Extreme precipitation events in the state of São Paulo, Brazil: Spatiotemporal patterns and associated atmospheric mechanisms

ABSTRACT Extreme precipitation events (EPEs) are major drivers of natural disasters, often resulting in economic and social losses, infrastructure damage, and fatalities. In this context, advancing the understanding of their spatial behavior, frequency, and underlying atmospheric mechanisms is essential for improving preparedness and disaster risk reduction. This study examined EPEs across the state of São Paulo, the most populous region in Brazil, using daily rainfall data from 21 pluviometric stations for the period 1970–2022. Extreme events were defined using the 99th percentile (P99) threshold for each station. Results revealed a marked spatial contrast: the highest P99 values occurred in the northern and northwestern regions of the state, whereas the lowest thresholds were observed in the southern sector. On the other side, the frequency of days exceeding P99 showed the opposite pattern, with more EPEs recorded in southern São Paulo than in the north. Based on the days that exceeded P99, the atmospheric systems associated with EPEs were classified for the 1996–2022 period. Cold fronts accounted for 46% of the events, followed by the South Atlantic Convergence Zone (SACZ) at 28% and convective mesoscale systems at 26%. These findings highlight the distinct spatial and synoptic controls on extreme rainfall across São Paulo and underscore the need for region-specific monitoring and early warning strategies.