LULC scenarios; climate change impacts; semiarid

This research aimed to analyze the influence of future scenarios of climate and LULC (land use and land cover) in the watersheds of the Pajeú river and the Capibaribe river in relation to the flow regime and hydrological processes. For this purpose, the MGB-IPH hydrological model was used. The adopted future climate scenarios were the projections of the Eta/CPTEC regional climate model nested to global circulation models (scenario RCP 4.5). Future LULC scenarios were defined using the Land Change Modeler, based on the classifications of vegetation cover and land use developed by the Mapbiomas project. Thus, two LULC scenarios were developed for the Pajeú river basin, scenario 1 (transition from caatinga and pasture to agriculture) and scenario 2 (caatinga to pasture and agriculture). For the Capibaribe river basin, the future LULC scenarios were scenario 1 (transition from caatinga vegetation to pasture and agriculture) and scenario 2 (transition from caatinga and forest to agriculture). For both watersheds, the LULC map referring to the year 1985 was considered as a reference for comparing the results. The hydrological model was manually calibrated considering a single set of parameters for both watersheds, therefore, considering the HRU for the year 1985. The Nash-Sutcliffe coefficient ranged from 0.70 to 0.79 in the calibration and from 0.81 to 0.89 in the validation of the Pajeú river basin. In the model calibration of the Capibaribe river basin, the Nash-Sutcliffe ranged from 0.58 to 0.88 and the validation from 0.09 to 0.90. Then, the model was run for the period from 1961 to 1990 (baseline period) and for the period from 2041 to 2070 considering climatological data from future scenarios. The results showed that the parameterization of the model can influence the increase or reduction of the flow volumes and hydrological processes in relation to the LULC scenarios. There was a significant decrease in the peak flow (Q10) in the MGB-Eta-MIROC simulation for both basins. The MGB-Eta-BESM simulates a considerable increase in Q10 for both river basins, but with similar volumes. The MGB-Eta CanESM simulates a decrease in the peak flow for the two hydrographic basins, but with greater magnitude for Capibaribe. The MGB-Eta-HadGEM predicts an increase in Q10 and a significant decrease in Q90 for the Pajeú river and a decrease in Q10 and Q90 for the Capibaribe river. In relation to Q90, the MGB Eta-HadGEM simulated the highest flow volumes for the Pajeú. Finally, the magnitude of decrease or increase in flow projected by climate scenarios may be bigger or smaller depending on the associated LULC scenario.