Executive Summary
A paradigm shift is rewriting our understanding of sea level rise: while oceanographers and glaciologists have focused on polar ice dynamics, satellite gravimetry has revealed that continental water loss—traditionally the domain of hydrologists—now contributes more to rising seas than melting ice sheets. According to a 2025 study published in Science Advances, groundwater depletion accounts for approximately 68% of global freshwater loss, with groundwater depletion contributing about 0.8 mm per year to global sea level rise.
Four major "mega-drying" regions have been identified: Southwestern North America/Central America, Alaska/Northern Canada, Northern Russia, and Middle East-North Africa, expanding at approximately twice the size of California each year. The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) satellite mission enabled these discoveries through its Laser Ranging Interferometer, which improves measurement precision by at least a factor of 10 compared to previous systems. This technological breakthrough bridges the observational gap between local hydrological measurements and global sea level monitoring, revealing water mass transfers that reshape our understanding of climate system interactions.
Groundwater Depletion Emerges as Dominant Sea Level Driver
The relationship between groundwater depletion and sea level rise represents a fundamental shift requiring integration across previously separate research domains. A 2025 Science Advances study reveals that groundwater depletion—not glacial melt—now accounts for the majority of global freshwater loss, with an estimated 80% of depleted groundwater eventually returning to the ocean.
What makes this discovery particularly significant is how it connects systems typically studied by separate research communities. From 1960 to 2000, global groundwater abstraction increased from 312 km³ to 734 km³ per year, with depletion rising from 126 km³ to 283 km³ per year. Current estimates suggest groundwater depletion adds approximately 0.6 mm/year to sea level rise, projected to increase to 0.82 mm/year by 2050, potentially leading to a total rise of 40 mm above 1990 levels by 2050.
This global-scale connection manifests through distinct regional patterns that reveal how local water management decisions collectively create continental-scale impacts with global consequences. A tipping point occurred around 2014-2015, when groundwater use increased significantly, fundamentally altering the balance between terrestrial water storage and oceanic inputs.
Four Mega-Drying Regions Reshape Global Water Patterns
The four major "mega-drying" regions identified through satellite observations represent more than traditional drought patterns—they indicate fundamental shifts in terrestrial water storage that persist beyond seasonal cycles. The US West Coast has been identified as the worst affected region, with 75% of the global population living in countries experiencing freshwater loss since 2003.
These regions lose water from multiple reservoirs simultaneously—surface water, soil moisture, and deep groundwater—creating compound effects that traditional hydrological monitoring might miss. The scale and rate of expansion suggests continental mega-drying represents a systemic shift in Earth's water cycle rather than temporary anomaly, creating positive feedback loops where groundwater depletion accelerates as surface water shortages intensify pumping demands.
Research published in npj Climate and Atmospheric Science found that terrestrial water storages in drylands have decreased despite increased vegetation growth from 1982 to 2016, predicting a reduction in terrestrial water storage of 41-84% by 2100, coinciding with dryland expansion of 4.1-10.6%.
Coastal Feedback Loops Create Compound Vulnerabilities
Rising seas and depleting groundwater create feedback loops that compound vulnerabilities in coastal aquifers in ways that neither sea level rise models nor groundwater management frameworks adequately capture when operating in isolation. Sea level rise exacerbates groundwater overexploitation and salinization in coastal areas, with approximately 60 million people potentially losing over 5% of their fresh groundwater resources by 2100 under RCP 8.5 scenarios.
In the San Francisco Bay Area, where tech campuses and residential neighborhoods sprawl across former wetlands, groundwater rise is predicted to affect twice as much land as direct inundation from sea level rise. This means infrastructure built on seemingly safe ground—miles from the shoreline—may face flooding from below as water tables rise. Additionally, 326 Superfund sites in the U.S. may be vulnerable to groundwater rise due to sea level rise.
These feedback mechanisms create long-distance hydrological teleconnections that cross traditional watershed boundaries. As seawater intrudes into coastal aquifers, communities often respond by pumping from deeper groundwater sources, which can accelerate subsidence and increase vulnerability to sea level rise, while inland groundwater depletion contributes to the very sea level rise that threatens coastal aquifers.
Satellite Technology Bridges Disciplinary Divides
Before GRACE-FO, scientists lacked tools to quantify continental-scale water mass changes with sufficient precision to connect them to sea level variations—creating decades of parallel but disconnected research. The Laser Ranging Interferometer bridges this historical divide, providing a common observational framework that allows hydrologists and oceanographers to correlate findings and develop integrated models that will reshape climate projections for decades to come.
The technical breakthrough stems from laser wavelengths 10,000 times shorter than microwaves, allowing detection of smaller gravitational differences. Simulations indicate the LRI can improve satellite-to-satellite tracking measurement performance by approximately 23% for wavelengths smaller than 240 km, enabling scientists to detect water mass transfers previously invisible to scientific observation.
This methodological innovation fundamentally changes our ability to track water movement across Earth's surface, revealing connections between terrestrial water management and oceanic processes that traditional monitoring systems missed entirely.
Agricultural Practices Link Local Decisions to Global Consequences
Agricultural water management represents a critical intervention point where local decisions create global consequences. Groundwater supplies approximately two-thirds of irrigation water during droughts, with California's Central Valley exemplifying this dependency—depletion rates increased from 1.86 km³/year (1961-2021) to 8.58 km³/year (2019-2021) during recent megadrought conditions.
Zero Tillage with Deficit Irrigation emerges as the most cost-effective agricultural practice for water conservation, integrating traditional soil management wisdom with precision irrigation technology to address both food security and sea level concerns simultaneously. A 2025 study published in Scientific Reports used fuzzy extent analysis to evaluate agricultural sustainability parameters, finding that combining Zero Tillage with Deficit Irrigation is the most cost-effective practice, enhancing climate resilience and water efficiency.
Managed Aquifer Recharge has been highlighted as a cost-effective strategy for drought resilience, involving intentional groundwater aquifer replenishment to counteract depletion and saltwater intrusion. These practices represent interventions that simultaneously address water security, agricultural productivity, and sea level rise mitigation—a connection largely overlooked in both agricultural policy and coastal management.
Emerging Research Frontiers Demand Integrated Approaches
Addressing the groundwater-sea level connection requires integrated research approaches that transcend traditional disciplinary boundaries. Climate change impacts on groundwater systems don't directly correlate with precipitation trends; instead, they're influenced by increased evapotranspiration and reduced snowmelt, with over-pumping often exceeding natural replenishment rates.
Multi-year global coupled simulations using the Integrated Forecasting System with NEMO and FESOM models achieve atmospheric resolution of 4.4 km, allowing improved representation of small-scale processes that enhance climate prediction accuracy. These models demonstrate significant improvements in water and energy budgets, benefiting operational forecasting.
Another promising approach involves integrating Geographic Information System (GIS) with hydrologic-hydraulic modeling to assess flood risks in coastal areas, evaluating multiple flood drivers including groundwater rise and sea level rise, revealing significant increases in flood inundation areas.
Toward Integrated Water Cycle Science
The continental mega-drying phenomenon represents both challenge and opportunity—a challenge because it adds complexity to climate adaptation problems, but an opportunity because it reveals intervention points in terrestrial water systems that could help mitigate sea level rise while addressing water security concerns.
Moving forward, several research frontiers deserve attention: developing coupled models that dynamically link terrestrial water systems and sea level processes at regional scales; quantifying potential sea level mitigation benefits of large-scale groundwater conservation programs; mapping vulnerability hotspots where groundwater depletion and sea level rise create compound risks; and designing monitoring systems that track water mass transfers across the continuum from inland aquifers to coastal waters.
For philanthropist investors evaluating research landscapes, these findings highlight emerging opportunities at the intersection of water technology, agricultural innovation, and coastal adaptation. The groundwater-sea level connection creates new markets for precision irrigation systems, managed aquifer recharge technologies, and integrated monitoring platforms that serve both agricultural productivity and climate mitigation goals.
By bridging disciplinary divides and developing integrated approaches to water cycle science, researchers can transform this emerging understanding into effective solutions that address water security and sea level rise as interconnected challenges rather than separate problems.
Things to follow up on...
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Digital Twin Earth: A Digital Twin Earth model integrates high-resolution Earth observation data with advanced hydrological modeling to enhance decision-support systems for predicting and managing water-related environmental disasters.
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GPS Drought Monitoring: Research shows that GPS and GRACE measurements can monitor hydrometeorological changes, including drought characteristics, with Drought Severity Indices showing positive correlations at over 80% of global stations.
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Seawater Intrusion Vulnerability: Studies reveal that approximately 15% of the U.S. coastline has groundwater levels below sea level, increasing vulnerability to seawater intrusion that threatens freshwater supplies for over 100 million Americans.
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Interdisciplinary Training Models: The Western Passage Student Research Collaborative trains undergraduates in interdisciplinary research related to marine renewable energy, emphasizing authentic experiences in research and public decision-making.