Economic assessment of measures aimed at reducing flood damageto buildings using computer modelling and expert judgement

Abstract. To limit the losses due to floods, public authorities can try to foster the adoption of private measures aimed at reducing the vulnerability of the dwellings. However, the efficacy and cost-efficiency to reduce material losses of such measures are not well-known. In particular, a better understanding of the influence of buildings characteristics and flood parameters on these variables would help identify the measures that are relevant to implement in specific contexts. We examined this topic for three groups of measures taken on existing dwellings: one consists in elevating the dwelling, one in dry-proofing it, and one in using construction materials that are resistant to water or cheap to replace. We combined expert judgement and computer modelling to assess their cost, efficacy, and cost-efficiency for a wide range of flood depth and duration, building characteristics, and level of exposure. We found that the value of the building components has a positive effect on the efficacy of dry-proofing and elevating a dwelling. Both the efficacy and cost of these two groups of measures increase with the size of the dwelling. Moreover, according to our results, dry-proofing and elevating a dwelling are unlikely to be cost-efficient for dwellings that are not exposed to floods with a return period lower than 100 and 30 years, respectively. Our findings also highlight that it is often less expensive to use the adapted than the original materials when rebuilding a damaged dwelling. Moreover, adapting the materials of an intact dwelling is unlikely to be cost-efficient for dwellings that are not exposed to floods with a return period lower than 20 years.