Abstract—Floods are one of the most prevalent natural disasters in the world, posing substantial hazards to human life and causing extensive property damage. Reliable flood forecasting enables timelier flood rescue and evacuation, resulting in fewer socioeconomic losses. Despite improvements, existing flood forecasting systems lack the reliability required for practical use in real-world scenarios. Inaccurate forecasting can erode public trust, which may reduce the possibility that people will follow warnings in the future. This paper describes the application of the Radar Integrated Nowcasting System (RaINS) to produce 3h, 2h, and 1h calibrated Quantitative Precipitation Nowcast (QPN) data for input to flood forecasting. The radar QPN is used as alternative rainfall input to the hydrological model in HEC-HMS software to simulate an extreme flood event over the Langat River basin, Malaysia. RaINS data combine radar advection adopting SWIRLS (Shortrange Warning of Intense Rainstorms in Localized Systems) with the Numerical Weather Prediction (NWP) model. The results indicate that the radar Quantitative Precipitation Estimate (QPE) from RaINS can perform very well and is slightly better than the raingauge value in simulating the flood, with an NSE value of 0.77 for the raingauge estimation and 0.78 for the RaINS QPE. However, the QPN data have not performed as accurately as the QPE, especially for the 2h and 3h lead times. Nonetheless, although not quantitatively precise, the simulation results indicate that the QPN data can provide an early approximation of the impending flood disaster. Integrating QPN derived from the RaINS data with the HEC-HMS model can provide a flood nowcasting system with an extended lead time for timely warnings and rescue operations. The simulated case study is scalable to other regions. Further research is recommended to enhance the reliability of the QPN and the integrated flood nowcasting system.

Keywords—flood nowcasting, RaINS, Langat River Basin, mean bias correction, radar rainfall, Quantitative Precipitation Estimates (QPE), Quantitative Precipitation Nowcast (QPN)

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Cite: Wardah Tahir, Noor Shazwani Osman, Jazuri Abdullah, Muhammad Azizi Mohd Ariffin, Hafiz Hassan, Lariyah Mohd Sidek, Hidayah Basri, Suzana Ramli, Nursalleh K Chang, and Yip Weng Sang, "RaINS and HEC-HMS Applications for Flood Nowcasting in the Langat River Basin," International Journal of Environmental Science and Development vol. 16, no. 5, pp. 364-373, 2025.

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