Revisiting Conventional IDF Curves Using Energy-Based 30-Minute Peak Rainfall Intensity for Urban Stormwater Design: Evidence from İstanbul

Urban drainage systems in rapidly growing cities such as Istanbul are increasingly stressed by short-duration, high-intensity storms that exceed the assumptions of conventional Intensity–Duration–Frequency (IDF) design curves. This study re-examines 1-minute rainfall records from 18 meteorological stations across Istanbul to test whether current design thresholds capture flood-triggering conditions. We extract the maximum 30-minute rainfall intensity (I₃₀) from the steepest segment of cumulative rainfall curves and express it in mm h⁻¹ for direct comparison with design standards. I₃₀ is integrated with rainfall kinetic energy through the Precipitation Intensity Flood Forecast (PIFF) framework to diagnose short-duration hydrologic stress and map intra-urban susceptibility. Results show that flood-generating storms frequently exceed 20- and 50-year design intensities and that high-risk zones cluster across northern and western districts. These findings indicate that I₃₀-based metrics better represent contemporary convective extremes and support incorporating sub-hour intensity indicators into climate-resilient urban drainage design and municipal planning guidelines in İstanbul.