Scientists know that extreme precipitation events and subsequent severe flooding are likely to increase across North America in future decades – becoming more intense, happening more frequently, and causing property damage and loss of life. Recent studies show that high streamflow and once-in-a-lifetime floods are expected to increase significantly in the future in the Midwest.
Despite this, studies of flood inundation stemming from extreme precipitation had yet to be conducted for Ohio’s Central Lake Erie Basin – an area with communities susceptible to flooding and unique weather patterns that differ from other parts of the country.
Researchers assessed future flooding extents for two river basins in Northeast Ohio: the Grand River and the Chagrin River.
Building off a previous Ohio Sea Grant study, a team of researchers from Youngstown State University set out to address this knowledge gap. The new project, funded by an Ohio Sea Grant small grant, assessed future flooding extents for two river basins in Northeast Ohio, the Grand River and the Chagrin River.
Results from the study will help provide communities and local governments with accurate information to prepare for future flooding impacts, said Suresh Sharma, an associate professor in Youngstown State’s Civil and Environmental Engineering Program, who led the study.
“This study offers a comparative analysis between different environmental scenarios, providing a broader perspective on potential future flood risks, particularly on the Lake Erie Basin,” Sharma said.
In the team’s previous project, which focused on using green infrastructure to reduce stormwater runoff, researchers developed an intensity duration frequency (IDF) curve, a graphical tool that describes the likelihood of a range of extreme rainfall events. For this recent project, they were able to use that curve alongside environmental data accounting for different greenhouse gas emissions scenarios in the near and far future. From there, the team used models from the U.S. Army Corps of Engineers Hydrologic Engineering Center to simulate hydrologic and hydraulic processes.
The result: a model that can predict peak discharge, or the maximum rate of water flow in a river or stream, as well as the extent of flooding over a given area – across different emissions scenarios and return periods. A return period is the average number of years between floods of a certain size.
“So a 100-year return period means that the storm is very unlikely to occur,” Sharma explained. “The probability of having such rainfall is one percent.”
Results from the modeling found a consistent increase in peak discharge, ranging from 6% to 70% in the Grand River and 12% to 57% in the Chagrin River, across all return periods and emissions scenarios.
“This study offers a comparative analysis between different environmental scenarios, providing a broader perspective on potential future flood risks, particularly on the Lake Erie Basin.”
Dr. Suresh Sharma
For scenarios with high greenhouse gas emissions, the amount of geographic areas in the region inundated by floods increased significantly, ranging from 15% to 25% in the near future and 22% to 36% in the far future, Sharma’s team found.
Additionally, the study examined how the size of watersheds affects the extent of flooding. Results showed that larger sub-watersheds generally showed a greater percentage increase in flood inundation area compared to smaller sub-watersheds for a 100-year return period flood.
Findings will inform various stakeholders in the area, particularly the Chagrin River Watershed Partners, a nonprofit organization that needs future predictions of river flooding to determine if its existing suite of model regulations for natural resource protection needs to be updated.
“Chagrin River Watershed Partners was very helpful and supported us in providing the data and information for conducting this research,” Sharma said.
The team also aims to inform local government representatives, improving their ability to mitigate future increases in flooding. The project notably yielded two peer-reviewed journal articles, which have already been accepted for publication in the Natural Hazard Review Journal of the American Society of Civil Engineers.
Ohio Sea Grant is supported by The Ohio State University College of Food, Agricultural, and Environmental Sciences (CFAES) School of Environment and Natural Resources, Ohio State University Extension, and NOAA Sea Grant, a network of 34 Sea Grant programs nation-wide dedicated to the protection and sustainable use of marine and Great Lakes resources. Stone Laboratory is Ohio State’s island campus on Lake Erie and is the research, education, and outreach facility of Ohio Sea Grant and part of CFAES School of Environment and Natural Resources.