Search for a command to run...
Flood hazards in monsoon-dominated river basins are influenced not only by total rainfall but also by the temporal sequencing, duration, and structural characteristics of typhoon events, particularly when these interact with the southwest monsoon (Habagat), a dominant driver of seasonal precipitation in the Philippines. However, many local flood studies in the Philippines rely on single representative storms, limiting their ability to capture how varying rainfall patterns influence runoff generation and floodplain dynamics. This study addresses this gap by analyzing six typhoon events—two pure typhoons and four enhanced by the southwest monsoon—and assessing their effects on the hydrologic and hydraulic response of the Talisay River basin in Balanga City, an urban catchment frequently affected by riverine flooding. Specifically, Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) was used to simulate rainfall–runoff processes under varying storm structures, whereas two-dimensional floodplain dynamics were modeled in Hydrologic Engineering Center-River Analysis System (HEC-RAS) using high-resolution terrain, land cover, and soil datasets. The modeling framework enabled a consistent comparison of peak discharge behavior, water surface elevations, flood depths, and inundation extents across events. The results showed a clear divergence between pure typhoon events and monsoon-enhanced storms, with the latter consistently producing higher runoff volumes, prolonged hydrograph responses, and far more extensive flooding. Monsoon-enhanced storms generated markedly different hydrologic signatures, including multi-peak hydrographs, sustained runoff, and peak discharges 1.5 to 1.7 times higher than those of pure typhoon events. Hydraulic simulations revealed even stronger contrasts where river stages increased by 0.5 to 1.2 m, inundation areas expanded up to 2.8 times, and flood depths exceeded 3 m in several low-lying barangays. Among all events, Typhoon Butchoy–Carina, which was intensified by the southwest monsoon in 2024, produced the most severe impacts and amplified inundation across all 10 of the most affected communities. These findings demonstrate that rainfall pattern variability plays a critical role in shaping flood severity, surpassing the influence of rainfall intensity alone. Incorporating compound storm characteristics into local flood assessments is therefore essential for effective planning, infrastructure design, and community-level risk reduction in monsoon-exposed river basins.