Investigating the Sensitivity of U.S. Streamflow and Water Quality to Climate Change: U.S. EPA Global Change Research Program’s 20 Watersheds Project

Abstract

The U.S. EPA’s Global Change Research Program (GCRP) recently began an effort to address gaps in the current knowledge of the sensitivity of U.S. streamflow, nutrient (nitrogen and phosphorus), and sediment loading to potential future climate change, and the methodological challenges associated with integrating existing tools (e.g., climate models, land-use models, watershed models) and data sets to address these scientific questions. The study is based on watershed modeling in 20 large U.S. watersheds. The purpose of this paper is to describe the overall structure of this ongoing effort—methods, sites, models, and scenarios—and discuss preliminary results generated to date for a subset of the watersheds. Specifically, a representative set of modeling results are reviewed that encompass the full suite of sensitivity tests explored in this project. These results illustrate a number of key methodological issues, sensitivities, and uncertainties associated with carrying out these types of climate change/hydrologic impacts assessments, including: the sensitivity of simulated changes to the watershed model used; the sensitivity of simulated changes to climate model and downscaling approach used; and the interaction between climate change and other key forcing factors, specifically urbanization and change in atmospheric CO2 concentration. In addition, this suite of results provides an overview of the response to climate change in different geographic regions and the different sensitivities of a variety of flow and water quality end points.