Effectiveness of Best Management Practices with Changing Climate in a Maryland Watershed

The potential impacts of climate change on BMP effectiveness were investigated using SWAT simulations for an agricultural watershed that drains into the Chesapeake Bay in the U.S. Northeast climate region. Critical source areas (CSAs) for sediments, nitrogen, and phosphorus, identified for current and future climate (SRES scenarios A1B and A2), were classified by density to support BMP prioritization schemes. BMPs were designed for these CSAs and tested against current and future climate using SWAT simulations to evaluate their robustness. A second set of BMPs was designed by optimization for all agricultural and urban lands in the study watershed and was similarly tested for robustness. In both cases, the design goal was for the watershed's water quality response to meet the bay TMDLs once BMPs were implemented. Results indicated that density 2 and 3 CSAs (hotspots exporting excess amounts of 2 or 3 constituents) may be good prioritization targets, but reaching the bay TMDLs would still require targeting all CSAs. BMPs designed for CSAs under current climate were effective to reach bay TMDLs under current climate but not under scenarios A1B and A2. BMPs designed for CSAs under scenario A2 were effective to reach the bay TMDLs under all climates, except for nitrogen under A2. Similarly, BMPs optimized for agricultural and urban lands, when designed for current climate, were effective in meeting TMDLs for current climate only. Optimizing these BMPs for future climate produced a design that met TMDLs under both current and future climates, except for nitrogen with future climate. However, in this case, the nitrogen TMDL was exceeded by a smaller amount than in the CSA design. It was concluded that, in the U.S. Northeast, BMPs designed to remediate water quality problems under current climate will be insufficient to maintain water quality with climate change. Increased annual rainfall and storm intensity will increase the proportion of watershed area needing BMPs, and current hotspots will generate excess amounts of new constituents that will require re-design of existing BMPs. Community-based participatory strategies will likely be required to foster BMP adoption and sustain water quality gains in the Chesapeake Bay region.