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Droughts can self-propagate: lack of water can spread like wildfire

The lack of evaporation caused in a soil with a lack of moisture can allow droughts to spread on their own, according to recent studies (Getty)
The lack of evaporation caused in a soil with a lack of moisture can allow droughts to spread on their own, according to recent studies (Getty)

The voracity of the forest fires it lies in the ability of fire to spread rapidly, destroying the vegetation around it. Now, European scientists pointed out that another extreme environmental phenomenon, such as droughtsThey also have the quality of self propagateextending and replicating the lack of water to large areas.

Unintentional forest fires and droughts are two climatic phenomena that, like some others, are unpredictable and unmanageable when they happen. However, they are distinguished by the way in which they impact the life of the population in all latitudes, putting at risk everything from economic capital to the very lives of humans and animals.

“Up to 30% of the rainfall deficit can be caused by the self-propagation of drought,” said research from the DRY-2-DRY project of the European Research Council (ERC). According to the document published in the specialized magazine nature geoscience carried out by the Laboratory of Hydroclimatic Extremes of University of Ghent, in Belgiumreduced evaporation caused by dry soil can affect the energy balance of the land surface, with implications for downwind and local precipitation.

Until now, evidence for the self-propagation of drought, fueled by dry soils, lacked proof.  This new study revealed for the first time evidence that confirms this hypothesis (REUTERS / Mike Hutchings)
Until now, evidence for the self-propagation of drought, fueled by dry soils, lacked proof. This new study revealed for the first time evidence that confirms this hypothesis (REUTERS / Mike Hutchings)

When evaporation is limited by soil moisture, the atmospheric supply of water is depleted and this deficit can spread in time and space. According to the hypothesis put forward by the scientists, this mechanism could result in the self-propagation of droughts.

In that sense, already United Nations Organization (UN) warned of extreme weather events including global warming, pollution, and drought, which he has described as “the next pandemic”.

Hundreds of investigations in the world have put the magnifying glass on the protection and stability of the environment with the aim of finding solutions or possible strategies that mitigate a possible future risk. In terms of drought, a comprehensive understanding of the phenomenon opens the door to viable tactics to allow adequate social adaptation.

The absence of rainfall usually manifests itself with dry soils. But the rains are not the only determinant of the humidity. The land surface also plays a very active role in the generation of rain, since it provides moisture to the atmosphere through evaporation.

Droughts account for 15% of natural disasters, but they claimed a large number of victims, approximately 650,000 deaths between 1970 and 2019, the UN said (EPA/PATRICK PLEUL)
Droughts account for 15% of natural disasters, but they claimed a large number of victims, approximately 650,000 deaths between 1970 and 2019, the UN said (EPA/PATRICK PLEUL)

For this reason, the scientists asked themselves for this investigation, what happens when much less water evaporates than normal?

The specialists hypothesized that the lack of evaporation originating from a soil with an absence of moisture may allow droughts to spread on their own, since they offer a negative cycle where they provide less moisture for precipitation, not only locally, but also also in those places where the wind in favor determines the humidity that is transported from the dry soil.

Until now, evidence for this self-propagation of drought, fueled by dry soils, was assumption without proof, however this new study revealed for the first time evidence confirming that hypothesis.

To achieve this, specialists surveyed the 40 most important droughts in recent history. For each event, they tracked the air over the drought regions as the area of ​​influence expanded. This allowed them to calculate how much of the rainfall deficits downwind were caused by dry soils.

The number and duration of droughts have increased by 29% between 2000 and 2022, the UN warned
The number and duration of droughts have increased by 29% between 2000 and 2022, the UN warned

His conclusion was that in isolated months, up to 30% of the rainfall deficit can be caused by this self-propagation of drought. Dominik Schumacher, lead author of the research, said: “In essence, droughts behave similarly to wildfires: while wildfires spread downwind by igniting more and more fuel in their environment, droughts do so.” they do by reducing their own rainfall supply through the drying of the land surface they produce.”

For scientists, then, self-propagation is strongest in subtropical drylands, such as Australia and southern Africa. In these areas the limiting effect of low soil moisture on evaporation is stronger. By definition, water is already scarce in drylands, but these regions support a sizeable fraction of the world’s human population and are also used extensively for agriculture.

Therefore, as drylands are projected to expand as a result of climate change, the self-propagating nature of droughts may lead to even larger and more rapidly-onset events in the future, further exacerbating water scarcity. , as well as the associated socioeconomic and environmental consequences. This is, according to the specialists, “the biggest alarm that must be sounded to find a way out that prevents dry feedback from the processes themselves,” they concluded.

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