An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

About the 20-Watersheds Tool

Future warming temperatures and changes in precipitation will have direct and cascading effects on water quality. Effects will vary in different regional and watershed settings, and in some locations are anticipated to lead to an increased risk of water quality impairment. This site contains summaries of watershed simulation results as a supplement to the EPA report "Watershed Modeling to Assess the Sensitivity of Streamflow, Nutrient, and Sediment Loads to Potential Climate Change and Urban Development in 20 U.S. Watersheds" (EPA/600/R-12/058F).

The results characterize the sensitivity of streamflow, nutrient (nitrogen and phosphorus), and sediment loading in 20 large, U.S. watersheds to a range of plausible mid-21st century climate change and urban development scenarios. Study areas were selected to represent a range of geographic, hydrologic, and climatic characteristics. Watershed simulations were conducted using the Soil Water Assessment Tool (SWAT) model.

Scenarios of future climate change are based on dynamically downscaled (50x50 km2) output from four of the Global Climate Models (GCMs) used in the Intergovernmental Panel on Climate Change (IPCC) 4th Assessment Report for the period 2041-2070 archived by the North American Regional Climate Change Assessment Program (NARCCAP). Urban and residential development scenarios representative of mid-21st century (2050) for each study area were based on projections from EPA’s national-scale Integrated Climate and Land Use Scenarios (ICLUS) project. Results are expressed in native units and as future changes relative to baseline conditions, but are most robust when expressed as future changes.

A detailed description of the methods and results of this study is available in the EPA Report. Users should also refer to this report for a description of modeling assumptions and limitations.

Top of Page

History of 20-Watersheds

Below is a list of important milestones to the Global Change Explorer (GCX) Watersheds Tool.

Date Milestone
Apr 2018 Watersheds was incorporated into the Global Climate Explorer set of tools.
Mar 2017 EPA released the Watersheds v.1 interactive tool for viewing and accessing Soil Water Assessment Tool (SWAT) simulation datasets on the EPA website.
Sep 2013 EPA released the final report,  Watershed Modeling to Assess the Sensitivity of Streamflow, Nutrient, and Sediment Loads to Potential Climate Change and Urban Development in 20 U.S. Watersheds and SWAT simulation datasets associated with the report.
Mar 2013 EPA released an external review draft report for external peer review and public comment. [Federal Register Notice Mar 1, 2013]
Jan 2009 EPA initiated a project to produce a 20-Watersheds report.

Top of Page