Can Global Products Capture Precipitation Variability in the Galápagos Islands? An Assessment Based on Climatic Time-Series Components

Small islands such as the Galápagos Islands are highly vulnerable to changes in water availability, affecting ecosystems and communities. Understanding temporal precipitation variability is crucial but challenging due to limited ground-based observations. This study evaluates five global precipitation products (satellite, reanalysis and multi-source products) at a monthly scale, complementing conventional assessment against ground-based observations with the analysis of three climatic time-series components: seasonality, anomalies, and trends, which capture distinct aspects of long-term precipitation variability relevant to climate applications. The analysis focuses on Santa Cruz and San Cristóbal Islands, where long-term ground data are available, and includes a spatial comparison of global products across the entire archipelago. Results showed that reanalysis and multi-source products (ERA5-Land, MSWEP, MSWX) generally outperformed satellite-based products (CHIRPS, PERSIANN-CCS-CDR). For example, in the cool lowlands, reanalysis and multi-source products achieved correlation values between 0.81 and 0.94, bias ranging from −0.52% to −40.3%, and probability of detection between 0.76 and 0.96. These products showed high and medium agreement with ground data in precipitation seasonality, anomalies, and trend detection. In contrast, satellite-based products revealed lower correlation values between 0.52 and 0.86, a higher underestimation bias (−10.86% to −75.43%), a lower probability of detection (0.22–0.32), and only medium or no agreement with ground data in precipitation anomalies and trends, with no agreement in seasonality. All global precipitation products exhibited significant limitations in representing precipitation seasonality in the highlands. The component-based assessment complements conventional evaluation, offering deeper insight into how errors are distributed over time. This integrated approach supports a more informed selection of precipitation products for climate analysis and water resource management in data-scarce island regions like Galápagos.