Long‐Term Spatial–Temporal Variability, Trends and Extreme Rainfall Events Over Indonesia Based on 43 Years of CHIRPS Data

Understanding rainfall variability and trends across Indonesia is crucial for developing strategies to mitigate the impacts of climate change. This study examines the spatial–temporal variability and trends in rainfall across Indonesia using long‐term (1981–2023) Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS) v2.0 data. Rainfall variability was quantified using monthly and daily rainfall indices, while trends were examined with the Mann–Kendall test and the Theil–Sen method. Evaluation against 67 rain gauge stations showed high reliability of CHIRPS v2.0 data (CC > 0.7; RB < ±25%), supporting its use for long‐term analysis. The highest interannual variability, characterised by a coefficient of variation (CV) greater than 30%, is observed in southeastern Sulawesi, Maluku and southwestern Papua. In contrast, the interannual lowest variability (CV < 15%) occurs in Sumatra and Kalimantan, which also exhibit the lowest precipitation concentration index (PCI < 10) and precipitation concentration degree (PCD < 0.2). These patterns reflect strong influences of topography and geographic position on rainfall distribution. Trend analysis shows a general increase in annual rainfall across most of Indonesia, with significant rises (> 20 mm/year, p < 0.1) in central‐northern Sumatra, southeastern Sulawesi, Maluku and southwestern Papua, while northern Papua near the Pacific margin shows significant declines towards drier conditions. Monthly rainfall trends show strong positive changes in June and November and negative trends in September, reflecting heterogeneous monsoonal responses to climate variability. In addition to changes in total rainfall, significant upward trends are observed in the frequency and intensity of extreme rainfall events across parts of Sulawesi, Maluku and Papua, consistent with regions exhibiting the highest CV. The greatest increases in extreme rainfall frequency (R50mm), intensity (RX1day) and amount (R99p) are observed in Southern Sulawesi. The spatial disparities of rainfall trends and extremes across Indonesia emphasise the need for region‐specific adaptation strategies.