A sweeping global study has revealed that multi-year, extreme droughts—akin to the conditions that created the 1930s Dust Bowl—inflict far more severe and escalating damage on the world’s grasslands and shrublands than previously understood. The research found that after four consecutive years of intense drought, the loss of plant productivity more than doubled compared to losses from moderate droughts, signaling a critical decline in the health of ecosystems that cover nearly half of the planet’s land surface.
These findings, published in the journal Science, raise urgent concerns for global food security and climate stability. Grasslands and shrublands are essential for sequestering carbon, supporting biodiversity, and providing forage for the world’s livestock. A Colorado State University-led research team discovered that the combination of drought intensity and duration creates a compounding effect, progressively weakening the ability of these vital ecosystems to recover. With climate change projected to increase the frequency of such severe, prolonged droughts, the study suggests many regions could face unprecedented ecological degradation and productivity losses.
A Global Experiment Simulating Extreme Weather
To understand the escalating impacts of sustained water scarcity, scientists initiated the International Drought Experiment, a coordinated effort involving more than 170 researchers at sites across six continents. The project was specifically designed to investigate the interaction between the severity of a drought and its duration, a combination that has been difficult to study systematically. The experiment’s novelty lies in its scale and its method for mimicking worst-case climate scenarios.
At various grassland and shrubland locations, researchers constructed rainfall manipulation structures capable of reducing the amount of water received by the ecosystem during each rainfall event. For four consecutive years, these structures were used to simulate a 1-in-100-year drought event, allowing the team to measure the cumulative stress on plant life year after year. This long-term, globally coordinated approach provided a rare and comprehensive look at how ecosystems respond when extreme conditions are not just a temporary shock but a persistent reality.
Compounding Losses Reveal a Tipping Point
The central conclusion of the four-year experiment is that prolonged, extreme drought pushes ecosystems past a critical threshold, leading to accelerating declines in function. The damage inflicted in the third and fourth years of simulated drought was significantly greater than in the first two, demonstrating that the land’s resilience wears away over time.
Quantifying the Productivity Collapse
The study measured primary productivity, which is the creation of new plant biomass through photosynthesis. This metric is a fundamental indicator of an ecosystem’s health and its ability to support life. Researchers found that after four years of extreme drought, the loss in plant productivity was more than twice as severe as the losses recorded in sites experiencing moderate drought conditions over the same period. This nonlinear response shows that the effects of drought are not steady or predictable but can intensify dramatically as the stress continues.
The Peril of Persistence
According to the researchers, the duration of a drought is a powerful amplifier of its intensity. A single year of extreme dryness, or even several years of moderate dryness, does not have the same destructive effect as consecutive years of severe water shortage. This persistence is what exhausts the ecosystem’s coping mechanisms, such as stored soil moisture or the resilience of drought-tolerant plant species. Once these buffers are gone, the system begins to collapse, leading to irreversible damage like widespread plant death and soil loss.
Echoes of the American Dust Bowl
The research draws a direct parallel between the experimental findings and the historical catastrophe of the American Dust Bowl. That nine-year environmental disaster was not caused by a single dry year but by a succession of extremely dry years that magnified the impact on the Great Plains.
A Historical Warning Sign
Melinda Smith, the CSU biology professor who led the study, noted that the most severe effects of the Dust Bowl, including the immense dust storms and catastrophic soil erosion, only emerged after several consecutive years of intense drought. The new data provides a scientific explanation for this historical observation, showing how persistent dryness leads to a breakdown of the grassland ecosystem. The study confirms that it is the unrelenting nature of extreme drought that triggers the most devastating consequences.
Future Climate Projections
The findings are particularly alarming in the context of modern climate change. Climate models predict that Dust Bowl-type droughts are likely to become more frequent and widespread in the coming decades. Regions that are already arid or semi-arid, which depend heavily on fragile grassland ecosystems, are especially vulnerable. The research suggests these drylands could experience dramatic declines in productivity, threatening the livelihoods of millions of people who depend on them.
Implications for a Warming Planet
The accelerated loss of productivity in the world’s grasslands and shrublands has profound consequences that extend beyond the boundaries of these ecosystems. The impacts threaten to disrupt global food systems and could create a dangerous feedback loop that exacerbates climate change itself.
Threats to Global Food and Agriculture
Grasslands are the foundation of the world’s livestock industry, providing the primary source of forage for cattle, sheep, and other grazing animals. A sharp decline in the productivity of these lands means less available food, which could lead to reduced agricultural output, economic instability for ranchers and pastoral communities, and increased pressure on global food supplies. Ecosystem degradation on this scale poses a significant challenge to sustaining food production in a world with a growing population.
A Weakened Carbon Sink
Beyond their agricultural importance, grasslands and shrublands are critical components of the global carbon cycle. Together, they absorb and store a significant amount of carbon dioxide from the atmosphere. When their productivity declines, so does their ability to sequester carbon. Widespread degradation could weaken this vital carbon sink, leaving more CO2 in the atmosphere and potentially accelerating the pace of global warming. This creates the risk of a cycle where climate change drives more extreme droughts, which in turn further weaken ecosystems and their ability to mitigate climate change.
