Abstract
ABSTRACT Based on historical series, for each locality, equations can characterize the relationship between intensity, duration and frequency of rainfall occurrence. The objective of this study was to present two equations that can describe the occurrence of intense rainfall in Pelotas, RS state, over the period 1982-2015. The two equations were denominated conventional and hybrid, depending on the probabilistic model used. Following the conventional methodology, the parameters of Normal, Log-Normal, Gumbel and Gamma probability distributions were adjusted by the maximum likelihood method for return periods of 2, 5, 10, 20, 25, 50 and 100 years. The maximum intensity values for the hybrid equation were obtained using the empirical model of Weibull, considering return periods of 2, 5, 10, 20 and 25 years. On the other hand, the same theoretical distributions used in the conventional equation were applied to return periods of 50 and 100 years. The Kolmogorov-Smirnov test was used to select the best fitting distribution for the data. In order to verify the information acquired through the Weibull empirical model in comparison to the theoretical distributions, the t-test was applied to the angular coefficients. Significant differences were not verified between the values of maximum rainfall intensities obtained using the two methodologies, for the pre-established durations and return periods. Thus, considering the maximum rainfall intensities values (durations of 5-1440 min) and return periods of 2-100 years in the municipality of Pelotas, RS, Brazil, both the hybrid and the conventional intense rainfall equations can be used.
Highlights
The intensity-duration-frequency (IDF) relationship of rainfall occurrence can be represented by mathematical models generated from historical data series, such as rainfall records, relative to the place of interest (Silva et al, 2002; Souza et al, 2012).The conventional methodology for obtaining intensityduration-frequency relationships has been widely reported in the literature (Goulart et al, 1992; Garcia et al, 2011; Damé et al, 2016)
Some questions still need to be answered: (i) Why theoretical models of probability should be used to obtain values of maximum intensity for return periods shorter than the length of the sampled period? (ii) What is the influence of the objective function on the intensity-durationfrequency relationships coefficients obtained through the numerical optimization algorithm? (iii) Can someone prove that there are no significant differences between the values of historical maximum intensity and those obtained through the traditional methodology?
The data used in this study were obtained from the Agroclimatological Station maintained by the Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA) and the Universidade Federal de Pelotas (UFPEL), and comprise 34 years of pluviographic records (1982-2015)
Summary
The intensity-duration-frequency (IDF) relationship of rainfall occurrence can be represented by mathematical models generated from historical data series, such as rainfall records, relative to the place of interest (Silva et al, 2002; Souza et al, 2012).The conventional methodology for obtaining intensityduration-frequency relationships has been widely reported in the literature (Goulart et al, 1992; Garcia et al, 2011; Damé et al, 2016). Despite the apparent availability of intensity-durationfrequency relationships, it is important to note that the limits of the equations are mostly unknown: these limitations may interest in particular the type of series used, the annual or partial rainfall duration (Sansigolo, 2008), the extension and representativeness of the series, the duration and the return period. In this view, the present work aims at obtaining intensityduration-frequency relationships from available pluviographic records (1982-2015) for the locality of Pelotas, Rio Grande do Sul state, by considering both conventional and hybrid methodologies and using both empirical and theoretical probability models Some questions still need to be answered: (i) Why theoretical models of probability should be used to obtain values of maximum intensity for return periods shorter than the length of the sampled period? (ii) What is the influence of the objective function on the intensity-durationfrequency relationships coefficients obtained through the numerical optimization algorithm? (iii) Can someone prove that there are no significant differences between the values of historical maximum intensity and those obtained through the traditional methodology?
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