Abstract
The operational meteo-hydrological forecasting chain of the Liguria Region (NW Italy) is applied to a different morphoclimatic environment, such as the Emilia Romagna Region (N Italy). Modification to the chain, both in models and in procedures, are introduced to overcome problems related to medium dimension catchments (A≈1000 km 2 ), characterized by complex altimetry profiles and antropical interventions along the river. The main feature of the original operational procedure, that is the probabilistic approach, is maintained. Hydraulic hazard reduction through artificial reservoirs management is exploited with reference to a specific event occurred on the Reno basin (Emilia Romagna Region).
Introduction
The capability to predict in advance potentially critic meteorological events is one of the most important elements for civil protection (e.g. Siccardi, 1995; Direttiva PCM, 27/02/2004) .
Introduction
In this context, civil protection measures must refer to systems using rainfall forecast as input to drive hydrologic models as a viable alternative to the structural ways of reducing hydraulic hazards. In environments where more traditional structural measures (e.g. reservoir systems) are usually employed for flood hazard mitigation it is possible to increase lead-time through the use of a meteo-hydrological forecasting chain. The capability to predict land effects 24-48 h in advance is one of the most important elements in order to emptying artificial reservoirs, and consequently to have these volumes available to receive water flooding volumes.
Introduction
In this work the integrated meteo-hydrologic forecasting chain in use at the Centro Funzionale (CF) of Ligura region and at Centro di ricerca Interuniversitario in Monitoraggio Correspondence to: F. Giannoni (oduffy@example.net) Ambientale (CIMA) was modified in order to be applied to the context of the Reno river basin. The procedure is then applied to a case study of 8 November 2002. The possible benefits deriving from its implementation are discussed.
Meteo-hydrologic forecasting chain
The hydro-meteorological chain used in this work is based on the coupling of meteorological and hydrologic forecasts along the lines depicted in the following paragraphs. Meteorological forecasts are provided both by deterministic runs of the limited area model Lokal Modell and by the Limited-area Ensemble Prediction System (Molteni et al., 2001; Marsigli et al., 2001 ) in a probabilistic framework. Hydrological simulations are performed by applying the DRiFt model (Giannoni et al., 2005) .
Lokal Modell
The Lokal Modell of the COSMO Consortium (Doms and Schaettler, 1999 ) is a non-hydrostatic limited area atmospheric prediction model. It is designed for operational numerical weather prediction as well as for various scientific applications on the mesoscale (50-0.5 km). A variety of physical processes (radiation, turbulence, convection atmosphere-soil interaction) are taken into account by several parameterization schemes (Ritter and Geleyn, 1992; Jacobsen and Heise, 1989; Tiedtke, 1989) . The Lokal Modell offers different microphysical schemes spanning from the classical warm rain scheme (Kessler, 1969) to a graupel scheme.
Limited-area Ensemble Prediction System
The Limited-area Ensemble Prediction System (LEPS) has been developed by ARPA-SIM of Emilia-Romagna (Italy). In the modelling of intense rainfall events over complex orography the system joins, in a synergetic way, the capability of an ensemble to provide a forecast in a probabilistic framework with the benefits given by a limited area model (Lokal Modell). LEPS is based on the Ensemble Prediction System (EPS) of the European Centre for Medium-range Weather Forecasts. The methodology used to generate LEPS from EPS is presented and fully described by Molteni et al. (2001) and by Marsigli et al. (2001) . An ensemble size reduction technique, which allows the selection of five representative members (RMs) out of the global ensemble, is used. Subsequently, five Lokal Modell integrations at 10 km horizontal resolution are nested in the five RMs.
Disaggregation model
The downscaling model here used to fill the gap between meteorological and hydrological scales is a multifractal model based on a wavelets transform (Deidda et al., 2000) . The procedure for its operational application is shown in Ferraris et al. (2002) . The model disaggregates the volume forecasted by Lokal Modell and by each LEPS over a 256×256 km domain centred on the studied area of the Reno basin. For each forecast generated, 100 possible independent equally probable precipitation events with a resolution of 1×1 km and 1 h are generated.
Hydrologic model
DRiFt (Discharge River Forecast) is a linear, semi-distributed event model based on a geomorphologic approach. The model is focused on the efficient description of the drainage system in its essential parts: hillslopes and channel networks. These are addressed with two kinematic scales, which determine the base of the geomorphologic response of the basin. The morphologic module is coupled with a simple representation of soil infiltration properties (SCS-CN, 1985) . Dis- charge at any location along the drainage network is evaluated by applying the convultion integral of the time-variant Instantaneous Unit Hydrograph, which is represented by the expression:
Hydrologic model
where: B is the drainage basin above the specified location, M(t, x) is the runoff rate (mm·h −1 ) at time t and location x, d o (x) denotes the distance from x to the closest stream channel and d 1 (x) denotes the distance from x to the outlet of the basin specified by the region B. Runoff is assumed to move over hillslopes at a uniform velocity v o and through the channel system at velocity v 1 (see Giannoni et al., 2005) . In the present work, the DRiFt model, was modified in order to be able to consider the damping effect due to the dams and reservoirs characterizing the Reno river basin (see. par. 3). Figure 1 describes the reservoirs system for hydroelectrical purposes immediately upstream of Casalecchio (i.e. the section chosen for the hydrologic simulation). Table 1 describes the essential geometric and hydraulic characteristics of the reservoir system.
Modified hydrologic model
The modified DRiFt model takes advantage of the linearity in describing runoff routing processes. This characteristic, in fact, allows a simple way to represent the effect of dams and reservoirs on the hydrologic response. The hydrologic response, Q, at the basin scale is therefore estimated according to the scheme in Fig. 2 as follows: Q R is estimated according to specific characteristics of the reservoir.
Study case
In this work the forecasting chain has been applied to the event of 8-10 November 2003 in the Reno Basin. The Reno basin is one of the largest in Emilia-Romagna region (4930 km 2 ). It has a mountainous portion of 1050 km 2 at Casalecchio Chiusa section, average slope 3.7% and a wide valley portion. There are four reservoirs for hydroelectric production located in the mountainous part of the basin. These are connected each other, in particular Suviana reservoir collects water from Molino del Pallone and Pavana, that are themselves in series, while Brasimone is connected to Suviana through a pressure pipe. A fifth reservoir, Santa Maria, is located downstream Brasimone (see Fig. 1 and Table 1 ). The capability of the modified hydrological model in reproducing the catchment response has been first verified using recorded rainfall series to drive the model (Fig. 3) . Moreover, flood mitigation has been tested by performing a manoeuvre that reduces the filling of the two largest reservoirs Suviana and Pavana by a 20% and a 30% (this manoeuvre corresponds to the volume that could be effectively emptied with a 48 h lead-time). The forecast rainfall field through Lokal Modell of 6 November at 12:00 UTC is then used to drive DRiFt. This leads to an underestimation of the flood event due to the both incongruence among meteorological and hydrological scales, and the uncertainty in the positioning of the precipitating clusters.
Study case
To obtain a significant statistical sample, for each LEPS member, 100 possible independent equally probably precipitation fields have been simulated, using a multifractal model (Ferraris et al., 2002) . For each simulation class a probability of occurrence equal to the one associated to its LEPS member is attached. Results computed at Casalecchio, with the exceeding probability curve of the peak discharge conditioned to the precipitation volume in the target area, are therefore derived from the LEPS outputs. Figures 4-5 illustrate the peak discharge exceeding probability curves by performing and not performing the manoeuvre described.
Results and Conclusions
The results of the proposed procedure show the possibility of extending the meteo-hydrological chain, operationally used at CIMA and at Liguria Region CF, to a different morphology taking into account the possibility of hydrograph lamination to mitigate the effect of floods. In the study case a modest manoeuvre reduced the peak discharge value of about 100 m 3 s −1 . In the forecasting phase the possibility of performing reservoir manoeuvre allows us to reduce of the exceeding probability of the warning level (Fig. 5) .
Results and Conclusions
This work is the first step towards an integrated management of artificial reservoirs in an hydrometeorological risk mitigation context based on meteorological forecast. The proposed hydrological model is able to take into account the role of hydraulic structures -such as dams and reservoirs -in predicting flood rising and propagation. The results are promising and suggest that this approach can be a valuable contribution within an integrated support decision system.

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