Abstract
Changes in precipitation and air temperature may produce different impacts on the hydrological regime, compromising water supply. This study focuses on climate change impacts in the Verde River Basin (VRB), a tropical headwater basin in southeast Brazil, located in the state of Minas Gerais. The Variable Infiltration Capacity model (VIC) was calibrated and validated in the Verde River Basin. The downscaling (Eta Regional Climate Model, at 20-km resolution) of three Global Circulation Models (CanESM2, HadGEM2-ES and MIROC5) were used to drive the VIC for a historical baseline (1961-2005) and three time-slices (2011-2040, 2041-2070 and 2071-2099), under RCPs 4.5 and 8.5 scenarios. The scenarios were used as input in the hydrological model after bias correction. The hydrological model (VIC) showed satisfactory statistical performance in calibration and validation, with CNS varying from 0.77 to 0.85 for daily and monthly discharges; however, it overestimated some peak flows and underestimated the recession flows. Multi-model ensemble means predict increases of the minimum and maximum monthly average temperature for the investigated area at the end of the century. The Eta-CanESM2 indicated greater warming, mainly for RCP8.5 at the end the century, whereas Eta-HadGEM2-ES showed higher reduction in the precipitation for RCP4.5 at the beginning of the century and for RCP8.5 at the end the century, negatively impacting the evapotranspiration and discharge. Among the Regional Climate Models (RCMs), the Eta-MIROC5 showed minor changes in the components of the hydrological cycle. This study suggests that Global Circulation Models represent an additional uncertainty, which should be accounted for in the climate change impact assessment.
 Keywords: climate changes, RCP4.5, RCP8.5, VIC model.
Highlights
Changes in precipitation and air temperature associated with greenhouse gas emission increases have been studied through simulations accomplished by Global Climate Models (GCM)
The study of climate change on the regional scale depends on regional physical processes and geographical characteristics, the downscaling of the GCM simulations (Regional Climate Models, RCM) have been applied to assess regional hydrological variations caused by climate change (Rajib and Rahman, 2012; Chou et al, 2014b)
Viola et al (2015), using the Lavras Simulation of Hydrology (LASH) model forced by A1B scenario emission (4th Assessment Report, AR4), simulated the hydrological changes in four headwater basins of the Grande River, wherein the results showed a reduction in the annual discharge for the first time-slice (2011-2040) and a substantial increase after 2041
Summary
Changes in precipitation and air temperature associated with greenhouse gas emission increases have been studied through simulations accomplished by Global Climate Models (GCM). Some studies have investigated the impacts of climate change on the Grande River Basin headwater, indicating that both temperature and precipitation affect the discharge and total runoff magnitude (Viola et al, 2015; Alvarenga et al, 2016b; 2018; Oliveira et al, 2017). According to Nobre et al (2011), there is a considerable level of uncertainty regarding precipitation projections, there is significant convergence in the scenarios of a generalized increase in average air temperature and the frequency of heatwaves and hot nights (Marengo, 2007), impacting and consistently increasing water loss through evaporative processes and contributing to reduced water availability In this context, this research evaluated the hydrological impacts projected by two future scenarios (RCP4.5 and RCP8.5) using the downscaling of three GCMs (CanESM2, HadGEM2ES and MIROC5) by the Eta Regional Climate Model, in the Verde River Basin, southeast Brazil. The impacts of climate changes on smaller-scale can be helpful for management policies; i.e., the Rio Verde Basin (RVB) has its own Basin Committee, and it is responsible for administrating water uses
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