September 15, 2022 - The Shrinking Coastline of the Caspian Sea

The Shrinking Coastline of the Caspian Sea
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Measured by surface area, the Caspian Sea is the Earth’s largest inland
water body, spanning about 143,200 square miles (371,000 square
kilometers). Measured by economic, social, and biodiversity standards,
it is priceless. The Caspian contains a rich oil and gas reserve, an
important fishery, resources for agriculture, provides for recreation
and work for large population living nearby, and contains many
important and sensitive species—for example, it contains an estimated
90 percent of the last sturgeon left in the world.

Every square inch of the Caspian Sea holds ecological treasure, but the
northern section holds a particularly important and sensitive
ecosystem. Here, the shallow waters teem with mollusks, crustaceans,
fish, and birds. Seals raise their pups on winter ice that usually only
forms in this part of the lake. All rely on a healthy water level for
their existence. However, the Caspian Sea is rapidly shrinking.

Radar altimetry data collected by multiple satellites and compiled by
NASA's Global Water Monitor indicate that the Caspian's water levels
have been dropping since the mid-1990s. As climate change causes
increased air temperature, evaporation will increase—and will be a
primary driver of loss of water from the Caspian Sea. In a paper
published in 2019, it was estimated that Caspian water levels could
drop by 9 to 18 meters (30 to 59 feet) by the end of the 21st century,
enough that it would lose about a quarter of its area and uncover about
93,000 square kilometers (36,000 square miles) of dry land. That is an
area about as large as Portugal.

In a newer paper, published in 2021, scientists ran several different
models to estimate water loss in the Caspian Sea due to climate change,
which gave estimates of loss by the year 2100 as low as 8 meters (36
ft) and as high as 30 meters (98 ft). Because extraction (human use or
diversion of water) is also an important driver of water loss in the
Caspian, the scientists also estimated this factor—something overlooked
in most other estimates. They found that water extraction would add up
to 7 meters (23 feet) further loss. While the deepest parts of the
Caspian plunge to more than 1,000 meters below sea level, the northern
portion has an average depth of only 5-6 meters. All but one of the
models in this study showed complete desiccation of the northern
section of the Caspian by the end of the 21st century.

On September 6, 2022, the Moderate Resolution Imaging Spectroradiometer
(MODIS) on the Terra satellite acquired a true-color image of the
northeastern section of the Caspian Sea. The sprawling, green Volga
River Delta can be seen along the northern coast at the left (west)
edge of the image. Swirls of green and tan color the shallow water,
created by the sediment carried in by the fresh water of the Volga and
by currents that stir up sediment from the shallow sea floor in this
region. A broad area of the coastlines near the waters are tinted light
gray. In addition, patches of bright white along with a large swath of
white color the landscape southeast of the Caspian. These light colors
are salt and other minerals left behind after evaporation.

For our Image of the Day, we have compared the September 6, 2022 image
with a true-color image acquired by the MODIS instrument on Terra on
September 20, 2006. In this image, there is no light-colored,
salt-laden halo along the northern shore and only a relatively small
“salt-shadow” in the east and south. Water fills the serpentine area
that, twelve years later, has become a thick mineral crust.

While this Image of the Day gives a striking comparison illustrating
the shrinking shoreline of the Caspian Sea, it is even easier to
visualize the change with a roll-over comparison. Thanks to the NASA
Worldview App, this can be easily visualized simply by clicking
here. Using the measurement tool in the lower left corner of the
roll-over comparison on Worldview, it appears that the eastern
coastline has receded approximately 17.5 feet (5.3 meters) in the last
twelve years.

Image Facts
Satellite: Terra
Date Acquired: 9/11/2022
Resolutions: 1km (319.8 KB), 500m (788.6 KB), 250m (513.9
KB)
Bands Used: 1,4,3
Image Credit: MODIS Land Rapid Response Team, NASA GSFC



https://modis.gsfc.nasa.gov/gallery/individual.php?db_date=2022-09-15

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