Across America, infrastructure built to handle peak stormwater flows from streams and rivers have been engineered under the assumption that rainfall averages stay constant over time. As extreme weather events become more frequent, these systems could be in trouble.
But they don’t have to be, say researchers at the University of Virginia whose recent study examines how climate change will intensify rainfall and what that means for roads, bridges and water management systems. The research, which used advanced hydrodynamic computer modeling methods, provides vital new tools to help engineers adapt infrastructure for these changing conditions.
It also addresses an understudied area by looking specifically at how impacts from climate change-driven increases in precipitation and streamflow vary across watersheds of different sizes. For example, how would the area that drains into Virginia’s Rivanna River — about 750 square miles — fare compared to one of its feeders, Moore’s Creek, with a watershed of just 35 square miles?
“By developing models that connect climate change to infrastructure vulnerability, we hope to offer practical solutions for resilient infrastructure,” said Jonathan Goodall, a professor in the Department of Civil and Environmental Engineering.
The team, led by Goodall’s former Ph.D. advisee Mohamed M. Morsy, now an associate professor at Cairo University in Egypt, published their findings in the Journal of Hydrologic Engineering.
Smaller Watersheds Are More Vulnerable
The researchers focused on Virginia’s Coastal Plain as a test case. The study found that smaller watersheds are particularly vulnerable to climate change, experiencing sharper increases in peak streamflow. With less land to absorb rain, water flows into streams more quickly, causing a surge in streamflow.
Larger watersheds, by contrast, have a “dampening effect,” with the percent rise in streamflow decreasing as the watershed size increases. However, the overall flood risk will still increase, particularly under the worst-case climate scenario the researchers used in their computer models. In this worst case, greenhouse gas emissions rise significantly, leading to severe global warming and more extreme weather.
The impact on smaller watersheds is significant, and it underscores the need to rethink our infrastructure designs.
“The impact on smaller watersheds is significant, and it underscores the need to rethink our infrastructure designs,” Goodall said. “What we’ve found is that climate change may cause a 10-40% increase in rainfall intensity by 2085, depending on the scenario. Engineers will need to incorporate these changes into their calculations for bridges, culverts and other hydraulic structures.”
‘No Longer Optional’
The study analyzed future rainfall predictions across 29 weather stations in the state. Then they used the Two-Dimensional Unsteady Flow hydrodynamic model, known as TUFLOW, which simulates water flow over landscapes, to assess future conditions in Virginia’s Coastal Plain. These computer simulations, commonly used in flood management, show how water will move during extreme weather events.
Under moderate to severe climate scenarios, the increase in rainfall intensity ranged from 10-30% by 2045 and 10-40% by 2085. This could lead to a nearly 50% increase in peak streamflow in smaller watersheds, which are less able to manage sudden flood surges.
One key advance of this research is the development of new regression equations, mathematical formulas that estimate peak streamflow based on watershed size, future rainfall projections and climate scenarios.
“This will help decision-makers prioritize infrastructure upgrades and ensure that new projects are resilient against the changing climate,” Goodall said.
The work also emphasized the importance of forward planning.
“The study shows that climate change adaptation is no longer optional,” Goodall said. “These insights will be especially important for engineers and policymakers responsible for critical infrastructure in coastal areas, where flooding risks are high.”
Publication
The paper, "Quantifying the Impact of Climate Change on Peak Stream Discharge for Watersheds of Varying Sizes in the Coastal Plain of Virginia," was published online March 30 for the June 2024 issue of the Journal of Hydrologic Engineering.
Binata Roy, Yawen Shen, Alexander B. Chen and Faria T. Zahura, all of UVA Department of Civil and Environmental Engineering, and UVA Ph.D. alumnus Jeffrey M. Sadler, now an assistant professor at Oklahoma State University, contributed to the research.
The project was funded by the Virginia Transportation Research Council.
