Estimativa de precipitação pluvial máxima para o estado de Mato Grosso do Sul

Abstract

The aim of this study was to establish and update the equations of intensity, duration and frequency for rainfall in Dourados and Campo Grande, in the State of Mato Grosso do Sul, based on a time series sufficiently long and representative of extreme events. To estimate the maximum rainfall in the region of Dourados two pluviographic measuring stations were used for data acquisition, one operated by Embrapa (CPAO) and the other by Federal University of Grande Dourados (UFGD), concerning the period from 1979 to 2010. For the region of Campo Grande, the data was obtained via a station operated by the National Institute of Meteorology (INMET). We determined the maximum annual precipitation with lengths of 10, 20, 30, 40, 50, 60, 120, 180, 240, 360, 720 and 1440 minutes and adjusted to the Gumbel probability distribution. The equations of intensity, duration and frequency of precipitation were adjusted using the non-linear adjustment technique Gauss Newton using Software SAEG 9.1. All series of annual maximum intensity were adjusted to fit the Gumbel distribution, according to the test Kolmogorov-Smirnov test. Subsequently, we calculated the values of intensity for the maximum annual rainfall for return periods of 2, 5, 10, 20, 50 and 100 years, which served as the basis for defining the rainfall equation for the regions studied. The results showed: the equation proposed (heavy rainfall to regions of Dourados-MS and Campo Grande-MS) can be used for the design of agricultural projects and hydraulic deployed in the region. Due to the lack of information concerning the equations of maximum precipitation for most locations in the State of Mato Grosso do Sul, as well as equations for accurate estimates, based on the period of time studied, the most viable alternative to perform hydraulic projects has is to use the information available from weather stations in close proximity with the locality in which the project is carried out, or make use of alternative methods, such as methods of disaggregation of rain in 24 hours, as well as Bell´s model, from rainfall data due to the greater availability of these stations and longer periods of observations. Based on this approach, we developed the second paper, in which we aimed to estimate the equations of maximum precipitation for the state of Mato Grosso do Sul through the adjustment of the alternative methods of disaggregation of rain in 24 hours and Bell´s model, based on the rainfall data obtained at the stations regarding of Dourados-MS and Campo Grande-MS, aiming to achieve an estimate of the average maximum intensity of rainfall, with relative precision, for locations that do not have pluviograph stations. For this, we used rainfall data from 105 stations available in the database of the National Water Agency. Based on the results we can conclude: the equations for heavy rains obtained through the analysis of rainfalls have good results, showing a coefficient of determination above 99%. The methodologies adjusted to obtain different lengths of rainfall from the height of precipitation at the site, lasting 24 hours and with a known return period, demonstrated satisfactory results when compared with the rainfalls analysis method (standard method): - the method of 24 hours precipitation disintegration proposed by DAEE/Cetesb (1980) tends to underestimate the maximum intensities of rainfall in the State of Mato Grosso do Sul; - the Bell method didn´t prove itself suitable for usage in the State of Mato Grosso do Sul, since it achieved the highest average relative error, in general, making it impractical for use in obtaining shorter rains to be employed in generating the relative intensity, duration and frequency; - the highest levels of rainfall expected in the State of Mato Grosso do Sul are in the west and lower in regions south and east.