Large-scale floods can extend to several thousand square kilometres, with impacts at the regional and national level. At this scale in particular, interactions between hazard, exposure and vulnerability processes as well as dynamic developments of the flood risk system are important. These interactions must be considered if reliable risk estimates are to be obtained for developing effective and sustainable risk mitigation strategies. Yet, most flood research has centred on small- to mesoscale catchments and, to date, such requirements have usually been addressed by piecing together small-scale solutions. The EU-funded SYSTEM-RISK project addressed this challenge by developing a systems approach to large-scale flood risk assessment and management – from large river basins to the European scale. “We studied the complete flood risk chain from the meteorological processes to the adverse consequences, interactions and temporal changes in flood risk systems over large spatial scales,” says project coordinator Bruno Merz.
A large-scale approach
The initiative was a Marie Skłodowska-Curie European Training Network, instructing early-stage researchers in state-of-the-art methodologies to enable them to develop an integral view on flood risk systems. “Their research has focused on the understanding of the interplay between atmospheric and catchment processes, the interactions within the river-dyke-floodplain system, and the interactions of socioeconomic systems with physical processes,” Merz explains. The team implemented the systems approach in flood risk assessment and management, allowing upstream-downstream interactions within river systems to be considered. They included breaches to levees as well as the application of Big Data and the simulation of large-scale yet high-resolution flood scenarios, and unprecedented compound events. Researchers also developed the web application Smart-FLOOD, which enables the rapid mapping of flood-prone areas at high spatial resolution using hydro-geomorphic properties and the integration of Big Data. “It opens up new ways to explore flood risk systems and helps stakeholders in deriving strategies for risk reduction by enhancing their capability to efficiently process big data sets and produce high-resolution flood hazard maps over large scales,” comments Merz. The EU Floods Directive requires Member States to assess flood risks and provide risk management plans that do not significantly increase flood risks upstream or downstream of other countries in the same river basin or sub-basin. SYSTEM-RISK thus provided exactly the methods and tools needed to quantify such redistributions of flood risk and demonstrated that considering such spatial interactions leads to different decisions compared to the traditional, local approach.
Policymakers, flood risk managers and the insurance industry can all benefit from the work carried out by SYSTEM-RISK. By adopting a systems approach, they can gain a clearer picture of the underlying mechanisms of flood risk, and thus create improved management options for flood risk assessment and management. For example, upstream-downstream conflicts may arise from local flood protection measures. If during a flood the water level rises and causes flooding in one area, large amounts of water are stored in the hinterlands, lowering the likelihood of flooding downstream. Conversely, embanked rivers channel streamflow, move high water levels downstream and increase the likelihood of flooding downstream. This redistribution of flood risk only becomes visible when larger regions are considered. “SYSTEM-RISK therefore offers a framework for flood risk assessment, which considers effects of system behaviour,” Merz points out.
SYSTEM-RISK, systems, risk assessment, floods, river basin, Marie Skłodowska-Curie European Training Network, early-stage researchers