Study Says Multi-Year Droughts Are Expanding Faster than Ever

As climate change accelerates, prolonged dry spells threaten ecosystems, agriculture, and global water security. Over the past four decades, multi-year droughts have become more frequent, longer, and intense.

This is according to a groundbreaking study by the Swiss Federal Research Institute (WSL) published in Science on January 16, 2025,

Researchers found that from 1980 to 2018, the area affected by these droughts grew by about 50,000 square kilometres yearly. The most significant drop in plant health during droughts occurred in temperate grasslands, while forests in colder (boreal) and tropical regions were less affected. But in extreme water shortages, the trees can die, explains Dirk Karger from WSL, who led the study.

‘Multi-year droughts cause enormous economic damage, for example in agriculture and power generation,’ says Karger.

The team of researchers analysed meteorological data from the past 40 years to identify drought conditions. They calculated anomalies in precipitation and evapotranspiration (the evaporation of water from soil and plants). They developed an index and monitored changes in vegetation during these events using global satellite data.

The researchers’ method has demonstrated accuracy in modelling past droughts across various regions, such as the western United States during the severe drought from 2008 to 2014, Australia’s intense dry spell between 2017 and 2019, and Mongolia’s prolonged drought from 2000 to 2011. Notably, they have also been able to model this condition in hard-to-reach regions, such as the Congo rainforest, which experienced significant dry spells from 2010 to 2018.

The researchers also systematically rank these drought events by severity based on the extent of the affected area, duration, and intensity. Utilising the index, they further estimate the impacts of multi-year droughts on global vegetation.

These prolonged drought events can reduce soil moisture, leaving rivers, lakes, and reservoirs dry. According to the study, this can cause devastating impacts, such as massive crop failures, tree mortality, and diminished water supply.

Increased evapotranspiration, decreased rainfall, and rising temperatures contribute to the worsening of these multi-year droughts.

Research shows that the “precipitation deficit”—the difference between actual rainfall and the expected amount over a specific period and area—has steadily increased.

Learn more by clicking the link to the study in the “Sources” section below.