by Forrest Burt
“We study the extreme sea levels of coastal locations around the world,” said doctoral student Mintaek Lee. “Outside factors – changes in the instrument, location of the measurements, earthquakes, land reclamation, dredging – all these things can influence the baseline distribution of sea levels. My research focuses on identifying the inhomogeneous shifts in their mean levels which are potentially induced by those factors, so we can rigorously estimate the long-term trends in the extreme coastal sea levels.”
Lee, a doctoral student in the Computing program looks at “change points” in extreme coastal sea levels around the world. Alongside his advisor, professor Jaechoul Lee, the two work to identify points where the mean levels shift drastically from the extreme sea level, which could be due to outside influence.
This is important because many researchers are using the same datasets to study extreme sea levels as Lee, and these change points should potentially be accounted for in their research. 70% of the data in these datasets comes collectively from the British Oceanographic Society and the University of Hawaii Sea Level Center, with the remaining 30% coming from various government agencies.
To assess his method of finding these change points, Lee uses a genetic algorithm. A genetic algorithm mimics the process of natural selection to identify change points in the extreme sea levels, but is computationally expensive. Lee considered eight different scenarios that he wanted to test in his simulation study, and needed to run the genetic algorithm 1000 times on each scenario.
“If I were running this on my computer, it would have taken anywhere between one to two hours per repetition – three weeks of straight computing on my computer. I was also impressed at how R2 was much faster than the department server. It was a steep learning curve to get up and running, but Kelly and Mike [Research Computing’s high performance computing engineers] were both really, really helpful.”
There have been prior studies that have looked into these extreme sea levels, but do not consider the change points that Lee studies. Lee found that at 52 sites worldwide, considering the change point altered the expected trend by over 40 centimeters per century. He also found many other places where considering change points altered the trend by a lesser, but still significant, amount.
“There are locations everywhere – Great Britain, Europe, Japan – that had shifts in their means after considering the change points. Although the cause is still unknown, it appears that some are natural shifts and some are human-caused – we take these change points into account in our analysis and think that it’s something worth looking into for climatologists or oceanographers,” said Lee.
“Many extreme climate events, like extreme precipitation or temperatures, often bring damages that can be recovered. But rises in extreme sea levels often bring damages that are perhaps harder to recover. I wanted to study these changes and be at least a small part of the efforts taken against them,” Lee continued.
Lee will be finishing his PhD in summer 2022.