Planning green infrastructure to mitigate urban surface water flooding risk - A methodology to identify priority areas applied in the city of Ghent

Urban surface water floods pose growing threats in urban areas, which cause not only massive physical water disturbance, but also loss of human lives, destruction of social and economic infrastructures and disorder of society. The number and scale of flood damage in urban areas will continue to increase in the next several decades due to global trend in urbanization and climate change. Despite the extensive construction of grey infrastructures, many cities in the world remain vulnerable to surface water flooding, especially during the extremely weather events. Since the 1990s, green infrastructure has developed as an alternative and sustainable approach to mitigate flood hazard in urban areas. Despite the great effectiveness of urban green infrastructures in alleviating storm water runoff, there is comparatively little research for planners and designers to determine an appropriate strategy for green infrastructure planning. To address this gap, we propose a GIS-based multi-criteria evaluation method to identify the priority areas to site green infrastructure, based on five criteria: 1) storm-water runoff mitigation; 2) social flood vulnerable group protection; 3) flood sensitive area road infrastructures protection; 4) flood sensitive area buildings protection and 5) environmental justice. The weights of the five criteria are defined by the Analytic Hierarchy Process. We focus particularly on mitigating urban surface water flooding risk and demonstrate how the method can be applied using a case study of Ghent.