Sensitivity Analysis of Peak Rate Factors for Floods Assessment in the Wadi Ibrahim Watershed

This study investigates flood behavior in the Wadi Ibrahim watershed by evaluating the sensitivity of flood estimates to different Peak Rate Factor (PRF) values, with a focus on their influence on peak discharge (Qp), time to peak (tp), volume (V) and inundation depth. Flood simulations were conducted using the Ari-Zo model, an empirical rainfall–runoff approach designed for arid regions, combined with unit hydrograph derivation across multiple PRF scenarios (Low, Medium, High, and NRCS) for 50-, 100-, and 200-year return periods. Envelope curves were constructed as validation to characterize the range of potential flooding. Comparative analysis indicates that the widely used NRCS model, including in Saudi Arabia, consistently underestimates Qp and overestimates tp relative to the Ari-Zo model. The Ari-Zo model produces sharper, faster-rising hydrographs with shorter durations, reflecting the rapid flash flood response characteristics of arid catchments. The Qp in the High scenario is up to 71% higher than in the NRCS scenario. Hydraulic modeling shows that the different water depths of the Ari-Zo model relative to the NRCS scenario are 0.8 m (Low-NRCS), 1.8 m (Medium-NRCS), and 3.3 m (High-NRCS) for the 50-year return period, with the High scenario inundating nearly the entire valley bottom. The study highlights that PRF selection and model choice significantly influence flood predictions, emphasizing the importance of using arid-zone-adapted models to ensure reliable flood risk assessment and resilient infrastructure planning.