Spatial Variations of Precipitation Anomalies in the Water Resources Management Units of the Aguapeí and Peixe Rivers (State of São Paulo, Brazil)

This study analyzed the spatial and temporal variability of precipitation in the western region of São Paulo state, specifically in the Water Resource Management Units of the Aguapeí and Peixe Rivers, using the Rainfall Anomaly Index (IAC) to identify patterns of rainfall heterogeneity at different scales. The mappings were carried out using the free QGIS software, employing the Inverse Distance Weighted (IDW) geospatial interpolation method to estimate precipitation values in areas not directly monitored by rain gauges. The analysis revealed a predominance of dry conditions ("Dry" class) in most of the region, interspersed with areas of above-average rainfall ("Humid" class). Extreme events of both drought and excessive precipitation were identified, particularly in recent decades, highlighting an intensification of climatic variability. The temporal analysis, based on historical series, indicated moderate seasonal trends, with more evident declines during the transition from summer to autumn and relative stability during the critical months of the rainy season. The results highlight the importance of continuous monitoring and the integration of geospatial tools in studying regional climatic dynamics. Moreover, they emphasize the need for adaptive strategies to mitigate the impacts of extreme climatic events on sensitive sectors such as agriculture, water resource management, and urban societies located in vulnerable areas.