Benchmarking 2D Shallow Water Models in complex casestudies: the 2017Mandra (Greece) flood

The number of studies based on the integrated flood modelling at the basin scale, meaning that hydrological and hydrodynamic flood processes are described entirely within the2D Shallow Water Equations(2D-SWEs), is growing quickly. However, there is a need to provide further evidence about the reliability of this approach in real-world case studies, highlighting the overall performance in terms of accuracy and computational times. In this paper, a numerical parallel codeis applied to reconstruct the catastrophic flash flood event occurred in November 2017 in Mandra (Greece). The challenges of this benchmark case study are: a) the computational domain is quite complex and is composed by two peri-urban catchments about 20 km(2) each, and the urban environment of Mandra; b) the rainfall distribution in space is characterized by significant heterogeneity, due to the orographic mechanism of the storm. The rainfall maps are recorded by the mobile weather radar of the National Observatory of Athens with space step equal to 150 m and time step equal to 2 min. Finally, the output of the 2D-SWE solver is compared with post-event field data, which consist of the flood maximum depth at 44 points distributed across the Mandra town, showing good predictive capabilities.