Avaliação da ocorrência de seca no estado do Rio Grande do Sul

Abstract

Due to the occurrence of drought events, the state of Rio Grande do Sul has accumulated losses in the agricultural and economic production. Despite the technological advances, agriculture still depends on climatic and weather conditions and, therefore, studies should be conducted in order to help the investigation of drought behavior in various regions. An important step in the understanding of drought events is the use of indexes, which survey the situation, according to an intensity scale, which aims to give an overview of the water behavior in the region. Thus, this study aims to identify and characterize drought behavior by using meteorological indexes, at different time scales for 40 seasons, consisting of a series of rainfall data from 1913 to 2002, located in the state of Rio Grande do Sul, obtained from the database of the National Institute of Meteorology (INMET) and the National Water Agency (ANA). Therefore, two drought indexes were used: Standardized Precipitation Index, in the time scales of 1, 3, 6, 9, 12 and 24 months, in severe and extreme intensities, and the Moreno Index, a quarterly and half-yearly scale, in intense to severe intensities, as well as the count of the total number and sequence analysis of dry days. For data filling of daily precipitation series, the stochastic model was used applying the Markov chain from two states. The results indicated that for the Moreno Index, the quarterly level, compared to the half-yearly scale, showed a higher concentration of drought events. For the Standardized Precipitation Index, the main sequences of dry months were found in extreme intensity; the higher incidence of severe drought events coincided in 85% with periods of La Niña and the higher incidence of severe and intense drought events occurred from 1943 to 1952. As for the spatial distribution of the Standardized Precipitation Index, in the scales 6, 12 and 24 months, it adequately represented the results obtained in the sequences of dry periods.