Assessment of the effects of land use and cover changes and climatic variability on streamflow in a Brazilian savannah basin

The intensification of water resource usage, correlated with changes in land use and cover as well as climate variability, has led to significant alterations in the hydrological cycle, impacting water availability in basins. This study assesses hydrological trends in the section of the Janeiro River basin located in the Brazilian savannah (Cerrado biome), focusing on the influence of anthropogenic activities and climate variability between 1985 and 2017. Using precipitation, actual evapotranspiration, streamflow, land use and cover, and water use authorization data, we applied statistical tests (Mann–Kendall, Sen's slope, Pettitt, and RHO Spearman) to identify trends, abrupt changes, and correlations. The results show a decreasing trend in average and minimum flows, with reductions of 30 to 40%, respectively, compared to the historical series average, not attributable to significant changes in precipitation but rather to an expansion of agricultural areas and an intensification of water consumption for irrigation. There was a reduction from 76.5% to the sum of Natural and Forest Formation areas and an increase of 71.1% in Agricultural areas. The correlation between land use changes and streamflows suggests that the conversion of natural vegetation into agricultural lands is directly associated with the decline in water availability. This study highlights the need for sustainable planning and management of water resources, considering the seasonality of water availability and agricultural demands, to mitigate the negative impacts on the hydrological cycle and ensure water sustainability in the Brazilian savannah region.