Droughts are getting longer and more intense (and humans are to blame)

Droughts are getting more frequent, lasting longer and becoming more intense, and pollution is to blame, a new study has shown.

Over the past 100 years, the probability of longer-lasting more intense dry spells has grown in the Americas, the Mediterranean, western and southern Africa and eastern Asia, the study found.

Researchers from the University of California, Irvine (UCI) say that the increasing droughts are caused by greenhouse gases and aerosol pollution.

In the Northern Hemisphere, much of the problem is being caused by aerosols - particles in the air released from power plants, car exhaust and biomass burning

Lead author Felicia Chiang, who conducted the project as a UCI graduate student in civil & environmental engineering, said: “There has always been natural variability in drought events around the world, but our research shows the clear human influence on drying, specifically from anthropogenic aerosols, carbon dioxide and other greenhouse gases.”

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Chiang says that the research showed that several characteristics of droughts are changing - including frequency, duration and intensity - due to human influence.

The researchers used the Coupled Model Intercomparison Project Phase 6 climate simulation platform to compare several scenarios, including a ‘natural’ scenario and others with the addition of greenhouse gas.

When the team modelled accounting for anthropogenic greenhouse gas and aerosol contributions, increases occurred in drought hotspots in southern Europe, Central and South America, western and southern Africa and eastern Asia.

The team says that greenhouse gases had a bigger impact in the Mediterranean, Central America, the Amazon and southern Africa.

Aerosols - particles suspended in the air - played a larger role in Northern Hemisphere monsoon areas and sub-arctic regions.

Aerosols can come from power plants, car exhaust and biomass burning (fires to clear land or to burn farm waste).

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Co-author Amir AghaKouchak, UCI professor of civil & environmental engineering and Earth system science, said: “Knowing where, how and why droughts have been worsening around the world is important, because these events directly and indirectly impact everything from wildlife habitats to agricultural production to our economy.

“Lengthy dry spells can even hamper the energy sector through disruptions to solar thermal, geothermal and hydropower generation.”

Co-author Omid Mazdiyasni, who earned a PhD in civil and environmental engineering at UCI in 2020 and is now a project scientist with the Los Angeles County Department of Public Works, said: “To make matters worse, droughts can be accompanied by heat waves, and high heat and low moisture can increase wildfire risk, which is already significant in the western United States.”

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Mazdiyasni said that while the research paints a gloomy picture of the unwanted impact of humans on the global environment, it points to a potential solution.

He said, “If droughts over the past century have been worsened by human-sourced pollution, then there is a strong possibility that the problem can be mitigated by limiting those emissions."

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