This post belongs to a special series of posts written by students in Dr. Simon Engelhart’s Coastal Geologic Hazards course at the University of Rhode Island. In this course students learn about coastal processes, including storm surges and sea level rise, and how these impact people and the environment.
If you live along the coast you might have personally felt the effects of coastal storms. Even if you don’t live by the coast it every year the news constantly reports on new hurricanes forming in the Atlantic between June 1st and November 30th. Talk of “how we are due for a catastrophic event” builds and every year the east coast grows restless; will this be the one? Unfortunately, we probably won’t be able to answer that question until after it happened. This article will examine three different, recent articles that help us answer three questions: Are we witnessing the most active hurricane season through time? Is human induced climate change going to create more storm damage? Can powerful storms act more like a tsunami than a hurricane as storms intensify with climate change?
Before these questions are answered, it is important to give a little background and to explain what factors contribute to a storm’s strength. The main requirement for tropical cyclones, which include hurricanes and typhoons, to intensify is presence over warm water. The biggest factor in determining storm damage is wind. Not only does wind cause damage in itself, but it is also the largest contributor to something called storm surge. Storm surge, or how much water the storm winds will push and how much abnormal rise the water will increase above the normal predicted tide, can bring massive flooding. Recall back to when you were a kid in a pool and you would push water with the palm of your hand. Simply speaking that is surge, in this case ‘palm surge’. Surge can cause more damage along the coast than wind. Fetch, the area affected by the storm’s winds, also dictates the power of a storm, since the area the larger the area the wind blows across, the more space the storm can gather strength from. For example, Hurricane Sandy was only a Category 3 hurricane, but because its fetch covered almost the entire east coast of the United States, the surge was much worse relative to other Category 3 hurricanes.
Sea-level rise will cause intensifying flooding from storm surge in New York City
Since hurricanes derive all their energy from moisture that comes off warm ocean water, as sea-levels rise could that intensify hurricanes? Research suggests that storms may become more powerful and possibly more frequent. At the very least, could areas that are suffering from higher sea-levels suffer more damage at the hands of a hurricane which can add more water to these already inundated areas? To answer these questions Andrea J. Reed from Penn State University and her team carried out an assessment for New York City. In their article ‘Increased threat of tropical cyclones and coastal flooding to New York City during the anthropogenic era’, they discuss that the sea level in New York rose by 1.24 m since 850 AD, and the rising rate is about six times higher in recent years than the period of 850 to 1800 AD. Andrea and the team also found that relative sea-level rise is the major factors for coastal flooding in NYC. Once you combine a higher sea level with storm surge, you have the potential for much more damage from floods. In fact, the findings presented evidence that flood heights are significantly greater in the present day than ever before with more intense storms that produce higher storm surges.
But are storms getting more frequent now more than ever?
Michael Mann of Penn State compared data from Atlantic hurricanes that made landfall by looking at sediment cores to data compiled from previously published statistical models of Atlantic tropical cyclone activity. Both methods of hurricane reconstructions since AD 500 revealed evidence of a peak in Atlantic hurricanes during medieval times (around AD 1000) which was then followed by a lull in hurricanes. This medieval peak almost rivals recent levels of activity. However, the medieval peak was most likely caused by a relative Atlantic warming caused by something called “La-Niña,” a weather phenomenon that causes radical global weather change every 2-5 years on average.
So, what could storms possibly be like in the era of Atlantic warming caused by human activities? Storms could be so powerful that they resemble characteristics of a tsunami. Typhoon Haiyan which hit the Philippines in 2013, for example, was the most intense and fastest moving storm worldwide to date. Typhoons are hurricanes that occur in the Pacific and because storm surge can cause large waves, they are unlike tsunamis in that tsunamis are caused by earthquakes or avalanches. An international research team led by Janneli Soria of Nanyang Technological University in Singapore found evidence that Typhoon Haiyan had shared features of a tsunami and typhoon. By studying the deposits left by Typhoon Haiyan in towns around the Leyte Gulf, Philippines, the team was able to determine some characteristics of the storm. For example, the team studied how far inland the storm reached by looking how far sand deposits went.
What can forensic science of coastal environments tell us about storms?
The team found that the surge caused by Typhoon Haiyan moved as fast as a tsunami at 3 to 7 meters per second. To put that into perspective, 7 meters per second is about 16 miles per hour. Usain Bolt’s average speed in his 2008 Olympic performance was 27 miles per hour. In other words, at best, he would have been able to outrun the surge wave for only 200 m before it would eventually catch up to him. The team also found that coastal storms usually leave deposits less than 100 meters inland. Typhoon Haiyan, like many tsunamis, was able to deposit sediment up to one kilometer inland. Usain Bolt wouldn’t have stood a chance.
To make matters worse for the people that were affected, the team found that the surge came in waves. Witnesses say that there were three different waves that inundated the coast, but the team only found two deposits, indicating there were only two different waves. The damage was not evenly spread across the coastal areas though. Areas with steeper slopes had the thinnest deposits that also did not reach far inland. Flatter, less vegetated areas or even depressed areas had the thickest deposits that went the farthest inland.
There is no question that the climate is changing and sea level is rising as a result of human induced activity. The evidence that exists demonstrates that climate change and sea-level rise will cause more powerful coastal storms which feed on warmer waters. This will increase damage to coastal areas as a result of increased flooding and storm surge. Is the Atlantic east coast prepared to handle a tsunami-like hurricane? You can read about some proposed and already implemented storm preparations in this article.
Omar Fahmy is a Masters of Environmental Science Management Student at the University of Rhode Island. Omar is also a professional stone mason. When not working Omar enjoys surfing and spending time with his family and friends on the southern coast of Rhode Island.
Jeeban Panthi is a Ph.D. student at the University of Rhode Island and is pursuing his research on saltwater and groundwater interaction in Southern Rhode Island. Like water flows from mountain to ocean, Jeeban worked a few years in the mountain region (Nepal) and then came to Rhode Island for his study. He has had a few opportunities to go on glacier expeditions and white water rafting in rapidly flowing rivers. In his free time, he loves visiting new places, hiking, gardening, and reading and reviewing journal papers.
Logan Thomas is a senior undergraduate at the University of Rhode Island pursuing a degree in geology with interests in the GIS field.
Feature image: A ship that was swept by Typhoon Haiyan to downtown Tacloban city in central Philippines November 21, 2013. Typhoon Haiyan smashed into the central Philippines on Nov. 8 killing at least 4,000 people and reducing most of what was in its path to matchwood and rubble. Source.
Mann, M. E., Woodruff, J. D., Donnelly, J. P., & Zhang, Z. (2009). Atlantic hurricanes and climate over the past 1,500 years. Nature, 460(7257), 880.
Reed, A. J., Mann, M. E., Emanuel, K. A., Lin, N., Horton, B. P., Kemp, A. C., & Donnelly, J. P. (2015). Increased threat of tropical cyclones and coastal flooding to New York City during the anthropogenic era. Proceedings of the National Academy of Sciences, 112(41), 12610-12615.
Soria, J. L. A., Switzer, A. D., Pilarczyk, J. E., Siringan, F. P., Khan, N. S., & Fritz, H. M. (2017). Typhoon Haiyan overwash sediments from Leyte Gulf coastlines show local spatial variations with hybrid storm and tsunami signatures. Sedimentary Geology, 358, 121-138.