The water levels of the Caspian Sea fell by around ~5 feet (~1.5 meters) during the years 1996 through 2015 — or, to be more accurate, by an average of around 7 centimeters (3 inches) a year — according to a new study published in Geophysical Research Letters.
The cause of this rapid drop in water levels, according to the research, was mostly rising temperatures and increasing evaporation, accompanying intensifying climatic changes.
As it stands, current Caspian Sea water levels are now only around 1 meter (3 feet) above the historic low level the sea reached in the late 1970s — despite the fact that water levels there rose by around 12 centimeters (5 inches) per year between 1979 and 1995.
In other words, the rapid gain of the first few decades after the 1970s low has been more or less wiped out. With temperatures slated to continue rising for the foreseeable future, this means that the long-term fate of the Caspian Sea is looking bleak.
“From our point of view as geoscientists, it’s an interesting place because it’s possible to construct a sort of budget for the total amount of water that’s there,” commented Clark Wilson, a geophysicist with the Jackson School of Geosciences at the University of Texas at Austin, and co-author of the new study. “The real control that causes it to go up and down over long periods of time is really most likely the evaporation, which is almost completely dominated by temperature.”
The press release provides more: “According to the data from the study, the average yearly surface temperature over the Caspian Sea rose by about 1° Celsius (1.8° Fahrenheit) between the two timeframes studied, 1979-1995 and 1996-2015. These rising temperatures are likely a result of climate change, according to the study’s authors.”
“The Caspian Sea, located between Europe and Asia, is roughly the size of Montana at 371,000 square kilometers (143,244 square miles). It has experienced substantial changes in its water level over the past several hundred years, but previous studies were unable to nail down the exact causes of the sea level changes. The Caspian Sea is bordered by five countries and contains an abundance of natural resources and diverse wildlife. The sea also contains oil and natural gas reserves, and is an important resource for fisheries in the surrounding countries.”
The research is apparently the first to provide “convincing” evidence that evaporation rates over the Caspian Sea are a more important driver of water level changes there than river discharge rates or rainfall — at least according to CNES space geodesist at the Laboratoire d’Etudes en Géophysique et Océanographie Spatiales (LEGOS) at Observatoire Midi-Pyrénées in Toulouse, France, Anny Cazenave. Cazenave was not involved in the study.
“An interesting finding from the study is that over the last two decades, climate-model predicted water loss … apparently cannot be balanced by water gain from discharge, and increased evaporation is a major factor leading to this imbalance,” Cazenave noted. “If the temperature in the Caspian Sea region continues to increase, the evaporation rate is also expected to increase. Unless river discharge increases accordingly or precipitation in the Caspian drainage basin increases accordingly, the imbalance is likely to continue.”
The press release provides some more information: “Evaporation will have the biggest impact on the northern portion of the Caspian Sea because much of the water in that area is less than 5 meters (16 feet) deep, Wilson said. If the current trend of a 7-centimeter decrease per year continues at a steady rate, it would take around 75 years for the northern part of the sea to disappear, according to the new study.
“The Caspian Sea supports many unique and ancient species remaining from when the sea was a part of the Tethys Ocean during the Mesozoic era, approximately 300 million years ago. Although most of these species live in the southern and middle regions of the Caspian, some use the shallow northern area as spawning grounds, including 90 percent of the world’s sturgeons. Dropping sea levels would also impact the Kara-Bogaz-Gol Bay on the eastern side of the sea, which is less than 5 meters (16 feet) deep and contains one of the world’s largest natural deposit of sea salts, according to the study’s authors.”
All of that said, it’s not completely clear yet how things will play out with regard to water levels, river discharge rates, and rainfall levels. It’s a complex situation, but it’s one that could change to an incredible degree over just a century or so’s time. Most regional inhabitants are probably unaware of what may now be in the works thanks to rising temperatures and climate change.
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