Simulation of stream flow and hydrological response to land-cover changes in a tropical river basin

Abstract

Land cover of river basins has undergone multiple modifications and conversions as a result of various pressures on ecosystems. This study calibrates and validates the Soil and Water Assessment Tool (SWAT) model for determining the hydrological response to land-cover changes in the Lower-Middle São Francisco River sub-basin (LMSFR), Brazil. The SWAT model was calibrated with 1993–1994 data from hydrological station at Juazeiro, while data from the 1995–2004 period were used for validation. We analyzed three scenarios of land cover which were compared to current landscape (pasture land): scenario I (pasture land is replaced by natural vegetation), scenario II (pasture land is replaced by maize crop cultivation), and scenario III (pasture land is replaced by bare soil). Calibration of the SWAT model in the LMSFR produced good results, as all evaluation indices reached satisfactory values in both calibration and validation periods for Juazeiro and validation period at Floresta. However, the calibrated model, when applied to Abreus, did not accurately simulate monthly stream flow (where r2=0.51 and NE=0.26). Scenario III had the greatest impact and influence on the sediment yield, which corresponded to an increase of 93.7% in comparison to the current land cover. This study identified regions where reforestation should be urgently carried out in the north part and extreme south of the sub-basin due to the overall level of land degradation.