Flash droughts are raging across the planet

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John Steinbeck tells the dramatic story of an Oklahoma farming family abandoning their drought-stricken land.

The story, made into a film by John Ford and starring Henry Fonda, is based on true events: in the mid-1930s, the great plains of the United States, one of the great breadbaskets of the planet, suffered several years of lack of rains drying the ground so much that enormous dust storms were unleashed.

In the summer of 2012, in the same region where the book and film are set, farmers were expecting a big harvest.

But days after the May corn planting, a sudden drought emerged that wiped out their crops within weeks.

In less than two months, 76% of the crops were affected and the losses exceeded, according to official sources, 30.

000 million dollars.

In terms of water deficit, the event exceeded that novelized by Steinbeck.

A study now shows that these flash droughts are becoming widespread across almost the entire planet, spurred on by climate change.

The 2012 event in the United States put the spotlight on flash droughts.

The original concept,

, was first raised 10 years earlier.

But they have always been there.

What differentiates these phenomena from hydrological droughts is the speed and intensity.

A slow, conventional drought occurs after months or years of below-average rainfall.

The sudden ones arise and reach their maximum in weeks, sometimes days.

Another of its distinctive elements is that they are the result of a complex process that does not stop at the scarcity of rain.

Between the soil (and vegetation) and the atmosphere there is an unstable balance of moisture exchange.

Under normal conditions, rain waters soils and plants that provide moisture to the air through evaporation from the soil and transpiration from the leaves (evapotranspiration).

But if it doesn't rain,

the atmosphere continues to require a contribution of water that steals from the surface and the vegetation.

If there is a heat wave or dry winds in a place where it has not rained in a while, then a flash drought breaks out.

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Now, a group of Chinese and American researchers have analyzed the data available since 1951 to detect the evolution and distribution of flash droughts.

The work, published in the scientific journal

, shows an upward trend in these events both in the territory and in time.

Geographically, these droughts are occurring more in the humid regions of the planet, from Canada to Siberia, passing through the Gulf of Guinea, the Amazon rainforest or the jungles of Southeast Asia and the large islands of Indonesia and Papua New Guinea.

In these parts of the world, the frequency of flash droughts is up to three times higher than in the rest of the planet.

But the problem is global and it is getting worse.

The frequency of flash droughts has increased on 74% of the planet's surface, excluding the poles.

There are several reasons: a decrease in rainfall, a global rise in temperature, an increase in the frequency, intensity and duration of heat waves... After these most affected regions, others more accustomed to droughts appear on the list, be they hydrological or sudden: Sahel and Maghreb in Africa, northern Australia, eastern and central Mexico, eastern Asia, etc.

“The onset speed has increased due to climate change, resulting in a transition to flash droughts”

Xing Yuan, a researcher at the School of Hydrology at Nanjing University (China)

The dean of the School of Hydrology of the University of Nanjing (China) and main author of this research, Xing Yuan, explains in an email that “drought was a phenomenon of slow evolution;

however, the onset rate has increased significantly due to climate change, resulting in a transition to flash droughts.”

This greater intensity and speed would be generating new impacts.

“Vegetation may have less time to adapt to these quick-onset droughts and they pose a huge challenge to early warning systems.

We don't have enough time to prepare for a flash drought," Yuan adds.

For David Walker, a drought researcher at Wageningen University (the Netherlands), "it makes sense that, with warmer temperatures caused by climate change, we have greater evapotranspiration, so we can expect more droughts."

But, Walker adds, "Yuan's work shows us that, in addition to having more droughts, they will come faster, and that transition is already happening."

Regarding the spatial distribution, Walker recalls that a drought "only matters when it affects society, the economy and/or the environment."

So even though these events are most frequent in humid regions, they are generally in a better condition to deal with them.

“The threat, or risk, is probably greatest in arid and semi-arid regions, which have fewer water resources available for supplementary irrigation and suffer more from land degradation.

Furthermore, many of them are generally poorer, with extra factors such as political instability and conflicts”, he concludes.

"The risk is greater in arid and semi-arid regions, which have less water resources available"

David Walker, drought researcher at Wageningen University (The Netherlands)

In 2021, work similar to Yuan's also reached similar conclusions.

His analysis, which started from more recent dates (1980), provided an extra: it related the distribution of flash droughts with the large agricultural areas.

That work found that the impact was being global: the corn belt of the great plains of the United States, as it happened in 2012;

the vast wheat farmlands of southwestern Russia and Ukraine;

the rice growing regions of India and the Indochinese peninsula;

vast areas of the Sahel where millet and sorghum are grown;

and the barley lands of Spain, the world's third largest producer of this cereal.

The meteorologist at the University of Oklahoma, Jordan Christian, co-author of this other work, points out in an email that the greatest challenges posed by flash droughts compared to conventional droughts are related to timing: "Flash drought causes the same impacts as a slower developing drought (decrease in agricultural yields, impacts on livestock, stress on ecosystems...), but at a much faster rate.

This impact over time creates challenges in early warning systems and reduces response times for mitigation strategies."

As the 2012 event in the United States demonstrated, a flash dry month in May does not have the same impact as it does in October.

"What we are experiencing now in Spain is not a sudden drought, it is hydrological, caused by a prolonged rainfall deficit"

Sergio Vicente Serrano, scientist at the Pyrenean Institute of Ecology (IPE–CSIC)

"What we are experiencing now in Spain is not a sudden drought, it is hydrological, caused by a prolonged rainfall deficit," highlights Sergio Vicente Serrano, from the Pyrenean Institute of Ecology (IPE-CSIC).

"But in May of last year we had a heat wave and it is estimated that the cereal harvest was reduced by 25%."

Vicente Serrano is one of the creators of the Flash Drought Monitor and who in 2020 published, together with colleagues from the IPE and the University of Zaragoza, a work similar to that of Yuan and Christian with data from 1961, but focused on the Iberian Peninsula and the Balearic Islands. .

His results are, to a certain extent, the same but on a smaller scale.

Thus, the frequency of sudden droughts is greater in the north and northwest, that is, in humid Spain.

What they did not find is a clear upward trend in frequency,

The cause of the increase in sudden droughts, for the Spanish scientist, is also global warming.

And he gives a piece of information: “In these 60 years, the average annual atmospheric demand [for humidity] per square meter has risen by 125 liters, from 1,100 liters in 1961 to 1,200 liters now.

If we do not have those 1,200 liters, stress is produced in the plants, the crops, the soil”.

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