Hurricane Florence, which made landfall as a Category 1 storm in North Carolina in 2018, broke rainfall records and caused catastrophic 500-year flooding occurrences along the Cape Fear River Basin.
This is precisely the kind of meteorological occurrence that Z. George Xue of the LSU Department of Oceanography and Coastal Sciences (DOCS) thinks his unique coupled computer modeling approach may more accurately predict flood, helping communities prepare for disasters. As far as he is aware, only his lab employs this procedure, according to Xue.
The Hurricane Florence events were used in a paper recently published by Xue, DOCS graduate student Daoyang Bao, and the rest of their research team in the Journal of Advances in Modeling Earth Systems to show the viability of this novel technique.
According to John C. Warner of the US Geological Survey, another study collaborator, increasing the accuracy of flooding projections can aid in hurricane preparedness. “Better warnings of approaching storms can benefit coastal management,” says the statement.
According to Xue, this innovative coupled modeling technique may also have long-term advantages for communities.
“Our model can detect which location is most susceptible to compound floods and provide not only short-term projections but also scenario analyses considering potential changes in the temperature and sea level,” the author claimed.
The challenges presented by compound floods
This is what happened along the coastal flood during Hurricane Florence. In a compound flooding event, two or more causes of flooding—in this case, rivers inundated with rain and the building storm surge from the hurricane—converge to cause flood.
It is a complicated system that is challenging to model using the conventional river and ocean models since neither adequately reflects how the various sources of water interact with one another.
In linked modeling, river and ocean models are combined and run simultaneously so that one receives input from the other. This mimics the circumstances of a compound flooding event, in which a hurricane’s storm surge and rain-induced flooding from the storm’s advance inland collide over a coastal location.
Using information acquired during Hurricane Florence as a means of validating model performance, Xue and his team combined an ocean model with a river model. They compared the simulation’s results to those of a more conventional “linked” model, which runs two simulations simultaneously, and to information received from various monitoring stations in the Cape Fear region throughout the actual hurricane.
The study discovered that coupled models gave noticeably better results. At the head of the Cape Fear Estuary, simulated water levels were 20–40% more accurate than those generated by the connected model. Additionally, this is the first time that a quantitative diagnosis of the impact of storm surges and flash floods on combined flooding has been made.
This connected model, according to Xue, is a fresh development of an idea he has been working on for almost 20 years.
Building a “closed cycle” modeling system that can incorporate atmospheric, ocean, and river dynamics in the land-estuary-ocean continuum is what Xue stated he has been working on. “By combining the processes from the ocean side with those from the river and land surface, this new model closes the loop.”
