Índices de severidade de seca para a bacia hidrográfica do Rio Tocantins

Abstract

Drought is a natural phenomenon which occurs due to a prolonged moisturedeficit. Further, it often affects large areas and economic sectors, especially the water resources and the agricultural production. In this context, the aims of this study were to analyze the spatial and temporal distribution of the droughts’ occurrence and intensity, as well as their interaction with the meteorological and hydrological droughts, using both theStandardized Precipitation Index(SPI) and Standardized Streamflow Index (SSFI)for annual and quarterly scale in the Tocantins river basin (TRB). In addition, we verified the influence of macroscale climatic phenomena in this basin rainfall. We also analyzed the interference of potential evapotranspiration on the meteorological drought, usingself-calibrating Palmer Drought Severity Index (scPDSI). For this, we selected113 rain gauge stations located within and around the basin area and 9streamflow stations in the Tocantins river’s tributaries. With the rainfall and stream flow data organized, the SPI indexes were calculated and spatialized in the study area using ordinary kriging and SSFI. In order to analyze the macroscale climatic phenomena influence, the KNMI Climate Explorer (CE) platform was used to correlate the Niño phenomena (1 + 2, 3, 3.4, and 4), Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation (AMO) torain gauge station monthly historical series in theTRB. To analyze the influence of evapotranspiration on the meteorological drought, monthly scPDSI maps were acquired from the Climatic Research Unit(CRU) database for the dry years. We observed an incidence of the most severe droughts in the years of 1997-98, 2015-16 and 2016-17. On the other hand, the wet years were 1989-90, 1996-97 and 1999-00. It was possible to verify a strong influence of the meteorological on the hydrological drought, considering both annual and quarterly scales. The influence of Pacific and Atlantic Sea Surface Temperature (SST) on the occurrence of drought and wet events in the basin, mainly in the North region, was observed as well. In general, there is a concordance between the values of SPI and scPDSI, which shows a strong weight of the precipitation on the droughtoccurrences in TRB. However, in some cases, evapotranspiration interferedin the intensity of these events, especially during winter, with low rainfall values resulting in a greater weight of potential evapotranspiration in the final water budget.