Severe floods predictive ability: A proxy based probabilistic assessment of the Italian early warning system

In compliance with the national legal framework, the regional offices (CFDs) of the Italian Civil Protection Department have the daily duty to issue warn- ings to the local population on the account of the weather and hydrology- related impacts, predicted by forecast models and refined through their exper- tise and experience: this composite of objective (model) and subjective (ana- lyst) assessments are both contributing to the actual colour-coded warning system. Given its hybrid nature, it is of paramount importance to evaluate the predictive ability of the warning decision-making process as a whole. To this end, this study compares the return period T of the occurred flood (estimated through an hydrological model fed with observations) to the warning level that was issued. The novelty of this approach is that, by applying this methodology extensively in space and time, the probability curves of the variable T for each warning level are computed, allowing to evaluate the consistency between the warnings and the actual (estimated) severity of the event. As results suggest, the national early warning system is proven to be overall reliable for most cases, though very fine scale events (e.g., severe, localised, short-lived thunder- storms) are still an open challenge.