Scientists have discovered what is causing the recent increases in destructive urban flooding.
A recent study showed flooding risk is greatest for cities along the Atlantic and Gulf coasts, where strong storm surges combine with heavy rainfall, the University of South Florida reported. Rising sea levels are still the main driver of increased flooding, but storm surges that favor high-rainfall regions greatly exacerbate flood potential.
"Nearly 40 percent of the U.S. population resides in coastal counties," said study lead author Thomas Wahl of the University of South Florida College of Marine Science and the University of Siegen in Germany. "Flooding can have devastating impacts for these low-lying, densely populated and heavily developed regions and have wide-ranging social, economic and environmental consequences."
The researchers determined the three key mechanisms behind urban compound flooding were: "elevated water levels in estuarine regions; storm surge flooding that worsens with heavy rainfall and; moderate storm surge that blocks or slows down drainage."
The team concluded the interaction between storm surge and precipitation can worsen or even trigger flooding in coastal zones and the damage it imposes. To make their findings, the researchers collected and analyzed data sets for storm surge and rainfall across 30 U.S. cities along the Atlantic, Gulf and Pacific coasts. The data spanned from the 1950s, to the beginning 20th century for some sites.
When looking at data for New York City, the researchers determined storm surges in the region were accompanied by heavy precipitation. They also found the massive flooding caused by Hurricane Sandy in 2012 was a result of was the result of extreme storm surge, and the rainfall during the storm was actually relatively light.
"Our results demonstrate the importance of assessing compound flooding and its links to weather and climate, but we need more research at local scales to determine impacts," concluded Wahl and his colleagues. "That research will require complex, integrated modeling experiments that investigate surface and drainage flows and include storm surge, rainfall and river discharge. In light of climate variability and change, it will be important to develop a detailed understanding of future patterns of storm surge and high precipitation amounts occurring in tandem."
The findings were published in a recent edition of the journal Nature Climate Change.
