Rethinking subsurface reservoir regulation under climate warming

Global climate change has reshaped the terrestrial water cycle into an asymmetric pattern of water storage partitioning ¹. Hydrological research and water management have long prioritized conventional water shortage issues, while overlooking a critical climate-driven shift ². Warming does not merely alter total water availability, but restructures water storage partitioning among atmospheric, surface and subsurface reservoirs. Structural imbalance across these three compartments arises from overloaded atmospheric and surface water systems in tandem with depleted subsurface water storage. This imbalance has become a core driver of contemporary compound hydrological disasters, yet it remains insufficiently integrated within mainstream water risk assessment and regulation systems.

Thermodynamic enhancement under climate warming fundamentally expands the effective capacity of the atmospheric water reservoir. The Clausius–Clapeyron relation dictates that atmospheric precipitable water rises by approximately 7% per degree of global warming, which continuously inflates the theoretical storage limit of the atmospheric reservoir ³. Unlike steady natural variability, this anthropogenic and non-stationary climate expansion disrupts historical balances in vapour accumulation and precipitation release ⁴. Overloaded atmospheric systems generate intensified extreme precipitation events, which exceed the engineered storage and discharge thresholds of surface reservoirs including rivers, lakes and seasonal snowpack. In this context, incremental water accumulation within atmospheric and surface compartments transitions from a natural hydrological feature into a primary trigger of catastrophic fluvial flooding and widespread surface waterlogging worldwide.

Widespread and persistent depletion of subsurface reservoirs counteracts the overloaded status of upper terrestrial water compartments. Long-term unregulated groundwater extraction for agricultural, industrial and domestic purposes has emptied substantial aquifer storage across most mid-latitude and arid or semi-arid regions ⁵. This large-scale subsurface water deficit reflects a critical cognitive and managerial mismatch in global water governance. The planet hosts extensive vacant subsurface storage with strong natural regulation potential, yet human societies have passively depleted this strategic reservoir instead of proactively utilizing its buffering capacity. Continuous groundwater over-extraction compresses aquifer porosity, induces irreversible land subsidence, weakens baseflow support for surface water bodies, amplifies seasonal drought risks, and breaks the inherent self-regulating properties of terrestrial hydrological systems.

We argue that subsurface reservoirs should be elevated to the core regulatory hub and natural safety valve of the tripartite water system, and they provide infrastructure-scale solutions to climate-induced structural hydrological imbalance. To formalize this climate-adaptive regulation mode, we define an innovative conceptual framework named Strategic Groundwater Banking under Climate Extremes. Distinct from conventional routine groundwater recharge designed for water supply augmentation, this extreme-oriented strategic framework treats depleted aquifers as flexible and climate-resilient water storage infrastructure. The framework proactively captures transient flood surpluses generated by overloaded atmospheric and surface reservoirs during extreme rainfall events, stores excess water within subsurface reservoirs, and sustains controlled water release throughout dry periods. This paradigm redefines subsurface water storage as a coupled human–natural climate adaptation infrastructure that balances perturbed tripartite hydrological cycling, rather than a passive hydrological component.

Global pilot practices have verified the feasibility and effectiveness of Strategic Groundwater Banking through Flood-Managed Aquifer Recharge (Flood-MAR). Flood-MAR represents a targeted climate-adaptive intervention that converts destructive extreme flood surpluses into sustainable subsurface water reserves ^6,7. Widespread aquifer depletion in California has created billions of cubic meters of vacant subsurface storage. Local water authorities implement targeted Flood-MAR schemes to divert peak flood runoff from winter atmospheric river precipitation into alluvial aquifers, which mitigates fluvial flooding and replenishes long-term groundwater reserves simultaneously. Drought-prone regions in India have also adopted community-scale flood recharge projects. These initiatives transform damaging monsoon flood surpluses into durable subsurface water assets that buffer pre-monsoon water scarcity. Such real-world case studies confirm the capacity of subsurface reservoirs to buffer climate-driven hydrological extremes and validate the practical value of coordinated tripartite reservoir regulation.

Coordinated tripartite reservoir regulation rebuilds beneficial land–atmosphere feedback loops and reverses current hydrological vicious cycles ^8,9. Sustained subsurface water recovery elevates regional soil moisture levels, stabilizes terrestrial vegetation coverage, and enhances evapotranspiration (ET) fluxes. Restored ET strengthens land-to-atmosphere water recharge, stabilizes local vapour cycling, and buffers extreme fluctuations in atmospheric reservoir storage under climate warming. This mechanism transforms passive disaster response into active cyclic water regulation. Floodwater replenishes groundwater storage, groundwater sustains ecological hydrological processes, and ecological evapotranspiration stabilizes regional atmospheric water balance.

The operationalization of Strategic Groundwater Banking and tripartite coordinated regulation requires a unified and full-dimensional monitoring and scheduling framework. Current GRACE satellite products capture surface and subsurface water storage anomalies but exclude atmospheric reservoir dynamics, which results in incomplete water balance assessments and biased extreme risk forecasting ¹⁰. We demonstrate a framework to support a global proactive climate-adaptive scheduling chain. Key procedures include the pre-emptive prediction of extreme atmospheric water loading, pre-discharge of partial surface reservoir capacity, Flood-MAR implementation for strategic subsurface floodwater banking, and sustained maintenance of ecological baseflow during dry seasons (Fig.1). This integrated system transforms fragmented water management practices into systematic climate adaptation governance.

Climate warming has fundamentally restructured terrestrial hydrology into a perilous unbalanced tripartite system. Thermally inflated atmospheric and surface reservoirs generate frequent extreme flood hazards, while chronically depleted subsurface reservoirs lose their natural drought buffering capacity ¹¹. The absence of large-scale Strategic Groundwater Banking and tripartite coordinated regulation will expose human societies to mutually reinforcing dual global water crises ¹². Saturated surface storage leaves no buffering space for extreme wet seasons and triggers catastrophic flooding, while exhausted subsurface baseflow induces severe water scarcity and river desiccation during dry seasons. The subsurface reservoir functions as a unique dual-function safety key that mitigates both flood and drought risks through cross-temporal bridging of climatic water surplus and deficit. A governance shift from passive surface hazard mitigation to proactive subsurface-centered tripartite strategic management delivers a critical paradigm upgrade for climate-resilient water security ¹³. This framework provides a globally scalable and actionable blueprint for modern water policy, and it fulfills the interdisciplinary impact and forward-looking perspective required for Nature Geoscience commentary.

Fig. 1 The triad of terrestrial water reservoirs: a coupled atmospheric, surface, and subsurface system with regulatory valves for climate adaptation.

Schematic of the climate-driven unbalanced tripartite water system and anthropogenic strategic regulation pathways. The upper atmospheric reservoir (water vapor, clouds; 8–10 d residence time) features warming-induced capacity expansion via the Clausius–Clapeyron effect, with dual moisture sources of cross-basin atmospheric river transport and local terrestrial recycling, driving increased extreme precipitation and surface water overloading. The middle surface reservoir (lakes, rivers, snowpack; weeks to years residence time) accumulates excess floodwater under climatic extremes, constituting the primary source of fluvial hazards. The lower subsurface reservoir (groundwater, soil moisture; months to millennia residence time) suffers from chronic storage depletion due to anthropogenic pumping, forming massive vacant storage space for climate adaptation. Vertical hydrological fluxes connect the three reservoirs: precipitation (P) delivers atmospheric water to the surface system, evapotranspiration (ET) mediates land–atmosphere feedback regulated by land use, infiltration (I) enables surface-to-subsurface recharge, and anthropogenically modulated discharge (Q) dominates subsurface water loss. Climate warming acts as an external driver to inflate atmospheric reservoir capacity and enhance ET demand, triggering upper-reservoir overloading and hydrological volatility. Human regulatory valves are upgraded to Strategic Groundwater Banking via Flood-MAR: targeted floodwater recharge transfers surplus hazardous surface water into depleted aquifers, serving as a dual safety valve to mitigate flood risk in wet seasons and sustain baseflow in dry seasons. This human–nature co-regulation model rebuilds balanced tripartite water cycling and beneficial land–atmosphere feedbacks, realizing climate-resilient terrestrial water management.

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