Real-time forecasts of flood hazard and impact: some UK experiences Steven J. Cole

Testo completo

(1)E3S Web of Conferences 7, 18015 (2016) FLOODrisk 2016 - 3rd European Conference on Flood Risk Management. DOI: 10.1051/ e3sconf/2016 0718015. Real-time forecasts of flood hazard and impact: some UK experiences 1,a. 1. 1. Steven J. Cole , Robert J. Moore , Steven C. Wells and Paul S. Mattingley. 1. 1. Centre for Ecology & Hydrology, Wallingford, Oxfordshire, OX10 8BB, UK. 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.. 1 Introduction Major UK floods over the last decade have motivated significant technological and scientific advances in operational flood forecasting and warning. In part this has been driven by the UK Governme

(2) [1] of the summer 2007 floods which has increased focus on surface water flooding and distributed, national-scale hydrological modelling. Following the Pitt Review, new joint forecasting centres between the national hydrological and meteorological operating agencies have been formed: the Flood Forecasting Centre (FFC) over England & Wales and the Scottish Flood Forecasting Service (SFFS). Both joint centres issue a daily, national Flood Guidance Statement (FGS) to the emergency response community based on a Flood Risk Matrix approach that is a function of potential impact severity and likelihood [2, 3]. To support the FGS approach there is an increased demand for robust, accurate and timely forecast and alert information on fluvial and surface water flooding along with impact assessments at local, authority area and national scales. The Grid-to-Grid (G2G) distributed hydrological model has been employed by FFC [4] and SFFS [5] since 2010/11 to support 5-day ahead national fluvial flood forecasts using deterministic and ensemble rainfall products from the Met Office. As a first step, forecast fluvial flood severity (in terms of return period) has been used as a surrogate for impact. Recent research has explored linking the forecast fluvial flood severity to more detailed offline flood risk assessments that use an overall impact score combining human health, economic, a. cultural and environmental factors. This builds on a similar approach developed for surface water flooding (SWF) under the Natural Hazards Partnership (NHP) initiative, where impact assessments for detailed offline pluvial flood maps utilise national receptor datasets on population, infrastructure property and transport. Then dynamic gridded surface-runoff estimates from G2G can be equated to effective rainfall scenarios previously used as input to inundation models when creating the pluvial flood maps in order to select the appropriate impact assessment for each pixel and generate real-time maps of SWF impact. Firstly a brief introduction to the G2G Model and its national application for flood forecasting is given. Then the Flood Risk Matrix approach is introduced along with three case studies of forecasting flood impact. These concern: (i) an operational SWF trial by SFFS during the Glasgow 2014 Commonwealth Games, (ii) SWF developments for FFC over England & Wales under the NHP, and (iii) fluvial flooding over Scotland.. 2 The Grid-to-Grid (G2G) Hydrological Model

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(32) E3S Web of Conferences 7, 18015 (2016) FLOODrisk 2016 - 3rd European Conference on Flood Risk Management. DOI: 10.1051/ e3sconf/2016 0718015. frequently during an emerging flooding situation [2, 3]. Principal recipients of the FGS are the Category 1 and 2 emergency responders identified in the Civil Contingencies Act 2004 [6]. The FGS is based on a Flood Risk Matrix approach that combines potential impact severity and likelihood of occurrence as depicted in Figure 2. Several different types of impact are considered including people, property, transport and key infrastructure. These are also assessed at increasing severity levels of: Minimal, Minor, Significant and Severe. For example, localised flooding affecting individual properties is considered a Minor impact whilst widespread flooding affecting significant numbers of properties and whole communities is considered Severe. Full details are provided in the FFC and SFFS guides to the FGS [2, 3 assification of the Flood Risk Matrix (Figure 2) is defined using the following probability of occurrence bands: very low <20%, low 20-40%, medium 40-60%, high 60% or greater.. Figure 1. Schematic of the Grid-to-Grid Model..

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(116) %. 4 Operational SWF alert trial during the Glasgow 2014 Commonwealth Games The Scottish Environment Protection Agency (SEPA) has a commitment to develop appropriate forecasting and warning capabilities for Surface Water Flooding (SWF) in Scotland. In recent years there have been several notable floods resulting from intense rainfall in urban areas exceeding the capacity of local drainage systems. Glasgow has a history of surface water flooding with five notable events in the 12 year period 2002 to 2013. A flood in July/August 2002 was particularly severe with many houses and transport infrastructure affected. From 23 July to 3 August 2014, Glasgow was the host venue for the Commonwealth Games and this provided a unique opportunity and focus for developing and trialling a new Daily Surface Water Flood Forecast (DSWFF) service over a 10 by 10 km area of Glasgow. A collaborative project, funded by the Scottish Government, was commissioned through the Scottish Centre of Expertise for Waters (CREW, www.crew.ac.uk) with SEPA as the principal stakeholder. The research project brought together expertise from the James Hutton Institute, the Met Office. 3 The Flood Risk Matrix approach The FFC and SFFS both issue a national Flood Guidance Statement (FGS) on a daily basis and more. +

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(125) %. and Centre for Ecology & Hydrology. Operational implementation of the trial was managed by SEPA with additional system configuration support provided by Deltares. Full details are given in [10] whilst a summary follows.. 4.2 Methodology for impact assessments 5

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