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Middle Volga Experienced Half as Many Droughts in 20th and 21st Centuries as in 19th Century
ISTOCK
These were the findings made by researchers of the HSE Faculty of Geography and Geoinformation Technology and the Russian Academy of Sciences Institute of Geography. They studied tree rings of Scots pines for an insight into the region's climatic past and published their results in Dendrochronologia.
Several factors influence tree ring width, such as the area’s physical geography, natural biochemical cycles, and the genetic makeup of the species. In the Northern Hemisphere, the ring width of Scots pines (Pinus sylvestris) is shaped mainly by temperatures for trees growing in the north and mainly by moisture for those growing in the south.
The Middle Volga is located in a moderate climatic belt, making it more difficult to determine which of the factors is more important for tree ring width. However, researchers of the RAS Institute of Geography and the HSE Faculty of Geography and Geoinformation Technology have been able to trace back the climatic variations in the region over the centuries.
The scientists examined 16 Scots pine tree ring width chronologies, ie annual tree-ring circular growth data, from different locations across the Middle Volga, from boreal forests in the north to mixed forests in the centre, to forest-steppes in the south. For each chronology, they correlated the tree ring width with the known historical data on temperatures, precipitation and drought severity indices in the region for the current and previous years.
Tree width ring chronologies were found to be more sensitive to all of the above climatic factors in pines growing on the region's southern border in taxing climate conditions for coniferous species, as opposed to the central and northern parts of the Middle Volga providing a more favourable environment for pines.
Having determined the correlation between tree ring width and climatic factors, the researchers were able to trace back the region's climate using the method of dendrochronology. They examined the tree ring width parameters for years with missing weather data and used the measurements to build a complete timeline, thus reconstructing the Middle Volga's climatic history between 1830 and 2014.
There were more drought years in the 19th century compared to the 20th and 21st centuries (14 versus 7 and 1, respectively), but droughts were more severe in the 20th and 21st centuries. It was also found that droughts occurring early in summer were critical for tree ring growth.
The tree ring method makes it possible to complement observation data and to estimate climatic conditions with one-year accuracy. The patterns of wide or narrow rings record the year-to-year fluctuations in tree growth. By comparing tree ring width with local weather records such as temperature, we find correlations between these values for each year. We have thus reconstructed almost two centuries' worth of drought data for the region. Similar reconstructions from other regions can help track global climate change.
Our colleagues have worked in the Middle Volga before, but they used dendrochronological methods for other research objectives. This study is part of our long-term effort to reconstruct the Russian Plain's climatic history. We have surveyed a 500 by 500 kilometre-area in six regions of the Middle Volga. The Dendrochronology Laboratory of the RAS Institute of Geography stores wood samples from architectural elements of buildings; therefore, we can hope to extend our reconstruction further into earlier centuries and expand our knowledge of climate change in the region.
Olga Solomina
Academic Supervisor, HSE Faculty of Geography and Geoinformation Technology
IQ
Veronika Kuznetsova
Research Fellow, RAS Institute of Geography