Enlarge image
When Dorsoidong Co Lake was still light blue: Satellite image from 1987
Photo: Joshua Stevens / NASA Earth Observatory
We mostly know problems with melting ice, rising temperatures and meltwater runoff from the polar regions of the earth - the Arctic in the north and the Antarctic in the south.
But they also exist in a region that glaciologists sometimes refer to as the third pole: What is meant is the Tibetan Plateau, the highest plateau in the world.
Here, too, glaciers store gigantic amounts of fresh water - there are tens of thousands of these sometimes larger, sometimes smaller ice tongues between the numerous, rugged mountain ranges.
In total, the region covers more than two million square kilometers, which is roughly the size of Greenland.
How much some of these glaciers have changed in recent years can be seen in the two lakes in the pictures below in a temporal comparison.
The waters are located west of the Tanggula Mountains - a small mountain range in the central part of the Tibetan highlands.
The images show the growth of Chibzhang Co (right in the picture) and Dorsoidong Co. The first picture was taken in October 1987; the second image shows the same area in October 2021. The two lakes have grown larger over time as the mountain glaciers have lost substance and have shrunk. However, NASA, which published the images, points out that part of the enlarged water surface can be traced back to snow. But the images show that the leading edge of the glacier has clearly retreated.
The color difference between Dorsoidong Co Lake from 1987 and the current image is because the two lakes are separated by a narrow strip of land. Its meltwater comes from the glaciers in the mountains in the west, that of Chibzhang Co from the glaciers in the east. In 1987, the Dorsoidong Co likely contained more suspended solids, making the water appear light blue. But in the mid-2000s, the two lakes merged when the rising water level flooded the strip of land.
According to a team of researchers who analyzed decades of images from the "Landsat" earth observation satellites, the area of the lakes grew by 23 percent between 1976 and 2017. The radar height measurements of the satellites also show ever greater depths of the lakes over time. According to data from NASA's Global Water Monitor, the depth of the channel connecting the two lakes increased by about eight meters between the early 1990s and 2021.
Several processes affect the size and depth of the lakes in this area: the annual amount of rainfall, the rate of evaporation, and the amount of runoff from melting glaciers and permafrost during the summer months.
Both lakes are fed by both precipitation and the melting of the glaciers.
On the other hand, some smaller lakes in the southwest, including the Khongnam Tso in the lower left corner of the picture, draw their water from precipitation.
The evaluation and comparison of the satellite data for both types of lakes showed that the water levels in the lakes that are fed by the glaciers are much more stable.
In fact, about half of the total rise in Chibzhang Co and Dorsoidong Co appears to be due to glacial melt.
These two lakes are not the only ones on the Tibetan Plateau that are getting bigger.
In another project, scientists used Landsat data to compare the number and area of lakes on the Tibetan Plateau for 1977 and 2014. They found that the number of lakes had increased by 235.
The area of the lakes had increased by 18 percent.
Another analysis shows that the depth of some of the lakes has also increased - between 2003 and 2018 by an average of 0.3 meters per year.
joe