The analyzed rainfall events
The rainfall during the analyzed period presented atypical seasonality for the area, with the autumn/winter (dry session) more rainy than usual (figure 4). The spring marked the start of the traditionally rainy session, but the summer, usually the wettest season, did not reach the usual rainfall levels, with less accumulated rain volume than the winter, which was the wettest season of this hydrological year.
The analyzed events presented distinct characteristics concerning the rainfall volume, the previous humidity conditions, and the intensity of precipitation (Table 1). Five of the eight events analyzed presented precipitation equal or greater than 30 mm accumulated during 24 hours, which characterizes intense precipitation as established by Dereczynski et al. (2009) for the city of Rio de Janeiro. The rainfall volumes presented better adjustment to the duration of events (r2 = 0.892; P < 0.001) than to the intensities (r2 = 0.209; P = 0.011).
The high rainfall volume observed during winter is more associated with the cold fronts strength than with a higher occurrence of these, with higher rainfall volumes at each occurrence compared to what usually occurs in other years. Thus, the autumn-winter session was characterized by a smaller number of rainy days compared to the spring-summer session, reflecting a trend towards a larger number of days of drought preceding the analyzed events that occurred in autumn and winter.