Climate change effects on hydrologic processes and water quality in the Connecticut River watershed.

Increased frequency and intensity of extreme weather events, driven by climate change, are expected to alter hydrological and water quality processes in the Connecticut River watershed. This study aims to model the temporal and spatial impacts of climate change on the watershed's hydrology and nutrient dynamics. We used the Hydrologic and Water Quality System (HAWQS), which incorporates the Soil and Water Assessment Tool (SWAT), to establish a baseline scenario and assess two climate scenarios: Coupled Model Intercomparison Project (CMIP5-) Representative Concentration Pathways (RCP) 4.5 and RCP 8.5. The model was validated using observed data from the United States Geological Survey (USGS) gage sites. Our results show that both climate scenarios will cause significant changes in hydrological processes, including a shift in precipitation seasonality, with more rainfall expected during winter and early spring. These changes will affect nutrient loading, shifting the seasonal peaks of nitrogen and phosphorus. Notably, the nitrogen-to-phosphorus ratio is projected to decrease across the entire watershed under both climate scenarios. These findings suggest that the altered hydrological regime and nutrient dynamics could have cascading effects on aquatic ecosystems, impacting phytoplankton and algal growth, with important implications for future nutrient management strategies.