Abstract. In recent years, the interest in the prediction and prevention of natural hazards related to hydrometeorological events has grown due to the increased frequency of extreme rainstorms. Several research projects have been developed to test hydrometeorological models for real-time flood forecasting. However, flood forecasting systems are still not widespread in operational context. Real-world examples are mainly dedicated to the use of flood routing model, best suited for large river basins. For small basins, it is necessary to take advantage of the lag time between the onset of a rainstorm and the beginning of the hydrograph rise, with the use of rainfall-runoff transformation models. Nevertheless, when the lag time is very short, a rainfall predictor is required, as a result, meteorological models are often coupled with hydrological simulation. While this chaining allows floods to be forecasted on small catchments with response times ranging from 6 to 12 h it, however, causes new problems for the reliability of Quantitative Precipitation Forecasts (QPF) and also creates additional accuracy problems for space and time scales.The aim of this work is to evaluate the degree to which uncertain QPF affects the reliability of the whole hydrometeorological alert system for small catchments. For this purpose, a distributed hydrological model (FEST-WB) was developed and analysed in operational setting experiments, i.e. the hydrological model was forced with rain observation until the time of forecast and with the QPF for the successive period, as is usual in real-time procedures. Analysis focuses on the AMPHORE case studies in Piemonte in November 2002.

The Piemonte regional warning system service, managed by the Environmental Protection Agency of Piemonte ("ARPA Piemonte" as official Italian acronym), is based on an advanced meteo-hydrological automatic monitoring system, and it is integrated with forecasting activities of severe weather-related natural hazards. At present, a meteo-hydrological chain is operated to provide flood forecasting on the main river pattern. The development of a forecasting tool for shallow landslides triggered by heavy rainfall is presented. Due to the difficulties in modelling shallow landslides triggering in a large and complex area like the Piemonte region, an empirical model is developed on the basis of the correlation between rainfall and previous landslides in historical documents. The research focuses on establishing rainfall thresholds for landslides triggering, differentiating the critical rainfall values through a geological characterisation of the different territories. The period from 1990 to 2002 is considered. A total number of 160 landslides with hourly information and time of triggering are used to calibrate the system. As a first outcome, two different zones have been identified: (1) zones in alpine environments, principally characterised by a bedrock composed of metamorphic rocks, igneous rocks, dolostones or limestones that require high values of critical rainfall and (2) zones in hilly environments, principally characterised by sedimentary bedrock that require low values of critical rainfall. Verification has been performed on a total number of 429 landslides with known date of occurrence. The results show a good agreement with the model with no missed alarms and a very low number of false alarms, thus suggesting an effective operational implementation.

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Abstract:A raster-based glacier sub-model was successfully introduced in the distributed hydrological model FEST-WB to simulate the water balance and surface runoff of large Alpine catchments. The glacier model is based on temperature-index approach for melt, on linear reservoir for melt water propagation into the ice and on mass balance for accumulation; the initialization of the volume of ice on the basin was based on a formulation depending on surface topography. The model was first tested on a sub-basin of the Rhone basin (Switzerland), which is for 62% glaciated; the calibration and validation were based on comparison between simulated and observed discharge from 1999 to 2008. The model proved to be suitable to simulate the typical discharge seasonality of a heavily glaciated basin. The performance of the model was also tested by simulating discharge in the whole Swiss Rhone basin, in which glaciers contribution is not negligible, in fact, in summer, about the 40% of the discharge is due to glacier melt. The model allowed to take into account the volume of water coming from glaciers melt and its simple structure is suitable for analysis of the effects of climate change on hydrological regime of high mountain basins, with available meteorological forcing from current RCM.

The development and implementation of a real-time flood forecasting system in the context of the Piemonte Regions hydro-meteorological operational alert procedure is described. The area of interest is the Upper Po River basin (north-west Italy) of approximately 37 000 km 2 and its river network of about 3000 km and three big lakes. FloodWatch, a GIS-based decision support system for real-time flood forecasting, has been developed and used operationally at the Piemonte Regions Room for the Situation of Natural Hazards in Torino, Italy, since January 2000. The system is linked directly to the telemetric gauges system, uses daily quantitative precipitation and temperature forecasts issued by the Regional Meteorological Service and automatically supplies operational forecasts of water-level and discharge at about 30 locations for up to 48 hours. Strengths and limits of the system and its link with operational flood alert and management are discussed. The case study presented is the October 2000 flood event, when the north-west of Italy experienced one of the largest floods on record. Results highlight how the uncertainty linked to the use of meteorological forecasts greatly influences the quality of the hydrological forecasts. The proposed alert procedure, based on coded risk levels, can help effectively in facing forecast uncertainties.