Comparison of fluvial and pluvial flood risk curves in urban cities derived from a large ensemble climate simulation dataset: A case study in Nagoya, Japan

摘要

Flood disasters are caused by two types of flooding: pluvial and fluvial flooding. The different hydrodynamic characteristics of these two types have been intensively discussed in a literature. However, their impact and the resulting damage have not yet been examined in a comprehensive manner due to the lack of extreme rainfall data and/or computational costs of flood simulations. Recently, an increasing number of ensemble climate simulation data has become available, providing long-term rainfall data based on numerical climate simulations. This is a case study of a flooding in an urban area set in Nagoya City, Japan. We applied a large ensemble climate simulation database, d4PDF, to a pluvial and fluvial flood model and derived the flood risk curves for each type of flooding. The results indicated that pluvial flooding presents comparable economic risk to fluvial flooding (only 16% and 17% lesser damage at 50- and 100-year return periods, respectively) despite its significantly shallower flood depths (area with flood depth over 45 cm was only 10.5% and 5.4%, respectively). The significant impact of pluvial flooding is attributable to its wider flood area (despite shallower depths), impacting major economic assets sprawled over the city, including areas further away from the river. Furthermore, fluvial flood risk was managed by settling the Nagoya Castle (now the central economic district) on higher altitudes. The results suggest that pluvial flooding could have comparable economic risks to fluvial flooding in urban areas where major economic assets are not concentrated around streams as well as historical countermeasures are installed against fluvial flooding.