Why the planet doesn’t dry out together: scientists solve a global climate puzzle

Researchers at the Indian Institute of Technology Gandhinagar (IITGN), in collaboration with international partners, have shown that ocean temperature patterns help limit the global spread of droughts. Published in Communications Earth & Environment, the study analysed climate data from 1901–2020 and found that synchronised droughts affected between 1.8% and 6.5% of global land, far lower than earlier claims that one-sixth of the planet could dry out at once.

The study, led by Dr Udit Bhatia, with co-authors from IITGN and the Helmholtz Centre for Environmental Research – UFZ, Leipzig, Germany, examines how droughts in different parts of the world align in time and what controls their spread. “We treated drought onsets as events in a global network. If two distant regions entered drought within a short time window, they were considered synchronised,” 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 mapping thousands of such connections, the team identified ‘drought hubs’ in Australia, South America, southern Africa, and parts of North America. In parallel, they analysed historical yields of wheat, rice, maize, and soybean to assess 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. While this could be catastrophic if many regions dried out at once, the study shows that natural climate processes, especially changes in sea‑surface temperatures in the Pacific and other oceans, limit how far and how uniformly droughts can spread.

A major driver of these shifts is the El Niño–Southern Oscillation, a natural warming-cooling cycle in the Pacific Ocean that reshapes rainfall worldwide. During El Niño years, Australia becomes a prominent drought hub, while other regions respond differently. During La Niña, drought patterns shift again, often becoming more geographically dispersed. “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). 

The team also studied the interplay between rainfall and temperature to understand how both factors drive drought severity. The authors found that, over recent decades, about two‑thirds of the long‑term changes in drought severity can be traced to changes in precipitation, with the remaining one‑third linked to warming‑driven increases in evaporative demand. “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.

The study highlights how data-driven research about climatic impact on global agricultural zones can transform our approach to safeguarding the world’s food supply. By moving beyond isolated weather reports and looking at the Earth as an interconnected network, the team has created avenues to identify ‘early warning’ regions before a local dry spell becomes a global crisis. 

Highlighting the broader implications, Prof Vimal Mishra said, “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.

“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 stabilise 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.