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Land-use changes affect soil water balance. The Upper Grande River Basin (UGRB) headwaters have undergone intense modifications in land use. This study was conducted to simulate, using the LASH model, the impacts on the hydrological regime in the UGRB with five land-use trends: S₁ and S₂ – reforestation with eucalyptus covering 20 % and 50 %, respectively, from the current grassland area; S₃ – reforestation with eucalyptus covering 100 % of the current grassland area only in the sub-basins where this trend is predominant; S₄ and S₅ deforestation of 30 % and 70 % of the forest remnants in the Mantiqueira Range region for the cultivation of grasslands, respectively. Results demonstrate that runoff would be reduced due to the land-use changes by 51.65 mm yr⁻¹, 110.29 mm yr⁻¹ and 59.48 mm yr⁻¹ for scenarios S₁, S₂ and S₃, respectively. However, scenarios S₄ and S₅ could increase streamflow by 57.63 mm year⁻¹ and 156.78 mm year⁻¹, respectively. This indicates that land-use changes might make the basin more prone to flooding and other hazards associated with increased runoff.
