Effects of spatial planning on future flood risks in urban environments

Urban development may increase the risk of future floods because of local changes in hydrological conditions and an increase in flood exposure that arises from an increasing population and expanding infrastructure within flood-prone zones. Existing urban land use change models generally consider the expansion process and do not consider the densification of existing urban areas. In this paper, we simulate 24 possible urbanization scenarios in Wallonia region (Belgium) until 2100. These scenarios are generated using an agent-based model that considers urban expansion and densification as well as development restrictions in flood-prone zones. The extents of inundation and water depths for each scenario are determined by the WOLF 2D hydraulic model for steady floods corresponding to return periods of 25, 50, and 100 years. Our results show that future flood damages and their spatial distributions vary remarkably from one urbanization scenario to another. A spatial planning policy oriented towards strict development control in flood-prone zones leads to a substantial mitigation of the increased flood damage. By contrast, a spatial planning policy exclusively oriented to infill development with no development restrictions in flood-prone zones would be the most detrimental in terms of exposure to flood risk. Our study enables the identification of the most sensitive locations for flood damage related to urban development, which can help in the design of more resilient spatial planning strategies and localize zones with high levels of flood risk for each scenario.