Hydrologic　models　are　widely　used　for　projecting　influences　of　changing　climate　on　water　resources.　In　this　study,　we　compared　the　original　Soil　and　Water　Assessment　Tool　(SWAT)　model　and　an　enhanced　version　of　SWAT　model　with　physically　based　Freeze-Thaw　cycle　representation　(SWAT-FT)　for　simulating　future　annual　ET,　stream　flow,　water　yield,　surface　runoff,　and　subsurface　runoff　in　the　Upper　Mississippi　River　Basin　(UMRB).　SWAT-FT　projected　fewer　frozen　days　than　the　original　SWAT　model　due　to　its　better　representation　of　snow　cover　insulation　effects.　Both　models　derived　declining　trends　in　annual　streamflow　and　terrestrial　water　yield　in　the　late　21st　century　due　to　increased　ET　under　warmer　climate.　However,　these　two　models　exhibited　contrasting　mechanisms　underlying　the　streamflow　decline.　For　original　SWAT　model,　the　decrease　in　surface　runoff　was　the　major　driver,　while　for　SWAT-FT,　reduced　subsurface　runoff　was　the　main　cause.　In　general,　the　original　SWAT　model　predicted　more　surface　runoff　and　less　subsurface　runoff　than　SWAT-FT.　Further　geospatial　inspection　shows　large　discrepancies　between　these　two　models,　particularly　in　the　northern　colder　parts　of　the　UMRB,　where　the　maximum　differences　in　annual　surface　and　subsurface　runoff　reached　130　mm　yr(-1)　and　140　mm　yr(-1),　respectively.　Collectively,　the　results　demonstrate　the　importance　of　accounting　for　Freeze-Thaw　cycles　for　reliable　projection　of　future　water　resources.