20 Watersheds Report

Around the Water Cooler: Watersheds and Climate Change

To celebrate Earth Day, all this week and into next we will be highlighting EPA climate change research with Science Matters feature articles. Today’s “Around the Water Cooler” addition illustrates the connection between climate change and water.

Climate Change and Watersheds: Exploring the Links
EPA researchers are using climate models and watershed simulations to better understand how climate change will affect streams and rivers.

A warming climate threatens hotter summers and more extreme storms. We know we may need to upgrade our air conditioning systems and make emergency preparedness kits, but aside from temperatures and storms, what are other ways we will be affected by climate change?

Map showing the 20 watersheds EPA researchers studied. Click on the image for a large version.

EPA water scientists and their partners are studying how climate change may affect watersheds—the network of rivers and streams that feed into larger water bodies such as big rivers, lakes, and oceans. A recent EPA report, referred to as the 20 Watersheds Report, combines climate change models and watershed simulations to develop a better understanding of what changes to streams and rivers we might expect over the next several decades.

“A key thing that’s unique about this work is the scope; we applied a consistent set of methods and models to 20 large watersheds throughout the nation,” says lead scientist Tom Johnson.

Johnson’s team of researchers used different climate change scenarios to model changes in streamflow volume and water quality in the 20 chosen watersheds.

“Climate can be defined loosely as average weather,” Johnson explains. “Climate change scenarios describe potential future changes in climate, like temperature or precipitation.”

For a given climate change scenario, watershed simulations were used to determine changes in streamflow (the actual volume of water running through the streams) and in nutrient and sediment pollution levels.

In addition to climate change scenarios, researchers also took into account urban and residential land development scenarios in their watershed simulations. The ways people use and alter the land (such as building roadways, parking lots, etc) will also have an impact on water resources. The land development scenarios used were based on projected changes in population and housing density in the study watersheds.

Research results show a great variety in watershed responses to climate and urban development scenarios in different parts of the country. Generally, simulations suggest certain trends for streamflow: that flow amount decreases in the Rockies and interior southwest, but increases in the northeast. Results also show higher peaks in streamflow that can increase stream bank erosion and sediment transport, as well as potentially increase nutrient pollutants. Overall, the research shows that the potential changes in streamflow and water quality response in many areas could be very large.

“This information can be used by water managers to better understand if and how things like water quality and aquatic ecosystems might be vulnerable, and to help guide the development of response strategies for managing any potential risk,” says Johnson.

For example, where water is suggested to be scarce, managers can plan alternative water supply methods; where water is expected to become highly polluted from nutrients and sediment, managers can take action now to limit the actual impact of these pollutants on the water resource.

The findings of EPA’s 20 Watersheds Report will help water and resource managers recognize the changing conditions of streams and rivers and identify any future conditions that may need addressing.

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EPA Climate Change Research

EPA Water and Climate Research

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action.

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Get to Know a Watershed Near You

By Alexandra Soderlund

It’s clear that climate change is an issue society will face in the coming century, but we don’t always know what the effects of climate change will be. It’s easier to plan ahead and prepare if we know what types of changes may be possible.

Recently, a group of EPA scientists and collaborators did just this, using models—not the models you see on fashion runways, but computer modeling tools—to learn how different future climate change scenarios could affect our water.

EPA researchers used a cool model with a cool name—SWAT (or the Soil and Water Assessment Tool) as one tool in their recently released draft 20 Watersheds Report. The model can be used to predict the impact of land management practice on water and sediments in watersheds, and they used it to gain a better understanding of the sensitivity of streamflow and water quality to the impacts of climate change.

Map from the "20 Watersheds Report." Copies of the draft are available in the "Download" section at: http://1.usa.gov/XsCiMU.

A watershed is an area of land where all the water that drains off of it or from under it goes into the same place. To develop the 20 Watersheds Report, EPA looked at things like streamflow, nutrient (phosphorous and nitrogen), and sediment loading and, using computer models, projected how these attributes might be affected by different future climate change scenarios.

There are a couple of things that make this report really exciting. First, the scope of the report is much bigger than a lot of what’s currently out there. The 20 watersheds in the title refer to watersheds all over the U.S. in each of EPA’s ten geographic regions. So it’s quite possible you live near one of these watersheds. Second, the report presents important methodological protocols for such work. Using the same models and measures to look at a broad range of areas is very useful. It helps to set a standard for comparison.  Without standards, things can be confusing (take this from an Australian who has been living with the Imperial measurement system for a while).

The draft watersheds report, when final, and the tools and methods it generates, are going to be really useful as a jumping off point for further and more focused research.

About the Author:  When not interning at the EPA, Alexandra Soderlund studies at the University of New South Wales (NSW) in Sydney, Australia. She is majoring in media/technology and genetics, and is also the online coordinator for the NSW branch of the Australian Youth Climate Coalition.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action.

Please share this post. However, please don't change the title or the content. If you do make changes, don't attribute the edited title or content to EPA or the author.