The Mississippi River basin is a very important source of water for civilian and agricultural usage. It is also very sensitive to climatological changes such as shifts in precipitation patterns that drive the streamflow of the Mississippi River basin. In this study, the MPI and GFDL GCMs were dynamically downscaled by Reg-CM4 under RCP 8.5 and bias correction as part of the NA-CORDEX program. Output from those simulations (Daily Precipitation, T min and T max) was then fed into the SWAT model to make hydrologic assessments for high water marks of the UMRB at Grafton, IL, in contemporary (1981-2010) and future scenario (2041-2070) climates. The growing seasons (May-Aug) of each period were also analyzed. Both MPI-RegCM4 and GFDL-RegCM4 produced similar projections for streamflow during the contemporary period. When the future projections were analyzed, GFDL-RegCM4 gave higher streamflow with greater exceedance of 2, 5, 10-year floods than MPI-RegCM4, especially during the growing season. The MPI-RegCM4 tended to simulate a dryer and hotter future scenario than GFDL-RegCM4 with greater potential evapotranspiration, less precipitation, and therefore lower evapotranspiration, water yield, and basin-wide snowmelt. Both models, however, projected greater inter-annual variability in the future scenario with higher standard deviations than their contemporary simulations. The importance of these implications is that this projected increase in inter-annual variability could drive streamflow to greater extremes on both ends of the spectrum.