Abstract
This work evaluated dry and rainy conditions in the subregions of the São Francisco River Basin (BHSF) using the Standardized Precipitation Index (SPI) and Markov chains. Each subregion of the BHSF has specific physical and climatic characteristics. The data was obtained from the National Water Agency (ANA), collected by four pluviometric stations (representative of each subregion), covering 46 years of data, from 1970 to 2015. The SPI was calculated for the time scales of six and twelve months and transition probabilities were obtained using the Markov chain. Transition matrices showed that, at both scales, if the climate conditions were severe drought or rainy, switching to another class would be unlikely in the short term. Correlating this information with the probabilities of the stationary distribution, it was possible to find the regions that are most likely to be under rainy or dry weather in the future. The recurrence times calculated for the stations that belong to the semi-arid region were smaller when compared to the value of the return period of the representative station of Upper São Francisco that has higher levels of precipitation, confirming the predisposition of the semi-arid region to present greater chances of future periods of drought.
Highlights
Water is considered a renewable natural resource because it is constantly recovering through the processes of the hydrological cycle
Study area and data The study area is located in the São Francisco River Basin and the data was provided by the National Water Agency-Agência Nacional de Águas (ANA) through the National Information System on Water Resources (SNIRH, 2018)
The six-month scale is recommended for the observation of agricultural drought, while the twelve-month scale is better for hydrological drought assessment (WMO, 2012)
Summary
Water is considered a renewable natural resource because it is constantly recovering through the processes of the hydrological cycle. Due to its great potential for use, with demands for different uses, water grows increasingly more scarce. The São Francisco River Basin has experienced this shortage. The basin is very important to Brazil, for the volume of water transported in a semi-arid region, and for the potential uses of the water and for its historical and economic contributions to the region. The basin covers an area of about 634,000 km. The São Francisco River is approximately 2,700 km long and originates in the Serra da Canastra in Minas Gerais, flowing south-north through Bahia and Pernambuco, where it changes course until it reaches the Atlantic Ocean at the border between Alagoas and Sergipe (Brasil, 2018)
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