3.2 Relative contributions of driving forces to urban flooding
Based on the two fitted BRT models (one for considering the driving forces without buildings, and another for considering all driving forces), the relative contributions of the explanatory factors to the urban flooding across the study area are presented in Fig. 4. The results indicate that landscape shape index, slope, green space ratio, and waterbody ratio play dominant roles in influencing the density of flooding hotspots, with total relative contributions reach at 82.36% in model without considering the buildings. Specifically, the relative contributions of landscape shape index, slope, green space ratio, and waterbody ratio are 38.19%, 25.5%, 11.13%, and 7.54%, respectively. The results are robust in model with considering all driving forces. However, we found that building metrics play a certain role, with total contributions is 21.03%. Among these building metrics, the relative contributions of the building congestion degree, building density, 3D shape index, and building coverage ratio exceed 3.76%. For the category levels, land cover configuration has the largest relative contribution (33.69%), whereas the drainage capacity has the least importance (3.87%). The importance of the topography, land cover composition, and 3D building morphology are nearly equal.