Modeling assessment of climate change impacts on water quality in Chesapeake Bay

Climate change has and will have impacts on coastal waters, and robust future projections are critical for adaptation and restoration planning in the Chesapeake Bay region. Within the framework of the Chesapeake Bay Program (CBP), a series of climate change scenarios have been simulated with airshed, watershed, and estuary models to examine the influence of environmental conditions on Chesapeake water quality by 2025 through 2065, with a 10-year interval of assessment, as compared to a base case of 1995. Down-scaled analysis of a 31-member global climate model (GCM) ensemble projection was used to estimate air temperature increase for each assessed period, and the CBP partnership's newly developed Phase 6 Watershed Model was used to project future changes in river discharge and nutrient loading. The CBP partnership's estuarine water quality model, CH3D-ICM, was used to simulate response of water quality to climate changes in terms of dissolved oxygen (DO) concentration, hypoxic volume, and water quality standard attainment. In addition to forcing from the GCM ensemble air temperature projection, river flow, and nutrient loading from the watershed model, sea level rise and changes in water temperature and salinity were applied at the open boundary based on the literature. The model scenarios showed that air temperature and heat flux increase has the most impact on water quality due to decreased DO solubility and increased stratification and biogeochemical processes. However, a significant portion of the adverse influence of climate warming on water quality is balanced by sea level rise, which improves water quality due to increased gravitational estuarine circulation and renewal of bottom water where hypoxia occurs. Even with this positive effect of sea level rise, water quality is projected to degrade under climate change conditions. By 2025 the current estimates are that nonattainment of DO water quality standards in the deep channel of the Bay will increase by 2% under the Total Maximum Daily Load (TMDL) condition, which is equivalent to about 9 million pounds of nitrogen reduction from the watershed. Results, analysis, and management implications for future time frames will be presented.