Vienna (OTS) – An international research team with BOKU participation uses extensive tree ring analyzes to prove that the atmosphere in Europe has become significantly drier in the last few decades due to greenhouse gas emissions compared to pre-industrial times. This exacerbates droughts, increases the risk of forest fires and is risky for forests and agriculture. The study has just been published in the current issue of NATURE Geoscience.
A measure of air dryness is the vapor pressure deficit (VPD for short). This physical quantity describes the difference between the actual and the maximum possible water content of the air, so to speak the “thirst for water” of the air. Water-thirsty air with a high VPD draws more water from the soil and plants, the growth of trees is reduced and trees can even die. The dried out vegetation and dry soils increase the risk of forest fires. It is known that the VPD increases in a warming climate. However, little was known about the spatial extent and long-term fluctuations until pre-industrial times without human influence.
Oxygen isotopes in tree rings report on the past climate
An international team of 67 researchers led by Kerstin Treydte from the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) collected oxygen isotope data based on two EU projects (ISONET, MILLENIUM) and a Swiss collaborative project (iTree). in tree rings from all over Europe. Michael Grabner and Rupert Wimmer from the Institute for Wood Technology and Renewable Resources at BOKU sampled different tree species from the Lainzer Tiergarten, Vienna Basin and Dachstein. Isotopes are different atomic variants of the same element, such as oxygen. Water contains lighter and heavier versions of oxygen atoms. Trees absorb water primarily through their roots and release some of it back into the air through their leaves. The remaining part of the water plays an important role in building new wood cells. The ratio of light and heavy isotopes changes during soil evaporation, leaf evaporation, and wood formation. It is precisely these changes that are largely controlled by the VPD. This means that tree rings can provide information about past and present air dryness. With this method, changes in the VPD over 400 years have now been reconstructed for the first time on a large scale throughout Europe.
Man-made and strongest in Central Europe
Using additional model simulations, the research team was able to independently test the findings from the tree ring data. The models also come to the conclusion that air dryness in the 21st century is exceptionally high compared to pre-industrial times! Furthermore, they show that today’s VPD values could not have been achieved without greenhouse gas emissions. So the human influence is obvious.
“VPD is particularly important for agriculture because the higher it is, the greater the water requirements of crops. More irrigation is necessary and yields decrease. In forests, wood supply and carbon sequestration are at risk, leading to uncertainties regarding climate regulation and the future carbon storage of these ecosystems,” says Rupert Wimmer. “These effects on agriculture and forestry could particularly affect Austria.” This is particularly worrying in the densely populated regions of Europe and shows the urgency of reducing emissions and the importance of adapting to climate change. The study findings are intended to help refine simulations of future climate scenarios and assess the potential threat posed by high VPD to ecosystems, the economy and society.
The DOI number for the article in NATURE Geoscience is 10.1038/s41561-023-01335-8. The article is below this URL available.
Questions & Contact:
Mag. Astrid Kleber-Klinger
University of Natural Resources and Life Sciences Vienna
Head of public relations
Email: astrid.kleber@boku.ac.at
Tel.: 0664 8858 6533