Empirical Rainfall Threshold Determination for Flooding in Sorsogon Province

Abstract

This study, titled “Empirical Rainfall Threshold Determination for Flooding in Sorsogon Province,” aimed to identify rainfall thresholds that could trigger flooding in the province. Sorsogon, located in the Bicol Region of the Philippines, is highly susceptible to flooding due to its topography, coastal location, and exposure to multiple weather systems such as tropical cyclones, shearlines, and monsoons. Using both descriptive and evaluative research designs, the study analyzed historical rainfall data from the PAGASA Synoptic Station in Juban, complemented by satellite rainfall estimates from the Global Satellite Mapping of Precipitation (GSMaP). Bias correction techniques were applied to improve the accuracy of satellite-derived rainfall data.
Results revealed that rainfall thresholds for flooding varied among municipalities: 70–80 mm for Magallanes and Juban, 80–90 mm for Sorsogon City and Irosin, and 90–100 mm for Castilla and Bulan. Tropical cyclones and shearlines were identified as the dominant weather systems causing flooding across the province.
Findings from this research support the integration of localized rainfall thresholds into flood early warning systems, enabling communities and disaster management offices to anticipate flood events more effectively. The results contribute to broader disaster risk reduction and climate resilience efforts aligned with Sustainable Development Goals 11 and 13.