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August 28, 2012 

Latest Science on Climate Change, Coastal Flooding, Hurricanes

The first big storm of hurricane season in the North Atlantic often prompts people to narrowly focus on a storm’s wind speed and category ranking. This year, coastal residents are paying closer attention to storm surge projections, which are often a better indicator of a storm’s destructive power. Importantly, hurricanes also deliver drenching rain that can lead to flash flooding. The Intergovernmental Panel on Climate Change’s (IPCC) 2012 assessment report on extreme events associates historical increases in coastal flooding and intense precipitation with human-driven climate change. These factors come into play when any type of coastal storm strikes, including hurricanes. Further, the concentration of people and valuable property along the coasts make them more vulnerable to all types of extreme weather.

Future Projections Show Less Frequent Hurricanes, But More Intense Ones

UCS climate scientist Brenda Ekwurzel recently reviewed the factors that affect the intensity of tropical cyclones, the general name given to hurricanes and typhoons. Warmer ocean water, for instance, increases tropical cyclone intensity. Meanwhile, high vertical wind shear can cause tropical cyclones to lose intensity and dissipate. Future projections of a warming climate tend to show a decrease in the frequency of tropical cyclones globally. Findings regarding future tropical cyclone intensity vary by region. A recent review found that all studies examined projected increasing intensity in the West Pacific ocean basin. Most studies showed a similar pattern for the Atlantic Ocean basins. Meanwhile, study conclusions for the East Pacific and North Indian Ocean basins were less clear.

When the IPCC examined the evidence linking human-driven climate change to the past fifty years of extreme weather, it found some of the strongest evidence for links to coastal flooding and more intense precipitation. The findings for tropical cyclones were less clear, in part, because of a lack of robust historical data over a long enough time period.

Rising Sea Levels Are Already Making Storms More Dangerous

As sea levels rise due to climate change, storms have a higher “jumping off point” and are able to penetrate further inland before they dissipate, posing greater risks to roads and buildings. Sea levels will continue to increase as the ocean warms and expands and as land-based glaciers and ice sheets melt. One recent study estimates that total sea-level rise by the end of the century could be between 2.5 feet and 6.6 feet, though scientists consider the worst-case scenario less likely.

Climate Change is Driving More Intense Precipitation

Warmer air holds more moisture and climate change is shifting precipitation toward the heaviest storms where rain occurs. Heavier rains, in turn, can drive more flooding. Since 1958, the amount of rain or snow falling in the heaviest one percent of storms has risen nearly 20 percent on average in the United States and 67 percent in the Northeast. Few studies attempt to isolate the influence on rain associated with hurricanes. However, those that have, such as high-resolution models that examined the potential impact of climate change on hurricanes project that by the end of this century, precipitation rates could increase, on average, 20 percent within 62 miles of the hurricane center.

Economic, Public Health Threats for Coasts

Coastal communities typically endure the cost of recovery from extreme weather, especially if they are unable or unwilling to prepare. They also can invest in preparedness measures to curtail the consequences of extreme weather.

Natural preparedness measures, such as restoring coral reefs and coastal wetlands can be less expensive than hard engineering projects, such as levees. Elevating a single-family home, for instance, by 24 inches could cost $22 to $62 per square foot, while raising larger structures can be far more costly. Estimates of the cost of protecting coastal areas with seawalls vary considerably. One estimate pegs the cost of seawalls for urban areas in the Northeast at $3.4 billion. However, seawalls would be ineffective against permanent flooding caused by sea-level rise without constant pumping of rain and groundwater within the walled areas. Further, vertical seawalls typically enhance erosion on the ocean side, creating higher costs for beach replenishment. 

Finally, flooding creates several public health threats that sometimes go unnoticed, from the direct threat flooded, slow-to-drain roadways pose to drivers, to more indirect threats such as waterborne diseases, sewage overflows, and household mold.

As climate change continues, localities will have adjust their response plans to take into account the increasing flooding risks associated with rising seas and intense precipitation. These risks affect all coastal communities, including those that are hit by tropical cyclones.


The Union of Concerned Scientists puts rigorous, independent science to work to solve our planet's most pressing problems. Joining with citizens across the country, we combine technical analysis and effective advocacy to create innovative, practical solutions for a healthy, safe, and sustainable future.

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