In a study in AGU Advances, scientists at The University of Texas at Austin report that the El Nino Southern Oscillation, or ENSO, has been the dominant influence on global total water storage extremes since 2002, synchronizing wet and dry conditions across continents.
Study co author Bridget Scanlon, a research professor at the Bureau of Economic Geology at the UT Jackson School of Geosciences, said that identifying how extremes unfold worldwide has major implications for humanitarian planning and policy.
"Looking at the global scale, we can identify what areas are simultaneously wet or simultaneously dry," Scanlon said. "And that of course affects water availability, food production, food trade - all of these global things."
Total water storage is a key climate metric that sums all water in a region, including surface water in rivers and lakes, snowpack, soil moisture, and groundwater.
The new analysis is among the first to track total water storage extremes and ENSO together at the global level, allowing researchers to examine how far flung water extremes connect, said lead author Ashraf Rateb, a research assistant professor at the Bureau of Economic Geology.
"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," Rateb said. "Instead, we examined how extremes are spatially connected, which provides much more information about the patterns driving droughts and floods globally."
The team used gravity measurements from NASA's GRACE and GRACE Follow On (GRACE FO) satellite missions to estimate total water storage at spatial scales of roughly 300 to 400 kilometers, an area similar to the size of the U.S. state of Indiana.
They defined wet extremes as values above the 90th percentile of total water storage for a region and dry extremes as values below the 10th percentile.
The results show that abnormal ENSO activity can push distant regions into wet or dry extremes at the same time.
Dry extremes line up with El Nino events in some regions and with La Nina in others, with the opposite relationship for wet extremes.
For example, South Africa experienced dry extremes during an El Nino event in the mid 2000s, while the Amazon saw severe drying during the strong 2015 to 2016 El Nino.
In contrast, the 2010 to 2011 La Nina corresponded to extremely wet conditions in Australia, southeast Brazil, and South Africa, illustrating ENSO's capacity to synchronize water extremes across continents.
Beyond the immediate ENSO signal, the researchers identified a global shift in water extremes around 2011 to 2012.
Before 2011, wet extremes dominated the global pattern.
After 2012, dry extremes became more common, a transition the team links to a decade long climate pattern in the Pacific that modulates ENSO's impacts on land water storage.
Because GRACE and GRACE FO observations do not cover the entire period continuously, including an 11 month gap between missions in 2017 to 2018, the scientists used probabilistic models based on spatial patterns to reconstruct total water storage extremes when satellite data were unavailable.
Altogether, the GRACE and GRACE FO records provide a 22 year window from 2002 to 2024, which is short in climate terms but still reveals how tightly climate and terrestrial water are coupled worldwide, said JT Reager, deputy project scientist for the GRACE FO mission at NASA's Jet Propulsion Laboratory and JPL Discipline Program manager for the Water and Energy Cycle.
"They're really capturing the rhythm of these big climate cycles like El Nino and La Nina and how they affect floods and droughts, which are something we all experience," Reager said. "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 said that recognizing water extremes as part of broader climate cycles underscores the need to plan for variability rather than treating scarcity as a simple depletion problem.
"Oftentimes we hear the mantra that we're running out of water, but really it's managing extremes," Scanlon said. "And that's quite a different message."
The research was supported by the UT Jackson School of Geosciences.
Research Report:Dynamics and Couplings of Terrestrial Water Storage Extremes From GRACE and GRACE FO Missions During 2002 2024
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