The Role of Meteorological Models in the Prediction of Weather Hazards – the European Approach

It is a matter of fact that the economic damage and the casualties provoked by extreme meteorological events have dramatically increased in the last few decades, and that, in the last 30 years, a remarkable part of this increment is caused by the increased frequency of extreme meteorological events. The reasons for such an increase are not simply related to the climatic changes, but also to the intensive exploitation of the land areas, like unauthorized building, diffuse urbanization, river canalization, intensive agriculture etc., which has made them much more vulnerable today than in the past. In this context, the use of advanced meteorological instruments could surely give help in the forecasting and in the prevention of extreme phenomena and of their consequences. However, the greatest improvement in extreme events prediction can be achieved by the use of numerical models, which constitute an essential means in the aim of improving both the forecast of the extreme events and the correlated hydrogeological risk assessment. The paper, after a short introduction on the numerical models, contains some considerations on the importance of land surface conditions and of surface layer parameterizations in order to produce a reasonably good prediction of some extreme dry (droughts or heat waves) and wet (floods) events. Among the surface layer parameterizations, the representation of the orographic influences on the atmospheric flow is quite important for estimating the quantity and the intensity of the precipitation. It is explained that for extreme wet events the final objective would be to couple high-resolution meteorological and hydrological models, creating a “meteo-hydrological chain”. A detailed discussion will examine the role of the seasonal meteorological predictions, with a part dedicated to the Ensemble Prediction System, and to their utility for forecasting the hydrological variables. Finally, a reflection in the last section is dedicated to the problem of the communication of meteorological and hydrological risks to the public.