Relative impacts of climate and landuse changes on future flood damage along River Meuse in Wallonia

Climate change is expected to increase flood hazard across most of Europe, both in terms of peak discharge intensity and frequency. Consequently, managing flood risk will remain an issue of primary importance for decades to come. Flood risk depends on territories’ flood hazard and vulnerability. Beside climate change, land use evolution is thus a key influencing factor on flood risk. The aim of this research is to quantify the relative influence of climate and land use changes on flood damage evolution during the 21st century. The study focuses on River Meuse in Wallonia for a 100-year flood. A scenario-based approach was used to model land use evolution. Nine urbanization scenarios for 2100 were developed: three of them assume a “current tend” land use evolution, characterized by urban sprawl, while six others assume a sustainable spatial planning, leading to an increase in density of residential areas as well as an increase in urban functions diversity. A study commissioned by the EU has estimated a 30 % increase in the 100-year discharge for River Meuse by the year 2100. Inundation modeling was conducted for the present day 100-year flood (HQ100) and for a discharge HQ100 + 30%, using the model Wolf 2D and a 5m grid resolution Digital Elevation Model (Ernst et al. 2009). Based on five different damage curves related to land use categories, the relative damage was deduced from the computed inundation maps. Finally, specific prices were associated to each land use category and allowed assessing absolute damages, which were subsequently aggregated to obtain a damage value for each of the 19 municipalities crossed by River Meuse. Results show that flood damage is estimated to increase by 540 to 630 % between 2009 and 2100, reaching 2.1 to 2.4 billion Euros in 2100. These increases mainly involve municipalities downstream of a point where the floodplain width becomes significantly larger. The city of Liège, which is protected against a 100-year flood in the present situation, would undergo about 450 million Euros damage for a 100-year flood in the 2100, i.e. in-between 21% and 25 % of the whole damage increase. The influence of climate is three to eight times higher than the effect of land use change according to the land use evolution scenarios considered. Nevertheless, these two factors have a comparable influence on seven municipalities. Consequently, although a careful spatial planning would not considerably reduce the overall flood damage at the level of theWalloon part of the Meuse Valley, more sustainable spatial planning could efficiently reduce future flood damage at the level of several most critical municipalities. Reference Ernst, J, Dewals, B, Detrembleur, S, Archambeau, P, Erpicum, S, & Pirotton, M. (2010). Micro-scale flood risk analysis based on detailed 2D hydraulic modelling and high resolution geographic data. Natural Hazards, 55(2), 181-209

Flood risk analysis in the Meuse river basin

peer reviewedThe goal of the study presented in the paper consists in understanding the vulnerability of economic systems to a modification of the hydrology due to climate change in the Meuse river basin. The latter extends over several regions in four different countries. A transnational approach is thus necessary to keep consistency throughout the international catchment. In this paper, we begin by illustrating how a strong collaboration between scientists and water authorities of the different parts of the basin has lead to a consistent approach for conducting flood risk analysis. Hazard modeling was conducted to get flood maps in the whole basin, considering various climate scenarios. In Wallonia, accurate hydraulic simulations were performed with the fully dynamic flow model WOLF2D entirely developed at the University of Liege (Erpicum et al., 2010). The outcomes of this inundation modeling constitute suitable inputs for the subsequent exposure analysis. The latter has been performed at a meso-scale using land use maps (CORINE) and geographic database (PLI), aggregated into a set of five damage categories. Recently developed damage functions, which are the key part of the vulnerability analysis, has been chosen in relation with the damage categories indentified in the exposure analysis. To determine the value of the assets, a monetary approach has been employed, with the purpose of assessing prices per square meter for each damage category. In this paper, the focus is set on comparing several approaches to calculate the specific price of the residential damage category in Wallonia, and to compare with an existing micro-scale approach (Ernst et al., 2010)