Toward Street‐Level Nowcasting of Flash Floods Impacts Based on HPC Hydrodynamic Modeling at the Watershed Scale and High‐Resolution Weather Radar Data

TLDR

High‑performance computing now enables two‑dimensional shallow‑water equation models to simulate floods at the catchment scale rather than only the hydraulic scale. This study seeks to develop an operational flash‑flood nowcasting system that delivers street‑level impact warnings by integrating weather‑radar data into a single HPC 2D‑SWE framework combining watershed hydrology, flow dynamics, and urban flooding. The authors implement a calibrated HPC 2D‑SWE model that assimilates high‑resolution radar rainfall to predict the timing, location, and intensity of street‑level hazards, illustrated using the 15 Nov 2017 Mandra flood event. The case study demonstrates the feasibility and accuracy of the approach, offering new insights for flash‑flood nowcasting research.

Abstract

Abstract In our era, the rapid increase of parallel programming coupled with high‐performance computing (HPC) facilities allows for the use of two‐dimensional shallow water equation (2D‐SWE) algorithms for simulating floods at the “hydrological” catchment scale, rather than just at the “hydraulic” fluvial scale. This approach paves the way for the development of new operational systems focused on impact‐based flash‐floods nowcasting, wherein hydrodynamic simulations directly model the spatial and temporal variability of measured or predicted rainfall on impacts even at a street scale. Specifically, the main goal of this research is to make a step to move toward the implementation of an effective flash flood nowcasting system in which timely and accurate impact warnings are provided by including weather radar products in the HPC 2D‐SWEs modelling framework able to integrate watershed hydrology, flow hydrodynamics, and river urban flooding in just one model. The timing, location, and intensity of the street‐level evolution of some key elements at risk (people, vehicles, and infrastructures) are also discussed considering both calibration issues and the role played by the spatial and temporal rainfall resolution. All these issues are analyzed and discussed having as a starting point the flood event which hit the Mandra town (Athens, Greece) on the 15 November 2017, highlighting the feasibility and the accuracy of the overall approach and providing new insights for the research in this field.