Droughts may be feeding back into processes that are already degrading the planet’s land, much like a forest fire that spreads and accelerates damage. The mechanism involves reducing soil moisture evaporation, which in turn helps sustain dry conditions and can suppress rainfall, promoting further dryness.
The droughts’ reach mirrors the fire’s brutal spread: they propagate through the environment by extending the lack of water across large areas. Recent work highlights that extreme environmental phenomena like droughts can exhibit self-propagating behavior, expanding as water scarcity grows.
Unintentionally caused wildfires and droughts are both unpredictable and challenging to manage once they start. Yet despite being distinct events, they share a common trait: rapid spread under certain conditions that amplify their impact on ecosystems and communities.
Researchers from the European Research Council’s DRY-2-DRY project report that up to 30 percent of the rain deficit may arise from droughts’ self-propagation. A study published in Nature Geoscience and conducted by the Hydroclimatic Extremes Laboratory at Ghent University indicates that reduced evaporation from dry soils can alter the energy balance of the earth’s surface and influence precipitation patterns locally and downwind.
When soil moisture evaporation is limited, atmospheric water supply thins, allowing drought to spread across time and space. The proposed mechanism suggests that drought can persist and broaden its influence even without new moisture input.
The United Nations has warned that extreme weather, global warming, pollution, and drought could arrive as a pressing challenge, described as a looming epidemic by some observers.
Typically, a lack of rainfall shows up as dry soils. Yet precipitation depends on more than rainfall alone; the land surface actively contributes moisture to the atmosphere through evaporation, shaping rain formation.
To investigate this further, scientists asked what happens when evaporation from soil is unusually low. They hypothesized that moisture-poor soils can feed back into drought conditions, creating a negative cycle that reduces available moisture for precipitation not only locally but also in regions influenced by moisture transported by winds.
Until now, evidence of self-propagating drought fueled by dry soils remained unproven. The new study provides the first solid data confirming this mechanism.
To test the idea, researchers analyzed forty major drought events in recent history. For each case, they tracked weather patterns across drought zones as the area of influence expanded, allowing them to estimate how much downwind precipitation deficits were due to dry soils.
Up to 30 percent of droughts attributed to self-propagation
The conclusion is clear: during certain isolated months, as much as thirty percent of precipitation deficit can stem from self-propagating drought. The phenomenon is described as drought spreading downwind, drying out more lands and reducing their rain resources.
Experts note that self-propagation appears strongest in subtropical arid regions, including Australia and South Africa, where soil moisture has a strong effect on evaporation. These areas already face limited water resources and host large populations and extensive agricultural activity.
As drylands are projected to expand with climate change, the self-propagating nature of droughts could intensify events, accelerating water scarcity and widening the related social, economic, and environmental costs. Scientists stress the need to address the feedback processes that drive these droughts and to explore strategies that can interrupt the cycle.
Reference work: Nature Geoscience study by the Hydroclimatic Extremes Laboratory at Ghent University, part of the DRY-2-DRY project.
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The environment department continues to study how soil moisture, evaporation, and atmospheric moisture interact to influence rainfall and drought dynamics.