Ocean temperatures may be shielding Earth from a planet-wide 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.

Mapping Drought as a Global Network

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.

Drought Hubs and Crop Failure Risk

"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 temperatures.

"Rainfall remains the dominant driver globally, especially in regions like Australia and South America, but the influence of temperature is clearly growing in several mid-latitude regions, such as Europe and Asia," noted Dr. Rohini Kumar, the corresponding author and senior scientist from the Helmholtz Centre for Environmental Research, who works at the water-land-climate nexus.

A New Way To Protect Global Food Supplies

The findings show how data-driven climate research can help improve strategies for protecting global agriculture. Instead of focusing only on isolated weather events, the team looked at Earth as an interconnected system. That approach could help scientists identify 'early warning' regions before a local drought begins to affect global food markets.

Prof Vimal Mishra emphasized that these findings have important implications for planning, trade, and food security.

"These findings underline the importance of international trade, storage, and flexible policies. Because droughts do not hit all regions at the same time, smart planning can use this natural diversity to buffer global food supplies." Prof Mishra is a leading expert in water and climate at IITGN and a recipient of the Shanti Swarup Bhatnagar Prize, India's highest multidisciplinary science award.

Climate Planning in a Warming World

Dr. Bhatia said the research offers a more hopeful message about drought risk in a changing climate.

"Our research highlights that we are not helpless in the face of a warming planet," said Dr. Bhatia. "By understanding the delicate balance between oceans, rainfall, and temperatures, policymakers can focus their resources on specific drought hubs and create pipelines to stabilize the global market before crop failures in one region trigger price spikes in another."

The authors acknowledge support from the Anusandhan National Research Foundation (SERB) Network of Networks grant, Projekt DEAL, and AI Centre of Excellence (AICoE) in sustainable cities.