Flood Forecasts for Urban Basin with Integrated Hydro‐Meteorological Model

We describe a system for forecasting flood risk in the 370 km2, largely urban Kifissos Basin, Athens, Greece, located in moderate to steep terrain (∼3 h hydrologic response time). A 42 h flood forecast lead time is achieved through the use of an integrated hydro-meteorological system. Rainfall is forecast, on a 6 km grid, with a chain of nested numerical weather prediction models, consisting of a limited area model initialized with results of a global circulation model. Flood risk is assessed by driving a hydrologic model with the forecasted rainfall. The system’s forecast skill is evaluated for two recent, medium-size storm events. Results are encouraging for this initial operational stage, however, they also indicate that integrated hydro-meterological models are not yet mature tools. The weaker part of flood risk assessment is the rainfall forecast, which underestimated cumulative depths and maximum intensities and overestimated duration.