Connecting flash flood events with radar-derived convective storm characteristics on the northwestern Mediterranean coast: knowing the present for better future scenarios adaptation

The northwestern Mediterranean coast is one of the areas most affected by flash floods and adverse weather, where also global climate scenarios are predicting an increase in precipitation extremes. This, along with the sea-level rise and the associated potential infrastructure and economical losses, represents a major risk for coastal settlements, as the one studied in this work: a major touristic area on the southern coast of Catalonia. The objective of the present paper is, thus, to understand in-depth the behavior of convective activity in the area and its link with flash flood events, to improve adverse and severe weather early warning systems in a rapidly changing weather as an adaptation measure. With this purpose, the study focuses on the period 2014–2018, analyzing the convective cells and storm motion in the region of study, through the new identification and tracking algorithm developed by the authors and applied in the Meteorological Service of Catalonia. The results show that the area is mostly affected by shallow but efficient convection, probably embedded in major weather systems with high precipitation rain rates, which tends to saturate the catchments and produce flooding. The work also shows the role of the topography as a triggering factor for storms outside the convective season, as a key feature for the convergence lines organization, and as a capping for stationary cells upstream. Improvements in the current warning system, such as different precipitation thresholds considering the time of exposure to that rain, as well as a further study are also presented as main results. These results can be extrapolated and applied to other regions affected by the same kind of heavy precipitation and flash floods.