Frequency Analysis of Rainfall Data Observed in 2011 and 2013 in Serrana Region, Rio de Janeiro State

Abstract The rain that fell in the Serrana region in January 2011 caused what was considered to be the worst disaster in the history of Brazil, with more than 900 deaths. On the other hand, the rain that fell in March 2013, which was a larger total, gave rise to 33 deaths. The present study sought to compare these two events, using hour-by-hour data from the warning system of the State Environmental Institute and the historical daily records of the National Water Agency. The daily data were converted using a specific disaggregation factor and were fitted to Gumbel’s probability distribution model. In Nova Friburgo, the recurrence interval for the 2011 event was 150 years. For Petrópolis and Teresópolis, the recurrence intervals for the 2013 event were 135 and 115 years, respectively. Despite recurrence intervals of the same order of magnitude, the disasters that were associated with these events had different effects in the municipalities studied. It is recommended that assessments on the criticality of a disaster should not be based solely on the precipitation, given that factors such as relief, soil moisture content, land occupation in areas at risk and previous occurrences of landslides may be determinants in the analysis.