Abstract. Computer power has grown to the point that very-fine-mesh mesoscale modelling is now possible. Going down through scales is clumsily supposed to reduce uncertainty and to improve the predictive ability of the models. This work provides a contribution to understand how the uncertainty in the numerical weather prediction (NWP) of severe weather events is affected by increasing the model grid resolution and by choosing a parameterization which is able to represent turbulent processes at such finer scales. A deep moist convective scenario, a supercell, in a simplified atmospheric setting is studied by mean of high resolution numerical simulations with COSMO-Model. Different turbulent closures are used and their impacts on the space-time properties of convective fields are discussed. The convective-resolving solutions adopting Large Eddy Simulation (LES) turbulent closure converge with respect to the overall flow field structure when grid spacing is properly reduced. By comparing the rainfall fields produced by the model on larger scales with those at the convergence scales it's possible to size up the uncertainty introduced by the modelling itself on the predicted ground effects in such simplified scenario.
Abstract. Forecast verification is a long-standing issue of the whole meteorologists' community. A common definition of a truly satisfying prediction skill has not been achieved so far. Even the definition of "event", due to its spatio-temporal discontinuity, is highly affected by uncertainty. Moreover, decision-making demands numerical weather prediction modellers to provide information about the "inner" uncertainty, i.e. the degree of uncertainty related to the choice of a specific setting of the model (microphysics, turbulence scheme, convective closure, etc.). Most European Mediterranean countries, due to dense development, steep coastal orography and short hydrological response time of the drainage basins, have to deal very frequently with flash floods and sudden shallow land sliding impacting on urban areas. Civil protection organizations are in place to issue early warnings in order to allow local authorities and population to take precautionary measures. To do so in Mediterranean catchments, hydrologists are required to use numerical rainfall predictions in place of rainfall observations on large European catchments. Estimating the measure of uncertainty is for this reason crucial. The goal of this work is to propose an objective evaluation of the performance of the currently operational weather prediction model COSMO-I7 over quite a long time period and to check forecast verification at different space-time scales by the comparison of predictions with observations. Due to large investments in the last years, in fact, Italy has built up one of the most dense hourly-reporting network of rain gauges. The network has a mean space density of about 1/100 km2, very similar to the horizontal resolution of currently operating limited area models. An objective procedure to identify and compare the extreme events of precipitation has been applied to the full set of rainfall observations and over the severe events forecast by COSMO-I7 and announced in official warnings by Italian Civil Protection Department. The procedure allows to classify rainfall events as long-lived and spatially distributed or as having a shorter duration and a minor spatial extent. We show that long-lived events are less affected by overall uncertainty than short-lived ones, yet the inner uncertainty of the event affects both.
Abstract. The right of a person to be protected from natural hazards is a characteristic of the social and economical development of the society. This paper is a contribution to the reflection about the role of Civil Protection organizations in a modern society. The paper is based in the inaugural conference made by the authors on the 9th Plinius Conference on Mediterranean Storms. Two major issues are considered. The first one is sociological; the Civil Protection organizations and the responsible administration of the land use planning should be perceived as reliable as possible, in order to get consensus on the restrictions they pose, temporary or definitely, on the individual free use of the territory as well as in the entire warning system. The second one is technological: in order to be reliable they have to issue timely alert and warning to the population at large, but such alarms should be as "true" as possible. With this aim, the paper summarizes the historical evolution of the risk assessment, starting from the original concept of "hazard", introducing the concepts of "scenario of event" and "scenario of risk" and ending with a discussion about the uncertainties and limits of the most advanced and efficient tools to predict, to forecast and to observe the ground effects affecting people and their properties. The discussion is centred in the case of heavy rains and flood events in the North-West of Mediterranean Region.
Abstract. This paper analyses the predictive ability of quantitative precipitation forecasts (QPF) and the so-called "poor-man" rainfall probabilistic forecasts (RPF). With this aim, the full set of warnings issued by the Meteorological Service of Catalonia (SMC) for potentially-dangerous events due to severe precipitation has been analysed for the year 2008. For each of the 37 warnings, the QPFs obtained from the limited-area model MM5 have been verified against hourly precipitation data provided by the rain gauge network covering Catalonia (NE of Spain), managed by SMC. For a group of five selected case studies, a QPF comparison has been undertaken between the MM5 and COSMO-I7 limited-area models. Although MM5's predictive ability has been examined for these five cases by making use of satellite data, this paper only shows in detail the heavy precipitation event on the 9–10 May 2008. Finally, the "poor-man" rainfall probabilistic forecasts (RPF) issued by SMC at regional scale have also been tested against hourly precipitation observations. Verification results show that for long events (>24 h) MM5 tends to overestimate total precipitation, whereas for short events (≤24 h) the model tends instead to underestimate precipitation. The analysis of the five case studies concludes that most of MM5's QPF errors are mainly triggered by very poor representation of some of its cloud microphysical species, particularly the cloud liquid water and, to a lesser degree, the water vapor. The models' performance comparison demonstrates that MM5 and COSMO-I7 are on the same level of QPF skill, at least for the intense-rainfall events dealt with in the five case studies, whilst the warnings based on RPF issued by SMC have proven fairly correct when tested against hourly observed precipitation for 6-h intervals and at a small region scale. Throughout this study, we have only dealt with (SMC-issued) warning episodes in order to analyse deterministic (MM5 and COSMO-I7) and probabilistic (SMC) rainfall forecasts; therefore we have not taken into account those episodes that might (or might not) have been missed by the official SMC warnings. Therefore, whenever we talk about "misses", it is always in relation to the deterministic LAMs' QPFs.
Abstract. An exponential improvement of numerical weather prediction (NWP) models was observed during the last decade (Lynch, 2008). Civil Protection (CP) systems exploited Meteo services in order to redeploy their actions towards the prediction and prevention of events rather than towards an exclusively response-oriented mechanism1. Nevertheless, experience tells us that NWP models, even if assisted by real time observations, are far from being deterministic. Complications frequently emerge in medium to long range forecasting, which are subject to sudden modifications. On the other hand, short term forecasts, if seen through the lens of criminal trials2, are to the same extent, scarcely reliable (Molini et al., 2009). One particular episode related with wrong forecasts, in the Italian panorama, has deeply frightened CP operators as the NWP model in force missed a meteorological adversity which, in fact, caused death and dealt severe damage in the province of Vibo Valentia (2006). This event turned into a very discussed trial, lasting over three years, and intended against whom assumed the legal position of guardianship within the CP. A first set of data is now available showing that in concomitance with the trial of Vibo Valentia the number of alerts issued raised almost three folds. We sustain the hypothesis that the beginning of the process of overcriminalization (Husak, 2008) of CPs is currently increasing the number of false alerts with the consequent effect of weakening alert perception and response by the citizenship (Brezntiz, 1984). The common misunderstanding of such an issue, i.e. the inherent uncertainty in weather predictions, mainly by prosecutors and judges, and generally by whom deals with law and justice, is creating the basis for a defensive behaviour3 within CPs. This paper intends, thus, to analyse the social and legal relevance of uncertainty in the process of issuing meteo-hydrological alerts by CPs. Footnotes: 1 The Italian Civil Protection is working in this direction since 1992 (L. 225/92). An example of this effort is clearly given by the Prime Minister Decree (DPCM 20/12/2001 "Linee guida relative ai piani regionali per la programmazione delle attivita' di previsione, prevenzione e lotta attiva contro gli incendi boschivi – Guidelines for regional plans for the planning of prediction, prevention and forest fires fighting activities") that, already in 2001, emphasized "the most appropriate approach to pursue the preservation of forests is to promote and encourage prediction and prevention activities rather than giving priority to the emergency-phase focused on fire-fighting". 2 Supreme Court of the United States, In re Winship (No. 778), No. 778 argued: 20 January 1970, decided: 31 March 1970: Proof beyond a reasonable doubt, which is required by the Due Process Clause in criminal trials, is among the "essentials of due process and fair treatment" 3 In Kessler and McClellan (1996): "Defensive medicine is a potentially serious social problem: if fear of liability drives health care providers to administer treatments that do not have worthwhile medical benefits, then the current liability system may generate inefficiencies much larger than the costs of compensating malpractice claimants".
Abstract. On the 4 November 2011 a flash flood event hit the area of Genoa with dramatic consequences. Such an event represents, from the meteorological and hydrological perspective, a paradigm of flash floods in the Mediterranean environment. The hydro-meteorological probabilistic forecasting system for small and medium size catchments in use at the Civil Protection Centre of Liguria region exhibited excellent performances for the event, by predicting, 24–48 h in advance, the potential level of risk associated with the forecast. It greatly helped the decision makers in issuing a timely and correct alert. In this work we present the operational outputs of the system provided during the Liguria events and the post event hydrological modelling analysis that has been carried out accounting also for the crowd sourcing information and data. We discuss the benefit of the implemented probabilistic systems for decision-making under uncertainty, highlighting how, in this case, the multi-catchment approach used for predicting floods in small basins has been crucial.
