IMPACTO DAS MUDANÇAS CLIMÁTICAS NA VAZÃO E NA DINÂMICA DE SEDIMENTOS EM GRANDES BACIAS HIDROGRÁFICAS: ESTUDO DE CASO DA BACIA DO RIO DOCE

Abstract

Assessing the effects of climate change on flow and suspended sediments discharge provides relevant information for the development of water resources management plans and the elaboration of mitigation and adaptation strategies in river basins. This study verified the impacts of climate change on the flow and suspended sediments transport at the Doce river basin, located in the states of Espírito Santo and Minas Gerais. The basin has high sediment concentrations, which result in one of the highest sediment loads among large Brazilian basins. For this investigation, the MGB-SED and the future projections of the RCM Eta-BESM, Eta-CanESM2, Eta-MIROC5 and EtaHadGEM2-ES 20 km were used, with a spatial resolution of 20 km, and of the EtaHadGEM2-ES 05 km, with a spatial resolution of 05 km. Three future periods were considered for the simulations (2015 - 2040, 2041 - 2070 and 2071 - 2099), carried out with a daily time step, considering the climate scenarios RCP 4.5 and RCP 8.5. Simulations with the projections of climate models show a tendency to reduce the average annual flow and the average annual suspended sediments discharge in the Doce river basin in the 21st century. However, in some watercourses there may be an increase in the average annual flows and average annual suspended sediments discharges generated from the Eta-BESM and Eta-MIROC5 simulations, especially in the northernmost region of the study area. In the main tributaries and in the basin's outlet, the average annual flow trends vary from -5% to -84% in 2015 - 2040, from 0% to -76% in 2041 - 2070 and from -2% to -91% in 2071 - 2099. The average annual suspended sediments discharge trends at these points vary from -5% to -91% in 2015 - 2040, from +9% to -82% in 2041 - 2070 and from +12% to -93 % in 2071 - 2099. In the Suaçuí Grande river basin, positive variations were verified arising from the simulations with the projections of Eta-MIROC5. The results indicate considerable differences in the impacts of climate change on average annual flow and average annual solid discharge as a function of regional climate models and climate scenarios (RCP). However, the study carried out shows that all projections indicate that the Doce River basin may suffer serious problems related to decrease in flow, as well as significant reductions in the suspended sediments transport. Reductions in sediment transport in watercourses can significantly affect species habitats and channel erosion. Flow reductions, on the other hand, can compromise the supply of water for human consumption and the availability of water for agriculture, industry, electricity generation, which are important for eastern Minas Gerais and northwestern Espírito Santo.