Researchers at the University of Massachusetts Amherst recently published a study in the journal Plus Water Focusing on the Sudbury-Assabet and Concord watersheds in eastern Massachusetts, it relates hydrological changes, including floods, droughts, and runoff, to changing land-use patterns.
“We all live in watersheds,” says Timothy Rander, professor of conservation at UMass Amherst and senior author of the paper. “We are constantly modifying our landscapes, transforming what were once forests into roads, parking lots, and backyards. We are changing landscapes from one that was once hydrologically resilient to one that pushes water downstream.”
But it can be difficult to see the complex links between changes in land use and changes in the hydrological cycle. For example, much of Massachusetts is now subject to the paradoxical situation in which summer drought is followed by spring floods. Surely if there is enough excess water to flood the streets in towns across the state, should there be plenty of groundwater left for drinking, irrigating the lawn and maintaining the levels of streams and lakes?
This is where thinking like a watershed comes in. “Every raindrop has two paths when it falls,” says Randhir. “It can trickle down from the ground into a stream, or it can infiltrate the soil and flow slowly into the water table.” But by paving vast tracts of land, burying swamps and wetlands, and channeling rivers, we have made it more difficult for rain to infiltrate the soil, increasing the likelihood of drought. At the same time, all of this runoff drains into streams and rivers, which in turn becomes a flood as it flows downstream, fed by more runoff as it goes.
To make the links between land use and hydrological forcing visible, and to project these influences into the future, Randhir and his graduate student, first author Amara Taleb, focused on the Sudbury-Assabet and Concord watersheds in eastern Massachusetts, an area that includes both. rural areas and suburbs of Boston. The pair fed historical data describing changing land use into a model projecting trends for the years 2035, 2065, and 2100. The team then fed the land-use model results into a hydrological model called FORTRAN Hydrological Simulation Program.
What they found is that by 2100, total forest area will decrease by 51% and impermeable areas (roads and parking lots) will increase by 75%. These changes will increase annual flow by 3%, while surface runoff will grow by a whopping 69% annually. All this increased runoff would mean an increase in topsoil and other solids in water (a 54% increase), and a 12% and 13% increase in phosphorus and nitrogen concentrations, respectively.
But none of this should happen.
“We can plan for the future at the watershed scale,” says Randhir, through urban planning that implements best practices for sustainable, site-specific land use measures. This could include the creation of rain gardens, the use of permeable pavement in large car parks and the use of vegetable marshes to slow runoff.
“Watersheds are a sign of healthy landscapes,” says Randhir. “The quality of life in any given natural area depends on how well the watershed works.”