RESUMO ABSTRACT: NUMBER OF RAINFALL DAyS FORECASTING FOR THE SOUTHERN HALF OF RIO GRANDE DO SUL USING THE SEA SURFACE TEMPERATURE (SST)This study presents a climate forecasting model of the Number of Rainfall Days (NRD) for some meteorological stations in Rio Grande do Sul using the Sea Surface Temperatures (SST) as the predictable variables. Two sets of data were used in this research: the monthly data of NRD, which were obtained from 5 meteorological stations located in the southern half of Rio Grande do Sul, in the period of 1982 until 2005; and the SST data, measured in the same period. This series was divided in two periods: the dependent period is from 1982 to 2002, and it was used to determine the predictable equations and the regression coefficients; and the independent period, which is from 2003 to 2005, and was used to validate the model. The SST data were employed to establish the relations between the variables through the regression analysis. Good results were obtained in the prediction of the NRD for the regions and all the months analyzed. The predictable and observed data had a very similar distribution of the variables. Although there was some predictable values that differed from the observed ones, but these differences were not significant. The higher differences between the foreseen and the observed values occurred in the independent period.

ABSTRACT. Climatic were found in November. In general, it was observed that the significant coefficients in the simultaneous correlations remained until lag 2, i.e., the SST in the Equatorial Pacific and South Pacific can be good predictors of the rain quality for the state of the RS, up to 2 months in advance.

On Rio Grande do Sul the seasons of the year are well defined being felt, in its peculiar characteristics, in the winter, in the spring, in the summer and in the autumn. The pluviometric regime is quite regular and the precipitations are well distributed during all the year on the State. The Multivariate Enso Index (MEI) lacks of a study about its relations with the precipitation. It is a numeric index that integrates the action of different factors that characterize the phenomenon and that oscilate between positive values for the warm phase, the El Niño, and negative values for the cold phase, the La Niña. It considers, in its composition, the following variables: sea level pressure, zonal and meridional wind components at the surface, the Sea Surface Temperature (SST), the air temperature at the surface and a cloudiness indicator. This work had the objective to study the relations between the MEI and the SST of the Niño regions with the precipitations on Rio Grande do Sul State. For this, it were utilized total monthly data of precipitation from 40 meteorological stations of Rio Grande do Sul, bimonthly data of MEI and SST of the Niño regions for the period 1950 to 2002. The correlation coefficients between the precipitation of the Rio Grande Do Sul with the MEI and the regions of the Niños showed low values due to the fact of if using only the months of the beginning and end of the event. The MEI, although to be a more complex index of the methodologic point of view, it does not improve the coefficients of correlation with the precipitation of the State of the Rio Grande do Sul, and it always presents lesser or equal values to obtained when using the TSM of the regions of the Niños in the out/nov and nov/dez coupled of months. The MEI and the Niños regions 3 and 3.4 present the highest correlation coefficient with the Rio Grande do Sul State precipitation for the bimonths oct/nov and nov/dec.

RESUMO-Uma das culturas de grande importância para a economia do Rio Grande do Sul é a videira. Embora as produções de vinho, suco de uva e demais derivados da uva e do vinho também ocorreram em outras regiões, a maior concentração encontra-se na região nordeste do Rio Grande do Sul. Um dos principais fatores que influenciam na qualidade potencial da uva é a precipitação. Para a videira, influem não somente a quantidade total de chuvas, mas também sua distribuição ao longo do ciclo vegetativo. Por esses motivos, é de fundamental importância o estudo da precipitação na região nordeste do Estado. Dentre as variáveis pesquisadas que relacionam a variabilidade da precipitação, destaca-se a Temperatura da Superfície do Mar (TSM). Os objetivos principais deste trabalho são: identificar os padrões de anomalias da TSM dos oceanos Atlântico e Pacífico e suas relações na precipitação, na região nordeste do Rio Grande do Sul, nos meses de outubro a março. Dessa forma, procurou-se investigar a possibilidade de uma previsibilidade da precipitação com alguns meses de antecedência e, conseqüentemente, uma possível previsão da qualidade potencial da uva para aquela região. Os resultados mostraram que o primeiro padrão principal de sete áreas oceânicas apresentou correlação altamente significativa com a precipitação acumulada de janeiro e fevereiro nesta região e, conseqüentemente, uma correlação com a qualidade potencial da uva. Também ficou evidente a alta previsibilidade do padrão predominante nos meses de janeiro e fevereiro, a partir de anomalias da TSM média de outubro-novembro. Termos para indexação: Variabilidade da precipitação, qualidade potencial da uva, anomalia de TSM.

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