Megadroughts are increasing worldwide — and they’re also becoming both hotter and drier.
Over the last 30 years, Earth has experienced an uptick in both frequency and intensity of these punishing, persistent droughts that can last years to decades, researchers report in the Jan. 17 Science . Such lengthy precipitation deficits not only shrink the drinking water supply, but can also lead to massive crop failures, food insecurity, increased tree mortality and increased incidence of wildfire.
The analysis logs the rising global toll of megadroughts from 1980 to 2018. Each year, multiyear droughts affected an additional 5 million hectares of land, physical geographer Liangzhi Chen of the Swiss Federal Institute for Forest, Snow and Landscape Research in Birmensdorf and colleagues found. But the researchers wanted to assess not just the changing scale of the droughts, but also how prolonged droughts impact ecosystems and humans.
Data on precipitation and evapotranspiration — the transfer of water from soil and plants to the atmosphere — allowed the researchers to identify and map megadroughts during that time period, and rank the events by severity. Using satellite data, the team then analyzed changes in regional greenness during the droughts to assess how they affected vegetation.
Nearly every continent on Earth has been subject to megadrought during this period. The worst was southwestern North America’s long-running dry period, which was particularly severe from 2008 to 2014. That drought was the region’s most extreme in 1,200 years and has helped fuel California’s recent bouts with fire, including January’s unusual wintertime wildfires in Los Angeles County .
Top 10 megadroughts from 1980 to 2018
Megadroughts are becoming more common around the world. Among the most severe events in recent decades were multiyear droughts in the East Congo basin, southwestern North America, central Asia and the southwestern Amazon, according to a new study. Years of greatest impact are listed.
Location Duration
1.
Southwestern North America
2008–2014
2.
Sahel
1981–1987
3.
Central Asia
1998–2005
4.
Congo basin
2010–2018
5.
Southern Africa
1992–1996
6.
Russia
1987–1991
7.
Southwestern Amazon
2010–2018
8.
Russia
2007–2012
9.
Eastern Brazil
2014–2017
10.
Central United States
1987–1990
Globally, grasslands are the ecosystem most affected by megadroughts , the greenness analysis revealed. However, these types of ecosystems appear to be more resilient than other types of vegetation such as tropical and temperate forests, bouncing back relatively soon after a drought ends. And other biomes, such as northern boreal forests, are, despite bouts with dryness, still overall getting greener as the planet warms, as their growing seasons extend.
That may change in the future, the team notes. The growing severity and frequency in Earth’s megadroughts might push even the most resilient ecosystems past their limits.
