To help communities plan for weathering storms to come in a changing climate, EAPS scientists use novel methods to examine the behavior and impacts of hurricanes — from deep time to the present.
BY KATE S. PETERSEN I EAPS NEWS
Videos begin to apear online, one after another. Cellphone footage shot by people inside their homes, of flood water and waves crashing against the windows, of bent trees, pelted with uprooted street signs and mailboxes. The photographers pace while their homes fill with water, narrating as all the things that seemed unyielding and permanent give way.
On September 1, Hurricane Dorian struck the Bahamas as the most powerful storm to make landfall there in recorded history,joining the ranks of three other Atlantic hurricanes to have made landfall at full, devastating Category 5 strength in just the last two years, at a combined cost of over $200 billion in damage and thousands of lives. Unfortunately for those living on coasts and islands, storms of this magnitude—once a more rare occurrence—are likely to become more frequent. As a leading authority on the physics of tropical cyclones, Cecil and Ida Green Professor of Atmospheric Science and co-director of MITS Lorenz Center Kerry Emanuel puts it plainly: "Climate change, if unimpeded, will greatly increase the probability of extreme events."
And yet, in the face of this threat, coastal communities continue to grow. In talks, Emanuel points to the fact that the global population exposed to hurricanes has tripled since 1970. More information about impending storms and the damage they are likely to inflict could greatly improve outcomes for residents living in these areas, and EAPS scientists are working on novel research that will allow us in the future to more effectively predict the behavior of hurricanes and help affected communities build more resilient coastal infrastructure.
"[Our] primary goal is to better understand the processes that dictate how the ocean and the atmosphere interact within hurricanes, and hopefully be able to use that understanding to improve hurricane intensity forecasts," explains Casey Densmore,a master's student in the MIT-WHOI Joint Program.According to Densmore, warm ocean waters intensify hurricanes, powered by the extra heat. However, escalating storm winds on the ocean's surface can cause large scale water mixing, which cools the surface water and causes the storm to weaken.
If forecasters had a better understanding of this feedback loop, they could use ocean temperature data in the path of a hurricane to more effectively predict storm intensity over time, especially as it makes landfall. But to build more accurate predictive models, researchers need to first observe large scale changes in ocean temperatures in real time.
Densmore and his research team are helping to fill this data gap, having flown several missions into Hurricane Dorian aboard airplanes operated by the US Air Force 53rd Weather Reconnaissance Squadron (better known as the Hurricane Hunters) and deploying airborne expendable bathythermograph (AXBT) buoys, which sink when they hit the ocean and transmit information about the temperature profile of the entire water column.
Recent MIT-WHOI Joint Program graduate Katie Castagno PhD '19 is also a hurricane hunter, but the storms she pursues ended hundreds, maybe even thousands of years ago. While not apparent, evidence of these ancient storms can be found at the bottoms of coastal marshes and ponds.
Her strange vessel glides across the surface of a shallow coastal pond. Like some sort of technology from the movie Waterworld, it consists of canoes lashed to plywood. On top, a tripod supports a vertical, aluminum tube attached to a repurposed cement mixer engine. After finding the right spot, Castagno initializes the engine, and the tube works its way down into the sediment.
The sediment core she extracts contains a secret history: a 2,000-year timeline of heterogenous layers of deposition. Some represent organic detritus from the pond; others signify major storm events, times when blowing wind and water transported sand from nearby beaches.
While dating each layer of sediment, Castagno's research team discovered something odd: layers, representing hundreds of years, were missing from some of the cores. She suspects that these missing layers represent times that the marsh or pond was damaged by erosion, which is problematic. Coastal ponds and marshes protect inland areas from hurricane damage, and modern storms can deposit additional sediment, making them even more resilient. However, as Castagno explains,"there may be a suite of conditions [such as] one huge storm [or] several storms...that could cause this destruction, particularly as today's marshes are often increasingly degraded."
Evaluating and mitigating this type of erosion lies at the heart of Rose Palermo's research. Clicking through a few decades' worth of satellite images reveals that Barnegat Bay Peninsula, Long Beach Island, and Scituate, barrier islands located along the northeastern coast of the United States, are slowly washing away. "Barrier island erosion is a problem because there are communities that depend on them for their housing and livelihood. They also protect the mainland coast from waves and storms, and losing that barrier would put the mainland at higher risk of erosion and flooding," explains Palermo. Sea level rise driven by global climate change accelerates erosion, as do certain coastline development practices—something local residents can more easily control.
Palermo, who is also a graduate student in the MIT-WHOI Joint Program, works with a multidisciplinary team of economists, statisticians, oceanographers, and sediment transport experts to model outcomes of different shoreline interventions. Their model balances intervention costs against the property and economic damage that would be incurred by unmediated waves and storm surge.
One option she has evaluated, called "nourishing", adds sand at intervals meant to keep pace with shoreline erosion. While this is a money- and resource-intensive strategy, Palermo's model shows that certain beach nourishment regimes pay for themselves over time. "Our influence on the stability of barrier islands is dramatic, both through development on the coast and the modifications we make through beach management projects," comments Palermo.
In records tracked since 1971, each year on average tropical cyclones wreak $700 billion in damage worldwide, and have overall claimed almost half a million lives. And while these storms have all passed, researchers like Emanuel, Castagno, Densmore, and Palermo know another deadly storm is not far off. With rising atmospheric and ocean temperatures predicted to make future tempests more frequent and intense, rising sea levels will only compound the danger with potential for unprecedented storm surge and coastal flooding. To mitigate the hazards these storms present, the scientists' work to understand the processes that drive hurricane behavior is vital to informed decisionmaking for communities and policymakers—on everything from emergency preparedness and evacuation plans to sustainable engineering and urban development—pursuing the ultimate goal to protect economies, ecosystems, and human life.
Cedit: Naval Research Lab
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