Influence and interactions of input factors in urban flood inundation modeling: An examination with variance-based global sensitivity analysis

Flood risk assessment and management in urbanized area experience an increasing reliance on the supporting information provided by numerical flood modeling as a rapid and efficient tool. Although hydrodynamic modeling based on shallow water equations requires less parameters than hydrologic ones, uncertainties of the input factors describing both the driving forces and the complex urbanized environment still have important influences on the accuracy of the urban flood simulation results once induced into the modeling procedure. The influences of input factors of engineering concern in urban flood hydrodynamic modeling in an intensely urbanized area of 0.58 km(2) in the city of Chongqing, China with a mixture of different land-use types are investigated in this study by taking advantage of a variance-based global sensitivity analysis methodology with particular focus upon the interaction between the uncertainties of different input factors describing the external driving force, the underlying urban surface, the drainage loss and the spatial resolution of modeling. The global sensitivity analysis results are examined with regard to maximum values of the flood extent, water depth and discharge and their variation in the course of the urban flood propagation. Influences of the input factors and their interactions are observed to vary for different model outputs. From a spatially-distributed perspective, a dependence of the interactions between input factors is found to be upon the relative location of their acting area associated to the land-use type. Antagonistic effects of the input factors describing the underlying urban surface and the drainage loss for the rainfall-induced flood water accumulations and movements are analyzed with the flood evolution. Main effects of different input factors and their interactions are of a certain consistency with the underlying physical processes of the urban flood propagation from both static and temporal perspective of the global sensitivity analysis results.