Abstract
Estimating the expected annual damage (EAD) due to flooding in an urban area is of great interest for urban water managers and other stakeholders. It is a strong indicator for a given area showing how vulnerable it is to flood risk and how much can be gained by implementing e.g., climate change adaptation measures. This study identifies and compares three different methods for estimating the EAD based on unit costs of flooding of urban assets. One of these methods was used in previous studies and calculates the EAD based on a few extreme events by assuming a log-linear relationship between cost of an event and the corresponding return period. This method is compared to methods that are either more complicated or require more calculations. The choice of method by which the EAD is calculated appears to be of minor importance. At all three case study areas it seems more important that there is a shift in the damage costs as a function of the return period. The shift occurs approximately at the 10 year return period and can perhaps be related to the design criteria for sewer systems. Further, it was tested if the EAD estimation could be simplified by assuming a single unit cost per flooded area. The results indicate that within each catchment this may be a feasible approach. However the unit costs varies substantially between different case study areas. Hence it is not feasible to develop unit costs that can be used to calculate EAD, most likely because the urban landscape is too heterogeneous.
Highlights
Recent extreme precipitation events in Denmark have created awareness amongst the general public about the challenges faced by urban societies in order to adapt to future climate conditions
Carrying out a larger number of simulations enables a better examination of the relationship between the damage cost and the return period
In this study three different methods were tested for calculating the Expected Annual Damage (EAD), all based on the log-linear relation between the damage cost and the return period
Summary
Recent extreme precipitation events in Denmark have created awareness amongst the general public about the challenges faced by urban societies in order to adapt to future climate conditions. Assessing adaptation measures based on their costs and benefits lag behind especially in large urban areas with a complex drainage network and urban context [5,6]. The rise of more detailed hydraulic models and more computational power has given urban water managers a better opportunity for describing the propagation of floods by combining 1D sewer models and 2D surface flow models [8,9]. These new tools allow for the possibility of flood damage costs to be estimated differently. With higher spatial resolution and a better description of flow processes it is possible to try and describe the very heterogeneous patterns seen in urban areas both with regard to the extent of flooding, and the distribution of assets
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