This study estimates rainfall disaggregation coefficients for the State of Rio de Janeiro and for the Rio de Janeiro Metropolitan Region (RMRJ) based on automatic rain gauges from the CEMADEN network. A Python-based workflow collected time series, selected stations according to record length, extracted annual extreme events (10 min to 48 h), and calculated sub-daily to daily rainfall ratios for return periods of 2–100 years. The formulations proposed by Pfafstetter and Chen were evaluated through a case study to guide the model selection. In the RMRJ, 109 stations were analyzed and aggregated by municipality, resulting in the metropolitan mean disaggregation coefficient (COERM). The COERM values are close to those proposed by CETESB up to the 30 min–1 h duration range. However, the coefficients were up to 18.8% higher in the duration range between 1 h and 3 h relative to the 24 h rainfall, indicating a stronger temporal concentration of precipitation precisely in durations critical for urban drainage design.
Façanha et al. (Sat,) studied this question.
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