Real space The laser is currently cruising 300 miles above your head. Launched in 2018, NASA’s ICESat-2 satellite features a lidar instrument, the same type of technology that allows self-driving cars to see in three dimensions by spraying lasers around them as they roll down the street and analyzing reflected light. But instead of mapping the road, ICESat-2 measures the altitude of the Earth’s surface extremely highly accurately.
While this space laser means you’re not harming you, it does hints at a catastrophe. Today in the magazine Nature Communications, scientists describe how they used the new ICESat-2 lidar data to map planets on land that are less than 2 meters above sea level, making it vulnerable to sea level creep. Combining these data with population data, they calculated that currently 267 million people live in these risk areas. Assuming sea levels rise by one meter by 2100, they predict that 410 million people will finally live in the affected zone. Asian countries like Bangladesh and Indonesia are particularly vulnerable, but the United States and Europe will also not lack at-risk populations.
“We firmly believe that if the world is able to cope with rising sea levels and conserve nature in coastal areas – this is an important aspect – the elevation must be known,” said lead author Aljosja Hooijer, a flood risk expert at the National University. in Singapore and Deltares, a research institute in the Netherlands.
Newspaper estimates, Hooijer points out, are conservative on many levels. They did it first without taking into account the explosive population growth in the world’s cities, due to the uncertainties involved in calculating where people will finally move. Currently 55 percent of the planet’s population lives in urban areas, which United Nations projects it will rise to 68 percent by 2050. But it will not go smoothly – the population of certain cities may grow faster than others or even decline.
“The work fills a very large void we have at the moment,” says Arizona State University geophysicist Manoochehr Shirzaei, who studies rising sea levels but was not included in this new study. Scientists are doing well models sea level rise, Shirzaei adds, “but when you want to quantify the risk of flooding, you have to know the altitude as well. And that is a great unknown. ”
Earlier, researchers used satellite radar to map altitudes. It works on the same principle as the lidar, only it repels ground radar instead of lasers. “The problem with radar is that it can’t penetrate vegetation – just a little bit,” says Hooijer. “It’s stuck somewhere between the canopy and the ground surface, and the measuring height you get is somewhere in between.” Lasers, on the other hand, easily penetrate the vegetation, which gives a more accurate measurement. (You may have heard of scientists using lidar to peek through the trees of the Amazon jungle and map of ancient ruins hidden below.)
Hooijer found that 72 percent of the population at risk of flooding would live in the tropics. Tropical Asia alone accounts for 59 percent of the risk area, as the region is particularly low. “It’s a huge problem for developed countries – for Europe and countries,” says Hooijer. “But if you look at the road map, who are the people who will suffer the most, and probably soon?” These are poor people, mostly living in underdeveloped areas. Not so much attention is paid, that this is a really hot place. We ourselves were surprised by the numbers. ”
There is another problem: in addition to dealing with seawater that invades their shores, some cities are sinking. Land reclamation is a phenomenon in which ground compact, usually due to excessive groundwater abstraction. Coastal towns are particularly prone to subsidence due to their geology, as urban centers have in the past popped up where rivers meet the sea. Over the millennia, the river would settle layer by layer of clay, and the city would grow on it. But as the metropolis taps into the base aquifer, this clay decays like an empty water bottle and the city can go along with it. The more the urban center grows, the more people need hydration, which increases the rate and severity of subsidence.
Hooyer’s modeling takes settlement into account, but uses a unique rate of height loss – half a centimeter per year – worldwide, instead of calculating the rate for each coastline independently. That would not be feasible. However, researchers know that some areas are deteriorating much faster than that: for example, in parts of Jakarta, the country is sinking to 10 inches per year. By 2050, 95 percent of northern Jakarta could be under water because the mainland is elevated is decreasing while the sea level increases. The problem is so bad that Indonesia plans to move its capital out of the city.