Flood damage functions based on a single physics- and data-based impact parameter that jointly accounts for water depth and velocity

Direct flood damage is commonly assessed using damage models (i.e., vulnerability functions and fragility curves), which describe the relationship between hazard, vulnerability, and the (probability of) damage for items exposed to floods. In this paper, we introduce a non-dimensional impact parameter that, according to the physics of damage mechanisms and/or tuned on field or lab data, combines water depth and flow velocity in a general and flexible form. We then suggest a general approach to assess relative damage functions for items of different nature, subject to either progressive or on–off damage processes. The proposed method enhances traditional tools that use inundation depth as the main (or only) explicative variable, and allows recasting the results from previous studies in an elegant, flexible and unique form. Compared to multivariate models that link flow variables to damage directly, the physics-based approach allows for an intelligible assessment of flood hazard and the associated damage, even in case of scarce or sparse data. The proposed impact parameter and the related procedure to assess the relative damage functions are applied to different kinds of exposed items (people, vehicles, and buildings), demonstrating the general applicability and validity of the proposed method.