Abstract: The implementation of a Flash Flood Forecasting system (FFFs) is considered the first and most cost-effective way to mitigate the social-economic impacts of flooding. The Flash Flood Guidance system (FFGs) is a wellestablished FFFs, developed in the U.S., but currently applied in multiple regions across the globe. The heart of the system is the derivation of the Flash Flood Guidance (FFG), defined as the rainfall threshold above which minor flooding is expected over a specified region. The FFG is a function of the threshold runoff, i.e. the maximum runoff which can be safely routed through the studied region, and the soil moisture conditions. In this research work, the derivation of the FFG values for predefined soil moisture conditions is performed, for the Mandra subbasin, located within the western part of Attica region in Greece. A methodology is applied for deriving the threshold runoff, and establishing the rainfall-runoff model based on the Unit Hydrograph theory and the Soil Conservation Service, Curve Number method to perform the needed FFG computations. The result is the generation of threshold rainfall maps, for a predetermined accumulation period and different soil moisture conditions, which highlight the flood prone areas, as well as, showcasing the impact of soil moisture conditions in flood generation.     «

Abstract: The implementation of a Flash Flood Forecasting system (FFFs) is considered the first and most cost-effective way to mitigate the social-economic impacts of flooding. The Flash Flood Guidance system (FFGs) is a wellestablished FFFs, developed in the U.S., but currently applied in multiple regions across the globe. The heart of the system is the derivation of the Flash Flood Guidance (FFG), defined as the rainfall threshold above which minor flooding is expected over a specified region...     »