Real-time forecasts of flood hazard and impact: some UK experiences

Abstract

Abstract. Major UK floods over the last decade have motivated significant technological and scientific advances in operational flood forecasting and warning. New joint forecasting centres between the national hydrological and meteorological operating agencies have been formed that issue a daily, national Flood Guidance Statement (FGS) to the emergency response community. The FGS is based on a Flood Risk Matrix approach that is a function of potential impact severity and likelihood. It has driven an increased demand for robust, accurate and timely forecast and alert information on fluvial and surface water flooding along with impact assessments. The Grid-to-Grid (G2G) distributed hydrological model has been employed across Britain at a 1km resolution to support the FGS. Novel methods for linking dynamic gridded estimates of river flow and surface runoff with more detailed offline flood risk maps have been developed to obtain real-time probabilistic forecasts of potential impacts, leading to operational trials. Examples of the national-scale G2G application are provided along with case studies of forecast flood impact from (i) an operational Surface Water Flooding (SWF) trial during the Glasgow 2014 Commonwealth Games, (ii) SWF developments under the Natural Hazards Partnership over England & Wales, and (iii) fluvial applications in Scotland.

The challenge of forecasting impacts of flash floods: test of a simplified hydraulic approach and validation based on insurance claim data

“…A large number of simultaneous alarms may be generated in the case of a significant rainfall event by such highly distributed flash flood forecasting systems. And it is now recognised that end users, such as emergency managers, who have little time for situation analysis and decision making during flash floods, crucially need rapid assessment of the possible field consequences and damage severity (Schroeder et al, 2016;Cole et al, 2016). Moreover, a direct forecast of possible field consequences opens the possibility for assessing the performance of flash flood forecasting systems in ungauged areas, based on reported consequences, as a surrogate for measured flood discharges (Versini et al, 2010a;Naulin et al, 2013;Javelle et al, 2014;Moncoulon et al, 2014;Saint-Martin et al, 2016;Le Bihan et al, 2016).…”

Developing surface water flood forecasting capabilities in Scotland: an operational pilot for the 2014 Commonwealth Games in Glasgow

“…Although the surface runoff reporting thresholds were set at 13.5 mm and 16 mm in 3 h for low and high runoff (based on the thresholds used by Cole et al , ), in some individual cells, impacts were shown to start occurring when surface runoff reached 8 mm in 3 h. The risk maps were colour‐coded using the Flood Risk Matrix overall risk colours, enabling flood risk to be easily identified. A 5% reporting threshold was set so that the output grids would only be populated if two or more ensemble members exceeded the threshold.…”

“…Recently there has been a focus on explicitly coupling impact assessments with flood forecasts (Cole et al , ). A major modelling issue in relation to surface water flooding is gaining information on impacts and flood extent in order to validate the efficacy of a given modelling approach.…”

“…By bringing dependence on surface cover, soil properties, and antecedent wetness condition, G2G offers a potential advance on such approaches. Under the Natural Hazard Partnership (NHP, ), a case study has pointed to the potential value of G2G for surface water flooding alerts, and further development is ongoing (Cole et al , , ). Therefore, G2G was selected for use in this application.…”

“…Surface runoff for each 1‐km grid cell was simulated by the G2G Glasgow model. Similar to Cole et al (), it was assumed that the surface runoff from the G2G model was equivalent to the effective rainfall used to produce SEPA's regional pluvial flood maps. This meant that for each 1‐km grid square, the most appropriate flood inundation map and impact assessment from the offline library could be identified.…”