Verisk Analytics company develops technique for analyzing future U.S. coastal floods

Atmospheric and Environmental Research (AER), an environmental research and development company and a Verisk Analytics business, announced on Monday that it has led the development of an “innovative, broadly applicable methodology” for analyzing future coastal floods in the United States.

As businesses and governments plan for climate change, scientists and catastrophe modellers are searching for better approaches to quantify both changes in storminess and increases in the baseline sea level. But it’s generally been difficult for scientists to analyze both of those factors simultaneously largely because that requires fusing disparate climate processes occurring at different spatial scales, AER explained in a press release on Monday.

“When you look at hazards separately, it’s bad enough, but when you consider the joint effects of two hazards together, you can get some surprises,” said Radley Horton, a climate scientist at Columbia University’s Earth Institute and study co-author, in a statement.

The newly developed technique provides a more comprehensive view of the future coastal flood hazard, in which changes are summarized using a fully probabilistic flood index. A research article, titled Joint projections of US East Coast sea level and storm surge, related to the new technique was published on Monday in the journal Nature Climate Change.

The research article highlights the U.S. East Coast, a “hot spot” of sea-level rise that is also exposed to North Atlantic basin tropical cyclones. The analysis projects a dramatic increase in flood duration and magnitude, with a late 21st century flood index up to several hundred times greater than a 1986–2005 baseline period.

“Coastal flooding could possibly shoot up several hundredfold by 2100, from the Northeast to Texas,” Columbia University added in the statement.

The article was a collaboration between Dr. Christopher M. Little, staff scientist at AER and lead author of the study and climate scientists at Columbia University, Princeton University, Rutgers University, the National Oceanic and Atmospheric Administration and the University of Iowa.

The study assesses 21st century changes in the coastal hazard for the U.S. East Coast using a flood index that accounts for changes in flood duration and magnitude driven by sea-level rise and changes in power dissipation index (an integrated measure of tropical cyclone intensity, frequency and duration). Sea-level rise and power dissipation index are derived from representative concentration pathway (RCP) simulations of 15 atmosphere–ocean general circulation models. 

The authors analyzed 15 climate models at five locations: Atlantic City, N.J.; Charleston, S.C.; Key West, Fla.; Pensacola, Fla.; and Galveston, TX. They considered both storminess and increases in the baseline sea level, and also the chances that they would be correlated. “In other words, the probability that they could act together in time to produce more than the sum of their parts,” the Columbia University statement said.

Based on this, the authors made two projections for the 21st century: one if the world greatly reduces emissions of greenhouse gases, and one if the current trajectory continues. “Even the reduced-emissions calculations suggest a 4- to 75-fold increase in the flood index—that is, the combined heights and durations of expected floods—across the five locations,” the statement said. “With business as usual, the flood index might go up 35 to 350 times. Furthermore, the study does not account for any sea-level rise caused by melting of glaciers and ice sheets—only water expansion—so that could add to the hazard.”

Dr. Little said that while several research groups have developed projections of changes in coastal floods due to sea-level rise, “the influence of changes in tropical cyclones has been difficult to quantify due to their small scale and infrequent occurrence. By focusing on the large-scale drivers of tropical cyclones and performing the analysis over the East Coast as a whole, we were able to surmount those challenges.”

What that means is that changes in sea level and storminess are combined into the same analysis, allowing researchers to assess the coastal flood risk more comprehensively. “Similar assessments of so-called joint hazards (for example, heat and humidity, or storm surge and rainfall-driven flooding) are critical to understanding the full scope of climate change risks,” Dr. Little added.