‘Flash droughts’ coming faster as climate warms, scientists warn

(ORDO NEWS) — Most people have heard of flash floods. On the other hand, “sudden droughts” are not so familiar. Unfortunately, this may change as abnormal, sudden droughts accelerate in the warmer conditions of climate change.

A new analysis of flash droughts shows that droughts have come on faster over the past two decades, with an estimated 33-46 percent of flash droughts now occurring in just five days.

Compared to our traditional understanding of drought a phenomenon that slowly builds up over time due to prolonged rainfall deficits sudden droughts are characterized by a rapid increase in drought conditions, including significant loss of moisture from soils that develop quickly and without warning.

This phenomenon was observed in several countries, including the North American drought of 2012-2013, during which conditions of rapid drought occurred in the central US for several weeks, as well as recent episodes in Australia, China, Africa and other countries.

While these fast events have been documented in many places, there is still much we don’t fully understand about flash droughts and why they occur so quickly.

“Few studies have examined the rapid onset phase of flash droughts and the underlying causes of rapid onset, which is the most important characteristic of flash droughts,” explains the international team in the new study, led by co-authors Yamin Qing and Shuo Wang of the Hong Kong Polytechnic University.

“It is necessary to build a global picture of the onset of drought flare to reveal the spatial pattern and temporal variability in the rate of drought flare, which will improve our understanding of drought flare on a global scale.”

To make this review, the researchers analyzed a 21-year period of hydro-climate data from satellite measurements of rapid and severe declines in soil moisture around the world from 2000 to 2020.

The results suggest that flash droughts are not increasing, but these fleeting events seem to occur even faster over time.

“In particular, the development of flash droughts is accelerating, and ~33.64-46.18 percent of flash droughts occur within five days in the period 2000-2020, which is a big challenge for drought monitoring,” the researchers explain.

“In general, more than 70% of flash droughts develop within a half-moon, and more than 30% of flash droughts develop only within 5 days and are accompanied by high intensity, while traditional droughts can develop within five to six months due to the cumulative impact related climate variables”.

According to the researchers, flash droughts are more likely to occur during episodes of atmospheric drought characterized by high temperatures, low rainfall and high vapor pressure deficits, which exacerbate soil moisture depletion.

From a regional perspective, flash droughts most often occur in humid and semi-humid regions—such as Southeast Asia, East Asia, the Amazon Basin, eastern North America, and southern South America—although they can also occur outside of these hotspots.

“We need to pay close attention to vulnerable regions with a high potential for both soil drought and atmospheric dryness to occur at the same time,” says Wang.

In addition to monitoring vulnerable areas, the findings may help us mitigate the devastating effects of future flash droughts, hoping to more quickly identify them using the criteria defined here, the researchers say.

“To further improve the ability to monitor and predict flash droughts, a criterion of rapid intensity should be considered in addition to a relatively short onset time to capture the unique characteristics of flash droughts,” the researchers conclude.

“Climate change should also be included in the monitoring and forecasting of flash droughts to keep them relevant in a warming climate.”

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