USDA-UM Studies Climate Impacts on Watersheds

A U.S. Department of Agriculture-funded study done at the University of Massachusetts Amherst shows that rising temperatures due to climate change will reduce the availability of water in the Connecticut River Watershed during the summer when demand is highest and increase sediment and pollution loads carried by rivers and streams. The river serves as Greater Boston's primary water supply and is home to thousands of species of plants and animals in a national Fish and Wildlife Refuge.

Changes in the watershed will add to existing pressure on ecosystems and have important consequences for agriculture, forestry, fisheries and water supplies. Results of the study were published earlier this year online in Climatic Change.

"The response of watershed systems is a new area of climate change research, and the U.S. Environmental Protection Agency is calling for proposals to study this issue," says Timothy Randhir, a professor of natural resources conservation. "With additional funding, I hope to expand this research to the national level." Graduate student Eric Marshall co-authored the study.

"Fortunately, sound land-use planning can help protect the watershed, including the maintenance of forests in urban areas, reducing loss of open space throughout the watershed and protecting flood plains," says Randhir. "Low-impact development and smart growth principles can go a long way in our ability to handle climatic impacts."

"Communities will need to plan for water stress months and implement water conservation practices throughout the year," says Randhir. "Water harvesting along with a network for upland storage could help manage water resources, and maintaining vegetation along streams will provide a buffer between surface runoff and sensitive streams."

Computer models used to predict changes over the next 40 years showed a decrease in the annual amount of water running off the surface of the land to feed streams and rivers in the watershed, which contains 390 towns and cities and an estimated 2.3 million people. Large changes in the timing of this runoff were also predicted.

"Typically, we see precipitation held as snow throughout much of New England in winter, and a slow release of water during the spring melting season. But warmer temperatures associated with climate change will change this pattern," says Randhir. "This is expected to decrease the annual snowpack and can cause large increases in runoff during the winter months, especially January. Systems that handle stormwater in urban areas will have to add extra capacity to avoid being overwhelmed by flooding."

Warmer temperatures were predicted to decrease runoff by up to 71 percent in the late summer months of July and August when demand is highest, resulting in reduced stream and river flows that could threaten community water supplies and the production of power at 16 hydroelectric dams located on the Connecticut River. Lower water levels in streams and rivers would mean less water for agriculture and make it more difficult to navigate rivers.

Many species of animals may have trouble adapting to the change. "Fish need adequate water flowing in rivers and streams in order to migrate," says Randhir. "We can expect to see severe strains on spring fish runs, and changes in the watershed also will increase environmental stress on other species including mammals and birds."

Randhir expects water quality to decrease as surface temperatures rise. Sediment loads carried by rivers and streams were predicted to rise by 50 percent between June and October while the volume of waters receiving the sediment decreased. In addition, changes in the watershed will alter the balance of key nutrients such as nitrogen and phosphorus, resulting in more frequent and intense blooms of algae and increased growth of aquatic plants.

Stormwater systems in urban areas will have to plan for the added sediment and pollution, and greater amounts of sediment will be carried into Long Island Sound, where the Connecticut River meets the sea. Higher sediment loads and pollutant levels could also impact the ability of fish to migrate, and place additional stress on aquatic ecosystems.

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