Extreme Droughts Weaken Ecosystems - BFH-HAFL Conducts Research

Droughts are among the most severe disturbances in ecosystems. Multi-year periods of dryness cause enormous damage, both ecologically and economically. With climate change, extreme droughts are expected to occur more frequently, prompting researchers around the world to learn more about their consequences. In a study now published in Science, they analysed data from 74 grass and shrub landscapes on six continents. The big question: Do ecosystems adapt to prolonged drought—stabilising their function—or do they become increasingly weakened over time? Until now, scientific answers had been unclear. The basis was the international "Drought Experiment" (IDE), a multi-year global study on the effects of dryness on plant production, which indicates the performance of ecosystems. The School of Agricultural, Forest and Food Sciences BFH-HAFL is the only Swiss institution that contributed data to this study.

The results are generally clear: The longer and more intense the droughts last, the more the ecosystems suffer from them. However, it also shows, "Many habitats can adapt to multi-year dry periods after initial productivity losses," says Andreas Stampfli from BFH-HAFL. It is remarkable that some of the studied sites showed hardly any changes in their productivity even after several consecutive drought years. Stampfli states, "These are less water-limited ecosystems, such as those found in the more humid climates of Switzerland and Central Europe. These apparently react overall less sensitively, because even with extreme precipitation shortages, water remains in the soil, allowing species communities to adapt." The situation is different in typically dry grassland areas of the USA, China, Argentina, or Australia.

The study further shows that when extreme dry years, which normally occur only once in a hundred years, happen consecutively for several years, plant production collapses dramatically. After four such years, productivity decreases by about 160 percent more than during moderate droughts.

Worldwide Drought Experiment Examines Consequences for Grass and Shrublands

The researchers used special rain shelter constructions to simulate year-round droughts over three to four years in order to measure their impact on ecosystem productivity. Besides duration, the intensity of such events was also considered. Each site underwent a "1-in-100-year drought"—an extreme situation that is rare today but is expected to become much more frequent due to climate change.

Ecologist Andreas Stampfli and ecologist Michaela Zeiter from BFH-HAFL contributed data from their experiment in Thun. Andreas Stampfli explains, "Six of twelve equally sized meadow plots were covered with Plexiglas slats, reducing rain contact by 33 percent compared to normal." This simulates exactly the driest year of the last hundred years with an average annual rainfall. Before, during, and after the simulated drought, the function and species composition of the ecosystem were recorded.

Together with the authors of the study, Andreas Stampfli and Michaela Zeiter warn, "If droughts become longer and more severe in the future, ecosystems could lose their resilience. This is a warning signal for the future of many habitats."

Publication Note: Timothy Ohlert, Melinda D. Smith et al. (2025) Drought intensity and duration interact to magnify losses in primary productivity. Science. DOI: 10.1126/science.ads8144 Legend: Rain shelter construction used from 2016-2019 in the nationally significant dry grassland on the Thun Allmend after light snowfall in early March.
Contact for Media Inquiries
Dr. Andreas Stampfli
andreas.stampfli@bfh.ch
+41 31 910 21 98
Dr. Michaela Zeiter
michaela.zeiter@bfh.ch
+41 31 910 22 42

Editor's note: Image rights belong to the respective publisher.