Evolution of the modelling strategy within the Vilaine and Breton coastal streams flood forecasting service and consequences on the flood alert production

The Vilaine and Breton coastal streams flood forecasting service (SPC VCB) is responsible of the flood alert production on the Brittany territory. How did the modelling strategy within the SPC VCB evolve over time and which consequences these evolutions had on the flood alert production? To answer this question, all models used by the SPC VCB were classified in three categories: statistic, hydrodrologic and hydraulic. Conformity of the prevision points were compared for each hydrological year in order to evaluate the impact of the modelling development on the forecasting performance. Those data reveal a diversification of the models category over time. In 2014, only statistic models were used. Nowadays, 59.7% of model outputs come from statistic models, 34% come from hydrologic models and 6.3% come from hydraulic models. The mean annual conformity constantly increased, from 52.6% in 2007-2011 to 74.5% in 2019-2023. The modelling strategies took part in the flood alert improvement.