What happens when climate change or urbanization increases the frequency or severity of floods? How well can different downstream communities prepare for and respond to those catastrophic events?
USDA Forest Service scientists and approached these questions in a new way. They developed a risk matrix that pairs the likelihood of high streamflow events – which can be an indicator of flooding – with local community capacity to bear the consequences.
“We saw a limitation in models that use only biophysical factors like climate,” says Sheila Saia, currently a postdoctoral researcher with North Carolina State University. “They leave out socioeconomic factors that may impact a community’s ability to prepare, respond, and adapt. Our risk matrix links streamflow and demographic projections for the Yadkin-Pee Dee watershed in western North Carolina.”
Saia led the research as an ORISE fellow with SRS and was joined by David Wear, John Coulston, and James Vose on the study – along with several colleagues from North Carolina State University. Their results were published in Ecosystems.
The study watershed stretches across central and western North Carolina and includes the cities of Charlotte and Winston-Salem, smaller cities and towns, and rural areas. This area has seen significant population growth, and more growth is projected. About 17 percent of the 1.6 million people within the watershed live in poverty.
Socially vulnerable communities are located throughout the basin. The researchers used a social vulnerability index to represent the degree of community vulnerability. The index includes factors like age, ethnicity, and housing ownership.
The team used a biophysical model called SWAT to simulate streamflow under different scenarios for future climate, land use, and combinations of the two. Their analysis included backcasting – checking how well the model reproduces historic streamflow – to reduce uncertainty in the model and improve confidence in its results.
The researchers combined these two tools to identify smaller areas with greater potential for higher streamflow, and likely, more flooding. Their projections show more frequent extreme flows and ten-year flows, particularly in the middle and lower areas of the basin.
Some of this increased risk can be attributed to urbanization, which replaces the forests that help to absorb streamflow and mitigate flooding.
Most forestlands in the South are privately owned, and urban areas in the Southeast continue to expand. Combined, this increases the likelihood of forest land loss to development, the potential for flooding, and the need for strategic forest conservation and management.
“There’s a critical role for private and public forests in helping to decrease flood risks. This study helps identify where forests are most important for mitigating peak flows and contributing to the well-being of everyone in the Yadkin-Pee Dee basin,” says Vose.
The team hopes that local or regional water resource managers will consider these results as a starting point when planning for future climate change impacts.
“Climate change adaptation planning that relies on either biophysical or socioeconomic approaches alone may miss locations where future increases in streamflow overlap with vulnerable communities,” adds Saia. “Our risk matrix approach identifies places at risk and could help residents and other stakeholders visualize where high streamflow events might occur.”
For more information, email James Vose, who recently retired, at firstname.lastname@example.org.