Researchers at the University of Texas at Austin have found that the El Niño-Southern Oscillation (ENSO) synchronizes extreme wet and dry conditions across continents. Their study, based on satellite data from 2002 to 2024, reveals how these climate patterns drive simultaneous water crises worldwide. The findings highlight a shift toward more frequent dry extremes since around 2012.
Droughts and floods pose significant threats to ecosystems, economies, and daily life. A new study in AGU Advances demonstrates that ENSO, which encompasses El Niño and La Niña phases in the equatorial Pacific, has been the primary driver of extreme changes in global total water storage over the past two decades.
Total water storage encompasses surface water in rivers and lakes, snow and ice, soil moisture, and groundwater. Using gravity data from NASA's GRACE and GRACE-FO satellites, the team measured changes over areas roughly 300 to 400 kilometers wide. They defined wet extremes as water levels above the 90th percentile and dry extremes below the 10th for each region.
The analysis shows ENSO aligning conditions so distant areas experience unusual wetness or dryness simultaneously. For instance, a mid-2000s El Niño event correlated with severe dryness in South Africa, while the 2015-2016 El Niño linked to drought in the Amazon. Conversely, the 2010-2011 La Niña brought exceptional wetness to Australia, southeast Brazil, and South Africa.
Lead author Ashraf Rateb, a research assistant professor at the UT Jackson School of Geosciences' Bureau of Economic Geology, explained the approach: "Most studies count extreme events or measure how severe they are, but by definition extremes are rare. That gives you very few data points to study changes over time. Instead, we examined how extremes are spatially connected, which provides much more information about the patterns driving droughts and floods globally."
Co-author Bridget Scanlon emphasized the implications: "Looking at the global scale, we can identify what areas are simultaneously wet or simultaneously dry. And that of course affects water availability, food production, food trade -- all of these global things."
The study also notes a global shift around 2011-2012, with dry extremes becoming more prevalent afterward, possibly due to enduring Pacific Ocean patterns. To address data gaps, including an 11-month hiatus between GRACE missions in 2017-2018, researchers applied probabilistic models.
JT Reager, deputy project scientist for GRACE-FO at NASA's Jet Propulsion Laboratory, commented: "They're really capturing the rhythm of these big climate cycles like El Niño and La Niña and how they affect floods and droughts, which are something we all experience. It's not just the Pacific Ocean out there doing its own thing. Everything that happens out there seems to end up affecting us all here on land."
Scanlon urged a broader perspective: "Oftentimes we hear the mantra that we're running out of water, but really it's managing extremes. And that's quite a different message." The work was funded by the UT Jackson School of Geosciences.