<p>The aim of this research is to analyze rainfall on temporal and spatial scales and identify trends in the Cananéia-Iguape Coastal System (CICS), located on the southern coast of the state of São Paulo. The current deficit in comprehending precipitation patterns and anomalies, particularly their influence on vulnerable coastal ecosystems such as mangroves amidst ongoing climate change, impedes effective territorial planning and natural resource management. This underscores the imperative for systematic investigations into localized rainfall regime alterations. For this purpose, rainfall data provided by CHIRPS were used. Monthly average data were extracted and organized into monthly, seasonal and annual averages. Trend analysis was performed for both temporal and spatial data, using RStudio for temporal analysis and Google Earth Engine for spatial analysis. The lowest rainfall values occur in winter (July, August and September), while the highest values are recorded in summer (January, February and March). Spatially, the largest rainfall volumes are concentrated in the southern sector of the study area, while the lowest values occur in the northern sector, a pattern that is maintained at all scales of analysis. With regard to the trend, annual rainfall shows a significant reduction of -8.123 mm/year. In the seasonal data, spatial analysis indicated a significant trend of reduced rainfall, especially in the JFM, AMJ and JAS periods. The reduction in rainfall is more evident in the northeast and southwest sectors of the study area. On a monthly scale, April stands out, as it shows a significant trend of reduced rainfall in the time series (-1.35 mm/year). On the other hand, in the spatial analysis, the month of October stands out for presenting a tendency for increased rainfall, varying between 0.1 mm and 7.0 mm/year, with a greater incidence in the central sector of the CICS. Reduced rainfall, especially during the less rainy period, can impact economic activities and mangroves, since rain is an essential element for their development. Although this study provides valuable results, it emphasizes the need for further research on extreme precipitation events and the influence of the Atlantic Oscillations and ENSO on regional precipitation variability.</p> Graphical Abstract <p> This graphical abstract provides a clear and visually structured summary of the study “Long-Term Rainfall Trends in the Cananéia-Iguape Coastal System, Brazil, Derived from CHIRPS Satellite Data (1981–2022)”. Designed to communicate both methodology and results in an accessible format, the figure uses intuitive visual elements to connect scientific content and visual clarity. The objective of the study is highlighted at the top of the graphic. In the Methodology panel, data acquisition and workflow are illustrated through a series of labeled icons. Rain clouds indicate the collection of daily precipitation data; a calculator symbolizes the calculation of monthly, seasonal, and annual averages; a trend line and slope represent the application of the Mann-Kendall and Sen Slope tests; and a map icon connects the analysis to the study area. This methodological sequence is compact yet comprehensive, guiding the reader from the raw data to the spatial modeling. The Results section is divided into two subpanels. The Temporal Scale highlights seasonal patterns, showing that the lowest precipitation occurs in winter (July to September), while the highest is observed in summer (January to March). A descending bar chart visually reinforces the main finding of the study, which is a statistically significant annual reduction in precipitation of -8.1 mm/year, making the trend visually interpretable. The Spatial Scale uses the simplified cutout of the CICS study area to indicate regional differences in precipitation distribution. The southern sector is marked by the highest precipitation, the northern sector by the lowest precipitation, and the northeast and southwest sectors show more evident reductions for the studied period. Directional arrows guide the reader’s interpretation of these spatial changes. Finally, the Conclusion emphasizes the general trend of decreasing precipitation in the CICS and highlights the need for more research, with a special focus on extreme events. </p>