Long-Term Evaluation of Satellite Precipitation Products for Extreme Rainfall and Water-Related Hazard Assessment Along a Mountainous Corridor in Northern Vietnam

Accurate rainfall information is essential for water-related hazard assessment in mountainous regions, where complex terrain and sparse gauge networks limit monitoring reliability. This study evaluated long-term rainfall characteristics and the performance of three satellite precipitation products—CHIRPS, GPM IMERG, and GSMaP—along the National Highway 6 corridor in northern Vietnam. Daily gauge observations from 11 meteorological stations with station-dependent records between 1961 and 2024 were used to characterize rainfall variability and heavy-rainfall frequency. Matched gauge–satellite records from 2001 to 2024 were evaluated using continuous statistical indicators, contingency-table metrics, empirical cumulative distribution functions, and percentile-based analysis. Data from 2025 were additionally examined as an extreme-rainfall case study, supplemented by visual gauge–satellite comparisons; however, these data were not used as an independent satellite-validation period. The long-term gauge records showed marked spatial variability in rainfall magnitude and threshold-exceedance frequency. In 2025, all 11 stations recorded daily rainfall exceeding 50 mm, while eight stations recorded events exceeding 100 mm. Satellite-product performance varied substantially among stations, rainfall thresholds, and evaluation metrics, and no product was uniformly superior. At the 100 mm/day threshold, the probability of detection ranged from 0.024 to 0.276, whereas the false alarm ratio ranged from 0.781 to 0.916. Upper-tail analysis showed contrasting product-specific behavior: at the 99th percentile, CHIRPS and GPM IMERG underestimated gauge rainfall by 20.95 and 8.95 mm, respectively, whereas GSMaP overestimated it by 35.57 mm. These findings demonstrate that local validation, uncertainty assessment, and application-specific adjustment are necessary before satellite precipitation products are used for flash-flood, rainfall-induced landslide, drainage-risk, and transportation-infrastructure assessments in mountainous regions.