Extreme rainfall events in a tropical complex-terrain environment: Identification and dynamical–thermodynamic evaluation in Petropolis, Rio de Janeiro (Brazil)

Extreme rainfall events pose major socioeconomic and environmental challenges, particularly in regions of complex topography such as Petropolis, in the Serra Fluminense of Rio de Janeiro State, Brazil. This study identified and characterized extreme daily rainfall events in the municipality over a 13-year period (2011–2023), based on hourly data from 18 rain gauge stations operated by the Rio de Janeiro State Environmental Institute (INEA), complemented by the MERGE precipitation product (mean Pearson correlation of 0.6) to fill gaps at stations with at least 70% data completeness. Extreme events were identified using the station-based 99th percentile of daily precipitation, calculated separately for each season, considering a 13:00–12:00 UTC accumulation period adjusted to the local timing of significant rainfall. The mean annual 99th-percentile threshold was 60 mm/day, ranging from 57 mm/day in winter to 97 mm/day in summer, with some southern stations exceeding 180 mm/day in a single day. The southern portion of the municipality consistently presented the highest annual rainfall totals and extreme thresholds. A total of 28 extreme events were identified during the study period, concentrated in summer and autumn. The event of 17 March 2013 was the most extreme, affecting 9 of the 18 stations with a mean accumulated rainfall above 300 mm and a median close to 290 mm. Its dynamical–thermodynamic analysis showed persistent low-level moisture supply, favorable upper-level circulation, and a mesoscale environment supportive of sustained convection. These results provide a quantitative characterization of extreme rainfall in Petropolis, relevant to hydrometeorological risk monitoring and management in mountainous regions.