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.
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.
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.
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.
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.
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.
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.