Real space The laser is now cruising 300 miles above your head. NASA’s ICESat-2 satellite was launched in 2018 and is equipped with lidar instruments. This technology allows self-driving cars to achieve a three-dimensional view by jetting laser light around themselves while driving on the street and analyzing the reflected light. However, ICESat-2 is not a road map, but an extremely accurate measurement of the height of the earth’s surface.
Although this space laser means you have no harm, but it does Herald disaster. Today in the magazine Nature Communications, scientists description How do they use ICESat-2’s new lidar data to map the earth’s land at an altitude of less than 2 meters, which makes it vulnerable to rising sea levels. Combining these data with population figures, they calculated that 267 million people currently live in these high-risk areas. Assuming that the sea level rises by 1 meter by 2100, they predict that 410 million people will eventually live in the affected areas. Asian countries such as Bangladesh and Indonesia are particularly vulnerable, but there are also high-risk groups in the United States and Europe.
“We firmly believe that if the world can cope with rising sea levels and protect the nature of coastal areas-which is an important aspect-elevation must be known,” said Aljosja Hooijer, the main author of the study and a flood risk expert. The National University of Singapore and the Dutch research institute Deltares.
Hooijer emphasized that the paper’s estimates are conservative on many levels.On the one hand, they did No Consider the explosive growth of the world’s urban population because of uncertainty when calculating where people will eventually move.Currently, 55% of the earth’s population lives in urban areas, of which United Nations Project It will rise to 68% by 2050. But this will not develop in a balanced way-the population growth rate of some cities may be faster than others, or even decline.
“This work fills a very large gap we currently have,” said Manoochehr Shirzaei, a geophysicist at Arizona State University. Study sea level rise But did not participate in this new research.Scientists are good Model Sea levels are rising, Shirzaei added, “But when you want to quantify flood risk, you also need to know the altitude. This is a big unknown.”
In the past, researchers used satellite radar to draw elevation maps. It works on the same principle as lidar, except that it reflects radar instead of laser light from the ground. “The problem with radar is that it can’t penetrate vegetation-it can only penetrate a little,” Hooijer said. “It’s stuck somewhere between the tree canopy and the soil surface, and the elevation measurement you get is somewhere in between.” On the other hand, the laser can easily penetrate vegetation and provide more accurate measurements. (You may have heard how scientists use lidar to see through the trees and Map ancient ruins Hidden below. )
Hooijer found that 72% of the population at risk of flooding will live in the tropics. Tropical Asia alone accounts for 59% of the risk area, because the region is particularly low-lying. “For developed countries-for Europe and the United States, this is a huge problem,” Hooijer said. “But if you look at the road map, who will suffer the most, and possibly the fastest? These are poor people, mostly living in underdeveloped areas. Not getting much attention, this is indeed a hot spot. We are surprised by these numbers ourselves. .”
There is another problem: In addition to dealing with seawater that erodes the coast, some cities are also sinking.Land subsidence is a phenomenon Ground briquetting, Usually due to Overexploitation of groundwater. Coastal cities are particularly prone to sinking due to geological reasons, because urban centers have always appeared where rivers and seas meet. For thousands of years, a river will deposit layers of clay, and cities will grow on it. But as the metropolis enters the lower aquifer, this clay collapses like an empty water bottle, and the city can go with it. The more urban centers develop, the more people need to be hydrated, which will increase the speed and severity of sinking.
Hooijer’s model does take into account subsidence, but it uses a uniform rate of descent in elevation around the world-half a centimeter per year-rather than calculating the rate of descent for each coastline individually. That is impossible.Nevertheless, researchers know that some areas are sinking much faster than this: For example, in parts of Jakarta, the land sinks as much as 10 inches per yearBy 2050, 95% of northern Jakarta may be submerged due to the altitude of this land Is decreasing While the sea level is rising. The problem is so serious that Indonesia is planning to move its capital out of the city.