21 September 2016

As Hurricanes Become More Intense, Flood Risks Escalate

Researchers evaluated how changes in hurricane intensities may impact the future risk of coastal flooding on the U.S. Gulf and Florida coasts.


A hurricane’s strength is primarily dependent on its surrounding environmental conditions, like temperature or humidity. Using climate models to predict future conditions, researchers found that Atlantic hurricane intensity could increase by up to five percent in the next hundred years. Scaling up historical hurricanes to the projected levels of intensity showed that storm surges could rise anywhere from 25 to 47 percent in the Gulf and Florida coasts. This novel approach can also be used to predict hurricane intensities and flood levels around the world.


Coastal populations in the tropics and sub-tropics are vulnerable to devastating impacts of hurricane storm surges. This risk is expected to rise under the influences of climate change. Understanding the risk will be particularly important for the North Atlantic where observations show the largest upward trends for hurricane maximum winds in recent history. The impacts of increased hurricane intensity may be further magnified by a wide and shallow continental shelf along the U.S. east and Gulf coasts, combined with some of the highest rates of observed sea-level rise. Having a simple, reliable method to determine how hurricane intensity and flooding will increase is important before regional decision-makers can plan possible mitigation activities.


The Department of Energy’s Pacific Northwest National Laboratory research team developed a new approach to estimate future changes in hurricane intensity using a technique called thermodynamic Potential Intensity (PI) and a statistical downscaling method. Theoretically, PI is the calculated maximum intensity that can be attained by a hurricane under prevailing environmental conditions. The team used output from 10 different coupled climate models belonging to the CMIP5 archive to estimate mean PI conditions experienced by hurricanes under historical (1981-2000) and future climate conditions (2081-2100, using the Representative Concentration Pathways, or RCP 4.5 intermediate range emissions scenario). Combining these estimates projected that the maximum intensities for Atlantic hurricanes will increase by 1.8–4.2 percent (mean) and 2.7–5.3 percent (lifetime) by the year 2100. The team applied these projections to five historical hurricanes that made landfall over the Gulf of Mexico and Florida coasts to evaluate the impact on future storm surge risk: Frederic (1979), Alicia (1983), Erin (1995), Opal (1995) and Jeanne (2004). The results, based on simulations with the Sea, Lake and Overland Surges from Hurricanes (SLOSH) model indicate that the median storm surge will likely increase by 25–47 percent with the intensification of hurricanes contributing about 10 percent of that due to sea-level rise.

Ruby Leung
Pacific Northwest National Laboratory (PNNL)