Dendroclimatology in seasonally dry tropical forests in the São Francisco Basin, Brazil

Abstract

This work aimed to develop dendroclimatic studies in seasonally dry tropical forests in the São Francisco River Basin, Brazil. Complete cross-sections and cores from Cedrela fissilis Vell trees were used to build two ring-width chronologies in the north of the state of Minas Gerais. The procedures for sample preparation, counting, co-dating and measurement of growth rings were made according to standard dendrochronological procedures. The produced chronologies, called Juvenília and Peruaçú, presented significant intercorrelation between the series (RBAR) equal to 0.52 and 0.34, respectively. In the Juvenília chronology, dated from 1961 to 2015, we verified the strong correlation between the tree growth and total precipitation of the wet season (October to March), that spatially covered the main tributary sub-basins of the São Francisco river, in some areas the correlation was higher than r = 0.60. The Peruaçú chronology, dating from 1842 to 2012, was used to reconstruct the average monthly flow of the São Francisco River at the Sobradinho observation station (Bahia state) between November and February, and explained 54% of the variance in the calibration period (1956-1998). Historical droughts that occurred in the basin were identified in the chronology, such as the "Grande Seca" that occurred between 1875-1879 and the 1932 drought, which caused great migratory waves in the "Brazilian Drought Polygon". The results show the great potential for dendrochronological studies in the São Francisco river basin, a region vulnerable to severe drought events. The information generated in this research contributes to the understanding of the water regime in the basin and provides information for planning the multiple use of water.