Unlocking the potential of surface water flood nowcasting for emergency services in a changing climate

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Surface water flooding affects 3.2 million properties in England, and is seen as "the biggest flood risk of all" by the Environment Agency. Average annual damage due to surface water flooding in the UK exceeds £290 million. Climate change is expected to increase the intensity of heavy bursts of rainfall, and weather is expected to become more 'uncertain' and 'unfamiliar'. The cost of associated damage under climate change could rise by 40% by the 2050s if current management approaches remain unchanged. In the UK, Ambulance and Fire & Rescue Services are the primary emergency responders to extreme flood events, during which demands for services often peak. For example, London Fire & Rescue Service saw more than a three-fold increase in emergency 999 calls attended during flooding on the EU Referendum Day (23 June 2016). Surface water flooding such as this affects the operation of emergency responders who have to operate under flood conditions, while meeting their mandatory response time target. For example, the majority of Fire & Rescue Services in the UK aims to reach incidents within 8-10 minutes. Flood incidents compound the challenges of meeting their response time targets. For example, during the 23 June 2016 flooding, the average response time of London Fire Brigade increased from 6 minutes under normal days to 16 minutes, thereby missing the response time target. 40% of incidents were reported to be delayed due to weather, flooded roads, and congestion. To combat this and enable effective decision making, knowing where and when it could flood is important.The operational decision making of emergency responders often involve determining when and where to allocate resources (e.g. closing flooded roads; pumping road sections to allow access; dispatching sandbags; positioning emergency vehicles; arranging cross-boundary and multi-agency operations). However, current system for predicting surface water flooding is not designed for operational purpose. The only (based on our knowledge) system exists is the UK Flood Forecast Centre's daily service, which provides 5-day outlook of flood risks including surface water flooding. A flood guidance document is issued daily and surface water flood risk is provided at the county-level, based on a pre-fun library of impact scenarios, rather than real-time analysis of risks. The spatial resolution and temporal frequency of the existing system means that such detailed decisions cannot be supported. Fundamentally, episodes of surface water flooding are typically less than 2-3 hours in the UK and associated with convective weather systems. Daily forecasts of surface water flooding are not able to capture the spatiotemporal dynamics of the fast-developing convective storms associated with such events.Under two NERC projects (2016, 2018), we developed the first nowcasting technology for surface water flooding. This approach involves around the clock real-time modelling of surface water flooding at street-level resolution for the next 3-6 hours, updated every 2-3 hours. In this way we use the latest weather forecast from the Met Office and capture every short duration intense rainfall events that cause flooding. Our stakeholder-driven research and innovation in surface water flood nowcasting have opened up several new, untapped research and innovation opportunities. The proposed project aims to address two key research questions in order to unlock the potential of surface water flood nowcasting for emergency services to support their operational decision making in a changing climate. These include: (i) uncertainty propagation from precipitation nowcasting and forecasting products to high-resolution surface water flood predictions; and (ii) effective communication of complex surface water flood risk information to support emergency responders' operational decision making.