Real-time modelling of surface water flooding hazard and impact at countrywide scales

In response to the floods of summer 2007, the subsequent Pitt Review and more recent events, the demand is growing for more robust, accurate and timely forecast and alert information on surface water flooding (SWF) along with impact assessments at local, area and national scales. A major impetus for recent progress has come through the Natural Hazards Partnership (NHP) which aims to deliver coordinated assessments, research and advice on natural hazards for governments and resilience communities across the UK. Under NHP, a real-time Hazard Impact Model (HIM) framework is under development that includes SWF as one of three hazards chosen for initial trialling. In contrast to rainfall-threshold based SWF methods, the NHP HIM prototype approach uses dynamic gridded surface-runoff estimates from the Grid-to-Grid (G2G) hydrological model. G2G is already employed for operational fluvial flood forecasting across England, Wales & Scotland and thus its use for SWF is a natural extension to consider. Novel methodologies for generating dynamic real-time maps and area-wide summaries of forecast SWF impacts have been developed that can employ rainfall forecasts in deterministic and ensemble form. Use is made of national receptor datasets of population, infrastructure, property and transport along with the recent Updated Flood Map for Surface Water (UFMfSW) over England & Wales. The prototype approach is outlined and illustrated through case studies, including some events from summer 2012. Finally, a perspective on future developments and possible operational implementation is given.