Lake Baikal is recovering after decades of decline, according to a study in Geophysical Research Letters. Researchers analyzed tree rings from the past 343 years to track water levels. Since 2017, the lake got a 145% increase in streamflow. These signs showed that the environment is finally starting to heal.
Lake Baikal in Siberia holds around 20% of the world's surface freshwater, making it the most voluminous freshwater lake (Lake Superior on the United States–Canada border is the largest by surface area). This makes the lake one of the most important environments for biodiversity—in fact, it was designated a UNESCO World Heritage site in 1996 because of this. Yet it has shown considerable decline over the last century, with aridification spreading across East Asia.
As the lake has dried out, there have been increasing concerns over water security for the local environment, as well as the human populations who rely on it for drinking water, agriculture and hydroelectric power. However, a new study published in Geophysical Research Letters offers hope that the pattern may be starting to change.
Tides of change
Doctoral researcher Shijie Wang, of Yunnan University, and colleagues turned to trees to help them understand the transformation. Trees growing near to a lake environment can be used as an indicator of how lake levels have fluctuated over time. The science, known as dendrochronology, uses the rings in tree trunks as the clue: wider rings indicate wet or warm years while narrower rings suggest there was drought, cold or severe stress.
The scientists took small cores from the trunks of pine trees surrounding the lake, as well as using information stored in the International Tree-Ring Data Bank. By analyzing tree rings in the area from the past 343 years, the team reconstructed reduced flow from the Selenga River into the lake throughout the 20th century. They found that streamflow was reduced by up to 90% in the most severe periods, with approximately half of the years with extreme drought occurring since 1900.
But since 2017, that trend has reversed, flipping to a 145% increase in streamflow above the long-term average. Other signs of improvement in the landscape include rising lake levels and enhanced vegetation growth. Such periods of increased streamflow tend to be abrupt and short, whereas hydrological decline tends to be gradual but persistent.
Climatic cold blobs
The researchers say these changes in streamflow are not affected by local land temperature or potential evaporation (the amount of water that could evaporate from plants or the ground); instead, they are strongly linked to measures of moisture, like precipitation, drought severity, soil wetness, snowmelt and the balance of water supply and demand in the river basin.
There is also a correlation with lower sea surface temperatures and higher sea ice cover in the neighboring North Pacific and Arctic oceans leading to increased streamflow.
They suggest changing weather patterns are the main factor driving this regeneration of Lake Baikal, with increased moisture coming from the Nordic and Siberian shelf seas. This may also be supported by a slowdown in regional Arctic warming, which has led to reduced sea ice loss in the Bering, Chukchi and Okhotsk seas. However, the researchers are keen to stress this change in Arctic warming is due to natural climate variability rather than a significant shift in global warming.
This is not an isolated occurrence either, as a similar "cold blob" has formed in the North Atlantic, where an area of 2.5 million square kilometers (965,000 square miles) south of Greenland has cooled by up to 1°C over the last century, against the background warming seen across Earth's oceans.
Planning for the future
The study highlights the importance of understanding how hydrological systems continue to change as they impact projections of lake levels and regional aridification. With dry spells becoming more prolonged and wet events more intense, being adaptable to water resource changes and having appropriate systems in place to safeguard water security are becoming increasingly vital.
This can include improving water storage facilities to save water for domestic and agricultural use during dry periods, identifying rocks underground that "recharge" during rain events and from which water can be safely extracted (known as aquifers), as well as improving wastewater infrastructure so sewage systems are not overloaded. Additionally, restoration of the Selenge River Delta wetlands would boost ecological benefits as they can store water for lengthy periods and slowly release it during drier months.
By understanding the nuance of changing weather patterns and their impacts on the local environment, scientists can better prepare for a more sustainable future.