Spatiotemporal classification of flood-triggering rainfall in urban watersheds of Mamminasata, Indonesia

Urban flooding is increasingly recognized as a process influenced not only by extreme daily rainfall but also by interactions among rainfall temporal evolution, spatial distribution, antecedent watershed conditions, and urbanization under climate change. In the Mamminasata metropolitan region of Indonesia, drained by nine watersheds with contrasting geomorphology and urban development, identifying flood triggering rainfall patterns is essential for flood risk management. This study aimed to classify spatiotemporal rainfall patterns associated with flood events and to examine their relationship with hydrologic response in urban watersheds. An event-based framework was applied to 53 flood events using GPM IMERG satellite rainfall data and peak discharge simulations from a hydrologic model. Temporal rainfall patterns were classified based on the relative contribution of antecedent rainfall and event-day rainfall within a five-day antecedent, one-day trigger, and five-day post-event window, while spatial patterns were classified according to rainfall dominance across upstream, mid-watershed, and downstream zones. These dimensions were combined to construct a spatiotemporal typology of flood triggering rainfall. Results showed that most flood events were associated with combined antecedent and trigger rainfall and with spatially diffuse rainfall concentrated in downstream and mid watershed areas. Hydrologic response analysis indicated that high peak discharge could occur under moderate event-day rainfall, indicating that daily rainfall extremes alone are insufficient to explain the occurrence of documented floods. These findings emphasize the importance of spatiotemporal rainfall classification and provide an empirical basis for improving early warning systems, design rainfall representation, and flood mitigation planning in Mamminasata and similar multi watershed urban regions.