The Piemonte Region Meteo-hydrological Alert Procedure and the Real Time Physically-Based Flood Forecasting System

The development and implementation of a real-time Flood Forecasting System in the context of the Piemonte Region's Meteo-hydrological Alert Procedure is described. The area of interest is the Upper Po River basin (Northwest Italy) of approximately 37000 km2 and its river network of about 3000 Km and 3 big lakes. FloodWatch, a GIS-based decision support system for real-time flood forecasting has been developed since January 2000. It has been installed and operationally used at the Piemonte Region's Room for the Situation of Natural Hazards in Torino, Italy. FloodWatch simulations are based on MIKE 11 modules which provide a continuous lumped hydrological modeling of 187 tree-structured subcatchments connected by a 1D distributed hydrodynamic model. It is directly linked to the telemetric gauges system, which provides measured data from more than 300 meteorological (rainfall and temperature) and about 100 water level stations. In addition, FloodWatch uses quantitative precipitation and temperature forecasts daily issued by the Regional Meteorological Service on the 11 zones in which the study area is subdivided. At present, FloodWatch automatically supplies operational forecasts of water-level and discharge at 73 locations for up to 48 hours. The development of a fast and reliable flow forecasting system for this large and heterogeneous river basin required careful balance between the need for rapid and accurate forecasts and of a correct representation of run- off generation, flood propagation, baseflows, snow accumulation and melting. Strengths and limits of the system are focused addressing the need for future development. Some results are presented with particular regard to the October 2000 flood event, when the northwest of Italy experienced one of the largest floods on record. Heavy and prolonged rainfall fell across the entire Po river basin. The flood inundated vast areas causing widespread damage and thousands of people were warned and alerted to evacuate.