Urban flood risk is shaped by climate change and urban expansion. Here, we analyze CMIP6 projections and show that 26% of global urban areas are projected to experience contradictory precipitation trends, defined by decreasing totals yet increasing intensities. The hydrological implications of this pattern on cities are unclear. Thus, we combine high-resolution simulations of historical and future heavy precipitation events with a detailed urban runoff model. Using an ensemble of over 5,300 spatially shifted simulations, we find that future storms become more spatially confined while their short-duration intensities increase. Consequently, weak runoff peaks become weaker while strong peaks become stronger. This contrast is further amplified by urbanization. This pattern reflects more compact future storms that suppress runoff when missing the catchment yet amplify peaks when striking it, which amplifies over the neighborhood scale. This contrasting urban hydrological response to climate change poses a critical challenge for urban flood management.