TMDL in the Context of Climate Change: Adapting Critical Condition and Uncertainty Analysis in Support of TMDL Development and Implementation

Climate change will have numerous and diverse impacts on the environment, including those on ambient water quality. In areas projected to experience decreased runoff (e.g., in many semiarid areas), water quality deterioration will be even more pronounced. The number of waterbodies recognized as “impaired” is likely to increase, even if pollution levels remain stable. However, projected climate change impacts on ambient water quality and Total Maximum Daily Load (TMDL) have been studied relatively little. The objectives of this paper are to review available TMDL-related water quality studies in the context of climate change and recommend ways in which a few key issues in TMDL programs (e.g. critical condition, uncertainty analysis) should be adapted to reinforce TMDL as an effective water quality management tool in a changing climate.This paper reviewed TMDL and water quality issues in a climate change context from several available studies that extend to different waterbody types (stream, lake, and estuary). It is important to assess the TMDL estimate and future effectiveness of a TMDL implementation plan under projected climate change scenarios as well as under different management actions in response to climate. In response to the statement that “stationarity should no longer serve as a central, default assumption in water-resource risk assessment and planning”, trade-offs need to be made between ambient water quality simulations using either long-term historical data series or stochastic predictions of such data based on properties of the historical time series. The TMDL and National Pollutant Discharge Elimination System (NPDES) programs will need to adapt by considering the long-range implications for waterbody impairment associated with climate change and make needed revisions to TMDL guidance and water quality-based effluent limitations. Ongoing studies will equip policymakers with the information and decision tools required to cost-effectively adapt to climate change impacts on TMDL and water quality management.