How to cite: LIMA rPC, SILVA DD, PereIrA SB, MOreIrA MC, PASSOS JBMC, COeLHO CD AND eLeSBON AAA. 2019. Development of an annual drought classification system based on drought severity indexes. An Acad Bras Cienc 91:e20180188. Abstract: In order to characterize the occurrence and intensity of droughts in the Doce river Basin, as well as to develop a system for its classification, four different drought indexes were evaluated: Percent of Normal Precipitation (PNP), Deciles Method (DM), rainfall

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... omaly Index (rAI) and Standardized Precipitation Index (SPI). The indices were calculated annually, based on precipitation data from 89 rainfall stations of the Brazilian National Water Agency (ANA). Nine analysis units (AUs) were determined in the basin and the Thiessen Polygons method was used to obtain the average precipitation in the respective drainage areas. The indices were calculated for each AU and then related to the drought intensity classes. An overall classification of the indices was proposed for the drought classification system for a 30-year base period, from 1985 to 2015. The most critical hydrological years of the Doce river Basin in relation to the drought were the latter being the most critical of the last 30 years. The results show that the annual drought classification system proved to be efficient in the identification of events, allowing to verify that the Doce River Basin presents a severe climatic drought condition, on average, every seven years.