Long and very intense droughts are reducing grasslands and shrublands' role as sinks, just when these ecosystems are crucial for climate balance. A new study published in the journal Science finds that the combination of drought duration and intensity greatly exacerbates losses in plant productivity, the basis of carbon capture through photosynthesis.
With presence in almost half of the planet's surface and safeguarding more than 30% of the Earth's carbon, these natural systems are a key piece. The study shows that after Four years of extreme drought, the average loss of productivity doubles compared to moderate situations, weakening the carbon storage capacity of grasslands and shrublands.
A global study and its scope
The research, led by Timothy Ohlert and Melinda D. Smith (Colorado State University), has brought together 120 institutions from around the world to put numbers to a growing problem. Experimental data have been analyzed 74 ecosystems distributed across six continents, providing a robust and comparable overview of the impact of drought on different biomes.
The work is part of the International Drought Experiment (IDE), the largest experimental network dedicated to drought, with more than 170 specialists collaborating. The design is consistent across sites: structures that reduce rainfall by a controlled amount allow for measuring how vegetation responds when rainfall is sustained and extremely scarce.
Thanks to this common methodology, the conclusions are widely extrapolated: The intensity and duration of the drought act synergistically, increasing productivity losses much more than if only one of the factors were considered separately.
Most exposed regions and why
The results point to the arid and semi-arid zones The most vulnerable regions: the Mediterranean, the southwestern United States, southern Africa, and Central Asia experience the most severe impacts. In these areas, reduced water availability, combined with high temperatures and high radiation, triggers evaporation and complicates the regeneration of vegetation cover.
Prolonged drought interferes with critical moments in the life cycle of plants—emergence, growth, and reproduction—causing sharp declines in productivity. Although wetter grasslands and shrublands (e.g., northern Europe or north-central USA) are more resilient to moderate episodes, chaining Extreme droughts over several years erode their resilience, with setbacks that can reach up to 160% compared to less severe conditions.
In addition, episodes that were previously considered extraordinary or “centennial” They tend to become more frequent and longer-lasting with global warming, the authors warn. The result is a greater risk of cumulative losses where water is already the limiting factor.
Consequences for carbon, livestock and agriculture
As primary productivity falls, carbon input into the systems is reduced and its sink function is weakened. Repeated extreme droughts, therefore, not only reduce annual biomass but also compromise climate-related ecosystem services on a global scale.
The implications go beyond the ecological sphere: the Livestock farming depends on pastures and agriculture benefits from the erosion protection these habitats provide. Grasslands and shrublands support a key biodiversity—pollinators and microorganisms— which promotes soil fertility and crop productivity.
If extremes are repeated, management costs increase, damage from soil loss worsens, and the stability of agricultural and livestock systems decreases. Overall, a persistent decline in productivity It undermines both CO2 capture and food security.
The role of Spanish science and long-term data
El IICG-URJC It has been sampling scrublands and annual grasslands in the southeast of the Community of Madrid (El Espartal facility, Ciempozuelos) for nearly a decade. These long series demonstrate that maintain experiments over time It is essential to capture cumulative effects and interannual variations.
At the IPE-CSIC, the data from subalpine pastures in the Aragonese Pyrenees reflect more attenuated impacts than in arid areas, which highlights the regional heterogeneity of responsesOverall, the international coordination of the IDE—with common protocols—makes it easier to compare sites and scale results with greater confidence.
The picture drawn by the research is clear: when the drought is intense and prolonged, grasslands and scrublands lose muscle And their carbon storage capacity is suffering, especially in already dry regions; understanding these dynamics with comparable, long-term data will be vital to guiding management and adaptation in a more changing climate.
