Daily rainfall disaggregation for Tocantins State, Brazil

Abstract

In order to design effective Brazilian hydraulic structures, it is necessary to obtain data relating to short-duration intense rainfall from historical series of daily rainfall. This recurring need can be fulfilled by rainfall disaggregation methodology. The objective of this study was to determine the intense rainfall disaggregation constants for the State of Tocantins and to compare these constants with those obtained for other regions of Brazil. For the modeling of the frequency of intense rainfall of different durations of less than 24 hours, the Gumbel probability distribution (GPD) was employed using rainfall series from 10 locations in Tocantins state. The results showed that the GPD was adequate by the Kolmogorov-Smirnov and Chi-square tests. The disaggregation constants presented low variability values for different return periods (from 10 to 100 years); the values for Tocantins state are: h_12h/h_24h=0.93, h_6h/h_24h=0.86, h_4h/h_24h=0.82, h_3h/h_24h=0.78, h_2h/h_24h=0.72, h_1h/h_24h=0.61, h_50min/h_1h=0.92, h_40min/h_1h=0.83, h_30min/h_1h=0.68, h_20min/h_30min=0.76 e h_10min/h_30min=0.46. The comparison of the results with those from studies developed for other Brazilian regions showed variations of up to -62.30%, allowing us to conclude that the use of local constants is important in the process of rainfall disaggregation.