Operationalising storage-discharge balance to enhance pluvial flood resilience: modelling and planning strategies in flat and sloping urban areas.

Storage and discharge are two fundamental solutions to strengthening pluvial flood resilience. Recent studies reveal that many urban catchments operate under a persistent storage-discharge imbalance, driven by urban densification. This 'imbalance' raises concerns in hydrologic, economic, spatial, and social aspects. This research aims to quantify the balanced relationship between storage capacity and discharge capacity (storage discharge balance, SDB) for pluvial flood protection and provide planning strategies for different urban topographies. We suggest and apply a quantification method using different modelling tools, hydrological and hydrodynamic models, in two cases with distinct physical and socioeconomic characteristics: one in a flat polder area in Nanjing, China, and the other in a sloping hilly area in Feldbach, Austria. By comparing these cases, insights are gained into the modelling methods, results, and proposed strategies for each context. The use of the SDB chart mapping framework supports the identification of both short- and long-term targets, as well as dynamic pathways toward enhanced flood resilience. These insights will facilitate multidisciplinary dialogue on key constraining factors, thereby enabling the co-creation of an actionable solution. While the quantitative findings are context-dependent, the novel approach can be applied to other cities to facilitate their resilience planning.