Projected climate changes and land use/cover change (LUCC) have been identified as drivers of watershed nutrient and hydrological processes and are likely to happen jointly in the future decades. This research aimed to unveil how climate change and LUCC affect water, carbon and nutrient dynamics in the Missisquoi River watershed, Vermont. We used 12 scenarios of future climate data (2021 – 2050) generated by three GCMs under four Representative Concentration Pathways (RCPs). For LUCC, we used three different scenarios generated by Interactive Land Use Transition Agent-Based Model (ILUTABM). The three scenarios are Business As Usual (BAU), Prefer Forest (proForest) and Prefer Agriculture (proAg) in the period of 2021 – 2050. Combining each climate change and LUCC scenario resulted in 36 scenarios that were used to drive Regional Hydro-Ecologic Simulation System (RHESSys) ecohydrological model.

For streamflow, climate change scenarios had larger impacts than LUCC, different LUCCs under the same climate change scenario have similar annual flow pattern. Land use with more agricultural land had larger nitrogen loads. In contrast, climate change and LUCC have comparable impacts DOC loads. For phosphorus, we developed RHESSys-P by coupling DayCent phosphorus module with RHESSys to simulate Dissolved Phosphorus (DP) load. After calibration and validation of RHESSys-P, it was used to simulate DP load for 2021 – 2050 under all scenarios. Results indicated BAU and proForest annual loads were around 4.0 × 104 kg under all climate change scenarios; proAg annual loads increased from around 4.0 × 104 kg in 2021 to 1.6 × 105 kg in 2050 under all climate change scenarios. The results showed LUCC is the dominant factor for dissolved phosphorus loading.