Analyses of up to 9,000-year-old wood from the Alps reveal a long-term summer drying trend throughout the Holocene epoch. The study, conducted by researchers at the University of Innsbruck and published in Science Advances on April 4, 2025, suggests that recent droughts, while intense, are not unique within the context of Holocene variability.
The research team, led by dendrochronologist Kurt Nicolussi, analyzed stable oxygen isotopes (δ18O) in tree rings from 192 larch and stone pine trees. These isotopes act as indicators of seasonal climate conditions, reflecting evaporation rates during tree growth. Higher δ18O values indicate greater evaporation and drier conditions.
The study found that the early to mid-Holocene (approximately 9,000 to 5,000 years ago) was characterized by relatively moist summers. A drying trend has been observed since 5,000 to 4,500 years ago, punctuated by distinct wet and dry phases. Notably, the Little Ice Age (c. 1260-1860 AD), often described as cool and wet, also contained periods of significant drought.
"Current drought periods may seem extraordinary in their intensity, but they are not unique in the context of Holocene variability," the study states. This finding has significant implications for understanding and managing water resources in the Alpine region, which is highly vulnerable to the impacts of climate change. The detailed chronological data provided by tree-ring analysis offers a valuable tool for assessing long-term hydroclimatic changes and informing future climate models.
The research team plans to further analyze hydrogen and carbon isotopes within the tree rings, as well as the cellulose content of the wood, to gain a more comprehensive understanding of past climate conditions. The combination of dendrochronological isotope data with other proxy data and climate models holds great potential for future studies on the dynamics of the Central European water balance.