Análise espaço-temporal da chuva e grau de secura via dados observacionais e produtos orbitais para a bacia hidrográfica do médio São Francisco

Abstract

Difficulties faced by irregular rainfall distribution and drought-related problems have affected northeastern semi-arid populations and surrounding regions. Therefore, the objective of this study is to analyze the rainfall and the degree of dryness in the Middle São Francisco Watershed (BMSF), through observational data and orbital products. Daily rainfall data from 22 stations located in the BMSF and adjacent areas from 2001 to 2017. After the acquisition, the consistency of the series was verified and they were reorganized. Then, cluster analysis was applied and homogeneous rain groups were identified in the BMSF via Ward, three groups: the first (G1) located in the eastern and southern part of the basin, the second (G2) located in the southeast, center and northwest of BMSF and the last (G3) integrates stations inserted in the northeastern semiarid. The beginning (September) and end (March) of the rainy season was determined by the methodology of Liebmann et al. (2007). Data from the MODIS sensor, the product MOD13A3 (Normalized Difference Vegetation Index - NDVI monthly with 1000 m resolution) for the years 2001 and 2017. NDVI was used to calculate the Vegetation Condition Index (VCI) and to measure the degree of local dryness. The driest areas of the BMSF, according to the VCI, are inserted in the semiarid and surrounding areas, while the regions with the lowest degree of dryness were found in the central part of this basin, similar to the rainfall regime. This relationship was confirmed only in the dry season with r> 0.7 and R2> 0.5, in the rainy season this ratio was low, for both r (0.4) and R2 (0.2).