Megadroughts are becoming more frequent and severe

Prolonged multi-year droughts, increasingly common since 1980, are set to intensify with ongoing climate warming, according to a new global study.^. 

Led by the Swiss Federal Institute for Forest, Snow, and Landscape Research (WSL) in collaboration with the Institute of Science and Technology Austria (ISTA), this study presents a forty-year quantitative inventory of megadroughts.

The goal is to better inform policy on human-induced climate change and uncover previously unnoticed drought events.

More frequent severe megadroughts

The study reveals a worrying trend: megadroughts are becoming longer, more frequent, and more severe, affecting larger areas worldwide. 

On average, since 1980, drought-stricken regions have expanded by an additional 50,000 square kilometers each year – roughly the combined area of Slovakia or the US states of Vermont and New Hampshire. This expansion has caused enormous damage to ecosystems, agriculture, and energy production.

“Each year since 1980, drought-stricken areas have spread by an additional fifty thousand square kilometers on average – that’s roughly the area of Slovakia, or the US states of Vermont and New Hampshire put together – causing enormous damage to ecosystems, agriculture, and energy production,” said Professor Francesca Pellicciotti, the principal investigator of the WSL-funded EMERGE Project.

One stark example of these trends is the fifteen-year megadrought in Chile, the longest in a thousand years. It has nearly depleted the country’s water reserves, severely impacting agriculture and vital mining operations. 

Despite their devastating effects, many droughts only gain attention when they visibly harm agriculture or forests, meaning subtler yet severe events often go unnoticed.

Identifying hidden droughts

To address the challenge of consistently identifying extreme multi-year droughts, the researchers analyzed global meteorological data from 1980 to 2018, using CHELSA climate data dating back to 1979 provided by WSL. 

By calculating anomalies in rainfall and evapotranspiration – the combined evaporation and plant transpiration – they were able to map the occurrence of megadroughts across the planet, even in remote areas like tropical forests and the Andes.

“Our method not only mapped well-documented droughts but also shed light on extreme droughts that flew under the radar, such as the one that affected the Congo rainforest from 2010 to 2018,” explained Dirk Karger, a senior researcher at WSL and co-author of the study.

This approach allowed the team to detect droughts in less accessible regions, where limited observational data often left events unrecorded. 

The findings highlight how ecosystems respond differently to drought, with temperate grasslands being most severely affected, while boreal and tropical forests initially showing resilience or unexpected responses.

Varied impact on ecosystems

Megadroughts have contrasting effects on different ecosystems. Temperate grasslands have borne the brunt, suffering immediate impacts from prolonged dryness.

The analysis identified hotspots including the western USA, southeastern Australia, and central Mongolia, where severe ecological droughts have been well-documented.

In tropical and boreal forests, responses are more complex. Tropical forests may temporarily buffer drought effects if they hold sufficient water reserves, but prolonged shortages can lead to tree death and long-lasting damage. 

Boreal forests, on the other hand, have experienced paradoxical effects during drought onset due to warmer temperatures lengthening their growing season, though extended droughts could eventually overwhelm these systems.

“In the event of long-term extreme water shortages, trees in tropical and boreal regions can die, leading to long-lasting damage to these ecosystems. Especially, the boreal vegetation will likely take the longest to recover from such a climate disaster,” Karger noted.

Clear trends of intensification 

The researchers produced the first globally consistent, high-resolution map of megadroughts and their vegetation impacts, capturing clear trends of intensification over the past forty years. 

However, the long-term consequences of these events on the planet’s ecosystems are still largely unknown. While some areas, like the pan-Arctic, show increased greening, persistent water shortages could lead to irreversible damage.

“Currently, mitigation strategies largely consider droughts as yearly or seasonal events, which stands in stark contrast to the longer and more severe megadroughts we will face in the future,” Pellicciotti said. 

“We hope that the publicly available inventory of droughts we are putting out will help orient policymakers toward more realistic preparation and prevention measures.”

By making their inventory publicly available, the team aims to guide policymakers in developing more accurate and effective drought mitigation and prevention strategies. 

As part of this effort, Pellicciotti is also examining how mountain glaciers might buffer megadrought impacts through her project “MegaWat – Megadroughts in the Water Towers of Europe – From Process Understanding to Strategies for Management and Adaptation.”

Preparing for frequent megadroughts

This comprehensive inventory of megadroughts serves as a vital tool for understanding the evolving nature of drought in a warming climate. The findings emphasize the urgent need to reevaluate current drought mitigation strategies, which often fail to account for the prolonged and severe nature of future megadroughts.

The study not only changes our perception of drought but also highlights the critical need for improved preparation and policy measures to cope with increasingly severe and persistent drought conditions. 

As climate change progresses, the insights gained from this research will be crucial in shaping a resilient future for ecosystems, agriculture, and water management worldwide.

The study is published in the journal Science. 

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