Evidence of rising seas can be seen along the North Carolina coast.
Storms that are more intense and destructive, floods that spread farther and deeper, and signs of habitat change such as ghost forests are indicators that each year the ocean is just a little higher. .
Sea level rise is an issue that affects coastal communities around the world, and thanks to a new study by Dutch researchers, global vulnerabilities to sea level rise are being mapped in unrelenting detail. previous. Never before has altitude been mapped on a global scale with such precision.
According to the recent study, “Global LiDAR Land Elevation Data Reveal Greatest Sea-Level Rise Vulnerability in the Tropics,” published in Nature Communications, most of this change will occur in the tropics.
This study is the world’s first elevation model to use satellite sensing and telemetry, or LiDAR, data. By taking a holistic approach, the researchers were able to assess which parts of the world are most vulnerable to sea level rise. They classified high vulnerability as the coastal lowlands within 2 meters, or about 6 feet. , above sea level. They found that 62% of these areas are in the tropics, making this region particularly vulnerable to sea level rise. Worldwide, 267 million people live in these vulnerable areas.
According to Dr. Aljosja Hooijer, lead author of the study, these results are conservative. Hooijer used a projection of relative sea level rise of one meter by 2100. Even with such a moderate value, Hooijer found that by 2100, 410 million people could be living in these vulnerable areas.
Although North Carolina is not in the tropics, much of the eastern part of the state is extremely vulnerable to sea level rise. About 47% of the Albemarle-Pamlico peninsula lies less than one meter above sea level, and this region has already seen significant changes due to sea level rise. Coastal forest habitats are being converted to salt tolerant swamps and “ghost” forests, and release sequestered carbon into the atmosphere. Along the rest of the coast, sea level rise poses similar threats of habitat conversion, as well as erosion and flooding.
With quantifiable data, more regions of the world can better plan for rising seas.
“Until there’s really good data on the table, you can’t have a proper discussion about it,” Hooijer said. “But nowadays the data is there and the accuracy is so much higher.”
Hooijer used data from NASA’s ICESat-2, a LiDAR-powered satellite that was launched in 2018. The ICESat-2 measures global land elevation, comparing it to sea level. essentially unprecedented precision, along with a global dataset, both of which allow researchers like Hooijer to ask focused questions about vulnerability to sea level rise around the world. According to Hooijer, this study will be the starting point for many other research questions.
LiDAR generates information about the physical characteristics of the Earth’s surface. It works by emitting laser pulses and timing the time they take to return to the point of origin. The time it takes for the return trip creates an accurate altitude measurement. NASA’s ICESat-2 emits 10,000 laser pulses per second, enabling data in unprecedented detail. These data provide a better understanding of current conditions as well as trends over time.
LiDAR technology has been around in a way since the 1960s. But in recent years it has evolved considerably and is now much more accurate than before. Hooijer was able to use land elevation measurements around the world with a much smaller margin of error.
Previous Global Digital Elevation Models, or GDEMs, relied on satellite radar, which has lower levels of accuracy. Radar at 0.05 degree resolution can only promise results within 0.5 meter accuracy for 19.9% of the measured grounds. In contrast, ICESat-2 LiDAR at 0.05 degree resolution can achieve an accuracy of 0.05 meters for 85.2% of the earth.
One of the notable differences is that the radar often has difficulty discerning vegetation from the ground. LiDAR can penetrate vegetation, allowing more precise measurements of terrain elevation. As GDEMs are often used for flood risk assessments, these data provide a much higher level of confidence in the results.
“It’s mind-boggling this technology,” Hooijer said.
So far, such LiDAR data has only been used at smaller scales, for selected communities around the world. Hooijer’s study is the first global representation of this type of information.
“Now that there is better data, it is almost an obligation for scientists and policy makers to make better assessments which will lead to better planning,” Hooijer said.
In North Carolina, researchers at various institutions and universities are using the latest developments in LiDAR data to ask focused questions about the state’s environmental conditions. North Carolina State University associate researcher Dr. Lindsey Smart used non-satellite LiDAR data for several studies.
In 2020, Smart released a study called “Above-ground carbon loss associated with the spread of ghost forests as sea level rises”. The article used LiDAR data from 2001 to 2014 to map the evolution of coastal landscapes over time. Smart was able to use this data to closely document habitat conversions that lead to loss of above-ground carbon, demonstrating one of the essential ways in which sea-level rise poses a threat to ecosystems. current coastal areas.
Even in just over a decade, Smart has seen the capabilities of LiDAR technology evolve rapidly.
More accurate readings come from a higher laser dot density – in other words, more lasers per area. Between the Smart data used in 2001 compared to 2014, the density of laser points has increased by 18 times.
“The amount of detail you can capture from data like this is amazing,” said Smart. “You have a plethora of research questions you can ask that these rich data sets can answer. “
In recent years, LiDAR data has become more accessible to researchers. Not only is the data available, it can be obtained without imposing a financial burden. According to Smart, the scalable capabilities and accessibility of LiDAR data make it easier for researchers to answer questions about these changing landscapes. This in turn helps states like North Carolina better predict what to expect.
“Organizations or state agencies can be proactive in helping communities adapt or manage future risks,” said Smart. “Some of these questions about where to do this can be answered by looking at LiDAR data and how LiDAR data changes over time. And over time, we get more and more of this data. “