The use of modeling as a support tool for crisis management and decision planning requires fast simulations in complex built-up areas. The Parallel Micro SWIFT SPRAY (PMSS) modeling system offers a tradeoff between accuracy and fast calculations, while retaining the capability to model buildings at high resolution in three dimensions. PMSS has been applied to actual areas of responsibilities of emergency teams during the EMERGENCIES (very high rEsolution eMERGEncy simulatioN for citIES) and EMED (Emergencies for the MEDiterranean sea) projects: these areas cover several thousands of square kilometers. Usage of metric meshes on such large areas requires domain decomposition parallel algorithms within PMSS. Sensitivity and performance of the domain decomposition has been evaluated both for the flow and dispersion models, using from 341 up to 8052 computing cores. Efficiency of the Parallel SWIFT (PSWIFT) flow model on the EMED domain remains above 50% for up to 4700 cores. Influence of domain decomposition on the Parallel SPRAY (PSPRAY) Lagrangian dispersion model is less straightforward to evaluate due to the complex load balancing process. Due to load balancing, better performance is achieved with the finest domain decomposition. PMSS is able to simulate accidental or malevolent airborne release at high resolution on very large areas, consistent with emergency team responsibility constrains, and with computation time compatible with operational use. This demonstrates that PMSS is an important asset for emergency response applications.
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