A precipitação pluviométrica em Pelotas/RS: tendência, sistemas sinóticos associados e influência da ODP (The rainfall in Pelotas/RS: trend, associated synoptic systems and PDO influence)

O estudo das alteracoes climaticas e de eventos extremos torna-se importante devido ao impacto que estes podem ocasionar. A partir da serie de precipitacao diaria (1982 a 2015) de Pelotas/RS/Brasil, objetivou-se neste trabalho: (i) detectar as possiveis tendencias na precipitacao; (ii) relacionar os eventos extremos de precipitacao aos sistemas meteorologicos que os ocasionaram; e (iii) analisar a influencia da Oscilacao Decadal do Pacifico (ODP) na variabilidade interanual. Para a analise de tendencia, foi aplicada as series total anual e trimestral o teste da regressao linear e de Mann-Kendall. Para analise dos eventos extremos foram selecionados os eventos de maior taxa de precipitacao relacionando-os aos sistemas meteorologicos que os influenciaram mediante a analise dos campos de pressao ao nivel medio do mar obtidos de dados de reanalise. A relacao entre os valores anuais de ODP e os totais anuais de precipitacao foi analisada de acordo com o coeficiente de Pearson. Os resultados mostraram que os dados analisados de precipitacao total anual nao possuem tendencia significativa, porem, quando realizado os testes por trimestre, somente as precipitacoes do 3o trimestre apresentaram tendencia nao significativa. Selecionou-se 18 eventos extremos ocorridos no periodo analisado, e desses, 12 apresentaram um padrao bem definido de centro de baixa pressao continental terminando como ciclone extratropical na costa do RS, e 9 ocorreram em anos de influencia do El Nino. Alem disso, os resultados obtidos indicaram uma relacao significativa entre o indice ODP e a variabilidade da precipitacao no municipio de Pelotas. A B S T R A C T: The study of climate change and extreme events is important due to the impacts related to them. Analyzing the daily precipitation series (1982 to 2015) of Pelotas/RS/Brazil, this work aims to: (i) detect possible trends in precipitation; (ii) relate the precipitation’s extreme events to meteorological systems that caused them; and (iii) analyze the influence of Pacific Decadal Oscillation (PDO) on interannual precipitation variability. For trend analysis, the linear and Mann-Kendall regression tests were applied to the total annual and quarterly precipitation series. For the analysis of extreme events, it was selected the events with highest precipitation rate, relating them to associated meteorological systems by analyzing the mean sea level pressure fields obtained from reanalysis dataset. The relationship between the annual PDO values and the total annual precipitation was analyzed using Pearson’s coefficient. Results showed that the total annual precipitation do not have a significant trend, but when the tests were carried out by quarter, only the precipitations of the third quarter presented a non-significant trend. From the 18 selected extreme events occurred during the analyzed period, 12 presented a well defined pattern of continental low pressure center ending as extratropical cyclone on the coast of RS, and 9 occurred in years of influence of El Nino. In addition, the results obtained indicated a significant relationship between the PDO index and the rainfall variability in the Pelotas. Keywords: heavy rainfall, El Nino Southern Oscillation, climate change, sea surface temperature, precipitation variability.