Daily rainfall disaggregation for Tocantins State, Brazil

Virgilio Lourenço Da Silva Neto,Marcelo Ribeiro Viola,Demetrius David Da Silva,Marcos Giongo,Carlos Rogério De Mello,Silvio Bueno Pereira

doi:10.4136/ambi-agua.2077

Virgilio Lourenço Da Silva Neto, Marcelo Ribeiro Viola + Show 4 more

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https://doi.org/10.4136/ambi-agua.2077

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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: h12h/h24h=0.93, h6h/h24h=0.86, h4h/h24h=0.82, h3h/h24h=0.78, h2h/h24h=0.72, h1h/h24h=0.61, h50min/h1h=0.92, h40min/h1h=0.83, h30min/h1h=0.68, h20min/h30min=0.76 e h10min/h30min=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.

Highlights

In the planning and management of soil and water resources, it is indispensable to have backgrounds related to the climatic variables, among which heavy rainfall may be highlighted (Souza et al, 2012)
According to Engida and Esteves (2011), Gyasi-Agyei (2005), Paola et al (2014) and Yusop et al (2014), an alternative to circumvent this data limitation is the application of the rainfall disaggregation methodology, which allows the estimation of short-duration heavy rainfall from the annual maximum daily rainfall monitored by standard rain gauges
Comparing this result to that of Manaus, we can observe the same value (0.19). This result agrees with Back's contention that the methodology of intense rainfall disaggregation has regional validity. These results show significant differences among the disaggregation coefficients of the northern region (Manaus and Tocantins), southern Brazil (Pelotas, coast and Santa Catarina’s outback) and mean coefficient values for entire the country

Summary

Introduction

In the planning and management of soil and water resources, it is indispensable to have backgrounds related to the climatic variables, among which heavy rainfall may be highlighted (Souza et al, 2012). According to Engida and Esteves (2011), Gyasi-Agyei (2005), Paola et al (2014) and Yusop et al (2014), an alternative to circumvent this data limitation is the application of the rainfall disaggregation methodology, which allows the estimation of short-duration heavy rainfall from the annual maximum daily rainfall (hday) monitored by standard rain gauges In this methodology, the 24-hour intense rainfall (h24h) is initially estimated from hday, as the difference between them relates to the fact that the latter corresponds to the depth observed based on a fixed interval of 24 hours, since the readings are performed daily at the same time (normally 0900 every day), while h24h relates to precipitation monitored during any 24-hour period by means of pluviographs, without fixing the beginning of the initial time (Mello et al, 2001). The pioneer study of CETESB (1980) is still used as a reference for heavy rainfall studies (Silveira, 2000; Mesquita et al, 2009; Garcia et al, 2011; Teodoro et al, 2014)

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