Assessment of future fluvial floods damages on buildings based on different climate scenarios: a case study in France

Today, there is no doubt climate change leads to more frequent and severe climate extremes in the future. Like other extreme climate events, fluvial flooding, which is already the most damaging climate extreme in France, will be more frequent, endangering the entire economy and financial system. As essential economic actors, financial institutions must be prepared to face higher resulting economic impacts caused by extreme fluvial floods, even in the close future. However, it is still difficult to analyze and quantify this physical risk and its resulting direct losses, particularly in the building sector. In this context, the necessity to integrate flood-related risks into financial risks (credit, market, and liquidity risks) can be done through the quantification of predicted climate-related damages.

In this study, we emphasize the results of the application of a new framework to calculate the direct damages from fluvial flooding on residential buildings and its future worsening due to climate change. The originality of our work is to develop a frequency analysis of the prediction of flood damages at the building scale by combining specific depth-damage functions (Grelot and Richert, 2019) and fine-resolution hazard maps for river flooding.

We calculate damages on buildings located in the center of Paris (close to Seine river) for different fluvial flood frequencies. The damage modeling is performed using national depth-damage functions that give relationships between flood depth, flood duration, and subsequent damage. The latter concerns the cost of repair or replacement of each elementary component of the buildings that will be damaged or destroyed depending on the flooding scenario. We consider three different types of buildings collective buildings, multi-storey individuals, and single-storey individuals. The water depths due to flooding defines exposed areas of buildings and are based on data extracted from maps provided by the Joint Research Centre (Alfieri et al., 2015). Those maps depict flood-prone areas for river flood events for six different flood frequencies (from 1-in-10-years to 1-in-500-years) and are based on the high-emissions “RCP8.5” global warming scenario.

For each return period, we detect the impacted buildings by crossing the building map created from the French National Building Database with the corresponding fluvial flood map. Total damages are then computed as the sum of damages predicted for each building type associated with the closest water depth value.

By using the expected annual damage (EAD) methodology, we have investigated the effects of climate change caused by decreasing the return period (increasing the frequency of events). The results show that an increase in the frequency of occurrence of flooding due to climate change (decreasing the return period) led to increasing in the value of annual damage.

REFERENCES :

Alfieri, L., Feyen, L., Dottori, F. and Bianchi, A., 2015. Ensemble flood risk assessment in Europe under high end climate scenarios. Global Environmental Change, 35, pp.199-212.

Grelot, F. and Richert, C., 2019. Floodam: Modelling Flood Damage functions of buildings. Manual for floodam v1. 0.0 (Doctoral dissertation, irstea).