taking into account the different rainfall durations is applied to the identified 163 events. Third, a division into six clusters is chosen using Ward's distance criteria. It is found that two of these clusters include the seven strongest events as quantified from a newly developed measure of intensity which combines rainfall intensities and spatial extension. Two other clusters include the weakest 72% historical events. The obtained clusters are analyzed in terms of typical synoptic characteristics. The two top clusters are characterized by strong and persistent upper air troughs inducing not only moisture advection from the North Atlantic into the Western Mediterranean but also strong northward flow towards the southern Alpine ranges. Humidity transports from the North Atlantic are less important for the weaker clusters. We conclude that moisture advection from the North Atlantic plays a relevant role in the magnitude of the extraordinary events over Northwest Italy. © 2013. American Geophysical Union. All Rights Reserved.

Tepsich P.,CIMA Research Foundation | Rosso M.,CIMA Research Foundation | Halpin P.N.,Duke University | Moulins A.,CIMA Research Foundation
Marine Ecology Progress Series | Year: 2014

We used generalized additive models (GAMs) as exploratory habitat models for describing the distribution of 2 deep-diving species, Cuvier's beaked whale Ziphius cavirostris Cuvier, 1823 and sperm whale Physeter catodon Linnaeus, 1758, in the Pelagos Sanctuary (northwestern Mediterranean). We analyzed data collected from research surveys and whale-watching activities during summer months from 2004 to 2007. The dataset encompassed 147 Cuvier's beaked whale sightings and 52 sperm whale sightings. We defined and applied a post hoc workflow to the data, to minimize false absence bias arising from the unique ecology of the species and the lack of a dedicated sampling design. We calculated a novel topographic predictor, distance from the canyon axis, as a covariate for use in the habitat model. Given the complex topography of the area, the analysis was performed on a high-resolution spatial grid (1 km). Our methods allowed effective use of the non-dedicated sampling dataset for building habitat models of elusive and cryptic species (Cuvier's beaked whale final model sensitivity = 0.88 and specificity = 0.84; sperm whale final model sensitivity = 0.65 and specificity = 0.77). The GAM results confirmed the preference for submarine canyons for both species and also highlighted the importance of the deeper portion of the Ligurian basin, especially for Cuvier's beaked whale. Habitat overlap nevertheless is resolved by a well-defined spatial partitioning of the area, with sperm whale occupying the western part and Cuvier's beaked whale the central and eastern parts. © Inter-Research 2014.

Silvestro F.,CIMA Research Foundation | Rebora N.,CIMA Research Foundation
Journal of Hydrology | Year: 2014

One of the main difficulties that flood forecasters are faced with is evaluating how errors and uncertainties in forecasted precipitation propagate into streamflow forecast. These errors, must be combined with the effects of different initial soil moisture conditions that generally have a significant impact on the final results of a flood forecast. This is further complicated by the fact that a probabilistic approach is needed, especially when small and medium size basins are considered (the variability of the streamflow scenarios is in fact strongly influenced by the aforementioned factors). Moreover, the ensemble size is a degree of freedom when a precipitation downscaling algorithm is part of the forecast chain. In fact, a change of ensemble size could lead to different final results once the other inputs and parameters are fixed. In this work, a series of synthetic experiments have been designed and implemented to test an operational probabilistic flood forecast system in order to augment the knowledge of how streamflow forecasts can be affected by errors and uncertainties associated with the three aforementioned elements: forecasted rainfall, soil moisture initial conditions, and ensemble size. © 2014 The Authors.

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