Scientists have found that ocean temperature patterns may help keep droughts from spreading across the world all at once. The research, led by the Indian Institute of Technology Gandhinagar (IITGN) with international collaborators, suggests that natural climate shifts in the oceans act as a kind of global brake on synchronized drought.
Published in Communications Earth & Environment , the study examined climate records from 1901-2020. The researchers found that synchronized droughts affected only 1.8% to 6.5% of the planet's land area at the same time. That estimate is much lower than earlier claims suggesting that as much as one-sixth of Earth could dry out simultaneously.
The study was led by Dr. Udit Bhatia, along with co-authors from IITGN and the Helmholtz Centre for Environmental Research -- UFZ, Leipzig, Germany. The team investigated how droughts in distant regions line up in time and what factors influence whether they spread together or remain separated.
"We treated drought onsets as events in a global network. If two distant regions entered drought within a short time window, they were considered synchronized," explained Dr. Bhatia, the lead author and the principal investigator of the Machine Intelligence and Resilience Lab and the AI Resilience and Command (ARC) Centre at IITGN.
By tracing thousands of drought connections around the world, the researchers identified several major 'drought hubs.' These included Australia, South America, southern Africa, and parts of North America. The team also examined historical yields of wheat, rice, maize, and soybean to understand how moderate drought affects food production.
"In many major agricultural regions, when moderate drought occurs, the probability of crop failure rises sharply -- often above 25%, and in some areas, above 40-50% for crops like maize and soybean," said Hemant Poonia, an AI Scientist at IITGN who completed his undergraduate and postgraduate degrees in Civil Engineering from the Institute.
Those risks would be especially alarming if many major farming regions entered drought at the same time. However, the study found that natural climate behavior, particularly shifts in sea-surface temperatures in the Pacific and other oceans, helps restrict how far and how evenly droughts can expand.
El Niño and La Niña Reshape Drought Patterns
One major force behind these global shifts is the El Niño-Southern Oscillation, a natural warming-cooling cycle in the Pacific Ocean that affects rainfall patterns worldwide.
During El Niño years, Australia often emerges as a major drought hub, while other areas respond in different ways. During La Niña, the pattern changes again, and droughts often become more spread out geographically rather than concentrated in one global pattern.
"These ocean-driven swings create a patchwork of regional responses, limiting the emergence of a single, global drought covering many continents at once," explained co-author Danish Mansoor Tantary, a former IITGN master's student pursuing his PhD at Northeastern University (USA).
Rainfall Remains the Main Driver of Drought Severity
The researchers also explored how rainfall and temperature work together to influence drought severity. Their analysis found that, in recent decades, roughly two-thirds of long-term changes in drought severity can be linked to precipitation changes. The remaining one-third is tied to rising evaporative demand driven by warming temperat…