Deep-rooted forests are handling the stress much better than our intensive croplands, which are becoming increasingly fragile.
India Water Portal
When India’s groundwater crisis is discussed, the focus usually stays above ground—on wells that run dry, on farmers drilling ever deeper boreholes, and on states locked into unsustainable irrigation subsidies. What is far less visible, yet far more consequential in the long run, is how changing groundwater levels are altering the very way India’s ecosystems function.
A recent national-scale study published in Ecological Informatics reveals that groundwater depth is not just a hydrological concern but a fundamental ecological control, shaping how efficiently India’s landscapes convert water into biomass and carbon into growth. Titled “Linking groundwater variability to ecosystem carbon and water use efficiencies across India,” the paper is authored by Abhishek Chakraborty, M. Sekhar, Soumendra N. Bhanja, and Lakshminarayana Rao and represents one of the most comprehensive attempts yet to connect groundwater dynamics with ecosystem productivity across the country.
Their conclusion is stark: as India’s water tables change—whether through over-extraction, irrigation, or climate variability—the country’s croplands, forests, and shrublands are being quietly reprogrammed in how they grow, respire, and use water.
Looking beyond yields: Why efficiencies matter
Most agricultural and water policy debates in India revolve around yields—how many tonnes of rice or wheat a hectare produces. The Chakraborty et al. study shifts attention to something subtler but arguably more important: efficiency. The authors focus on two key indicators. Carbon Use Efficiency (CUE) measures the share of carbon fixed by plants through photosynthesis that actually becomes biomass after accounting for respiration losses. Water Use Efficiency (WUE) measures how much carbon plants fix per unit of water lost through evapotranspiration.
These metrics matter because they capture ecosystem health rather than just output. A system can maintain yields for a while through heavy irrigation and fertiliser use, yet become progressively less efficient—losing more carbon to respiration or more water to unproductive evaporation. Such systems are productive but fragile. By analysing CUE and WUE together, the study provides a rare integrated view of how groundwater influences both the carbon cycle and the water cycle across India’s landscapes.
The hidden importance of water table depth
India has enormous spatial variation in groundwater depth, shaped by climate, geology, and decades of human intervention. The authors classify landscapes into two contrasting regimes:
Shallow water table depth (SWTD): groundwater less than 2 metres below ground level, close enough to influence plant roots through capillary rise.
Deep water table depth (DWTD): groundwater deeper than 8 metres, effectively inaccessible to most crops and natural vegetation.
This distinction is crucial. Shallow groundwater can supplement rainfall and irrigation, buffering plants during dry periods. Deep groundwater, by contrast, removes that safety net.
Using satellite-derived estimates of plant productivity, evapotranspiration, and vegetation health—combined with observation-constrained groundwater models and well data—the authors compare how ecosystems perform under these two regimes across six of India’s major hydro-climatic zones.
When shallow groundwater helps; and when it hurts
Across much of semi-arid and sub-humid India, the results confirm what agronomists have long suspected: shallow groundwater boosts ecosystem performance. Regions with shallow water tables show higher gross and net primary productivity and higher evapotranspiration, reflecting better plant access to moisture. This translates into 8–12% higher carbon and water use efficiencies, particularly in croplands and dry forests.
In these landscapes, shallow groundwater acts as a stabiliser. It supports crops during dry spells, sustains transpiration, and keeps photosynthesis going when rainfall falters. This is especially evident in semi-arid regions where rainfall alone would be insufficient.
But the picture reverses in India’s humid and intensively irrigated zones. In parts of eastern India, the Western Ghats, and heavily puddled rice systems, deep groundwater zones sometimes exhibit higher carbon efficiency than shallow ones.
The explanation lies in soil physics and plant physiology. When water tables are too shallow in already wet environments, soils can become waterlogged. Oxygen availability drops, root respiration becomes inefficient, and plants lose more carbon through stress-related respiration. Photosynthesis may continue, but net carbon gain declines.
In such contexts, slightly deeper groundwater allows better drainage and aeration, improving carbon efficiency even if total water availability is lower.
Seasons reveal the real story
One of the study’s strongest contributions is its seasonal analysis, which reveals how groundwater impacts change over India’s cropping calendar.
During the Rabi (dry) season, shallow groundwater clearly benefits irrigated agriculture in northern India. Cooler temperatures, controlled irrigation, and proximity to groundwater allow wheat and other crops to maintain high carbon and water efficiency. Here, shallow groundwater complements irrigation rather than overwhelming soils.
During the Kharif (monsoon) season, the advantage often shifts. In humid regions with heavy rainfall, shallow groundwater can exacerbate waterlogging, reducing both carbon and water efficiency. Deeper groundwater conditions, paradoxically, become more favourable.
These seasonal contrasts explain why blanket prescriptions—such as uniformly promoting groundwater recharge—can have unintended ecological consequences if local conditions are ignored.
Crops, aquifers, and political choices
The paper also highlights how agricultural policy and geology interact with groundwater to shape ecosystem outcomes. Northern India’s alluvial aquifers store vast amounts of water and are supported by subsidised electricity for pumping. This has enabled year-round cultivation of water-intensive crops such as rice and wheat. While this system maintains high water use efficiency—producing more biomass per unit of water—it often suffers from declining carbon efficiency due to high respiration costs under warm, irrigated conditions.
Peninsular India tells a different story. Hard-rock aquifers store limited groundwater and depend heavily on monsoon recharge. Here, falling water tables are strongly associated with declines in both carbon and water efficiency, particularly in croplands. Once groundwater declines beyond a threshold, irrigation cannot fully compensate.
Natural ecosystems show greater resilience. Deep-rooted deciduous forests and shrublands can access moisture from deeper soil layers and adjust leaf area seasonally, maintaining efficiency even as groundwater declines. This contrast underscores how intensive agriculture is far more vulnerable to groundwater depletion than natural vegetation.
What happens when water tables fall
Perhaps the most policy-relevant findings emerge from the analysis of declining groundwater trends.
In large parts of peninsular India, groundwater decline leads to consistent reductions in both carbon and water use efficiency—a clear signal of ecosystem stress. In the Indo-Gangetic Plain, the response is more complex: carbon efficiency declines, but water efficiency often increases, reflecting crops that conserve water under stress but lose net productivity due to high respiration.
This divergence matters. Rising water efficiency may look positive in isolation, but if it comes at the cost of declining carbon efficiency, it signals a system that is becoming less productive and more fragile over time.
Why this matters for climate and policy
The study’s implications extend far beyond groundwater management.
First, groundwater is a climate variable, not just a water resource. By shaping carbon uptake and respiration, water table depth influences how much carbon India’s landscapes can store—a factor rarely considered in climate planning.
Second, irrigation efficiency has ecological limits. Subsidised pumping may sustain production temporarily but can erode long-term ecosystem efficiency, particularly carbon efficiency.
Third, context matters more than averages. Shallow groundwater is beneficial in semi-arid regions and dry seasons, but harmful in humid landscapes and wet periods. Policy must reflect this complexity.
Finally, the findings challenge India’s dominant groundwater narrative. The problem is not simply “too much extraction” or “too little recharge,” but misaligned water use relative to ecology, season, and aquifer type.
A crisis playing out underground
India’s groundwater crisis is often described as a slow-moving disaster. This study shows that it is also a quiet ecological transformation. As water tables fall or rise, ecosystems recalibrate how they use water and carbon—sometimes adapting, sometimes degrading. What happens underground, the authors make clear, will increasingly determine what happens above ground: not just to crops and farmers, but to India’s long-term ecological resilience in a warming, water-stressed future.
Citation: Chakraborty, A., Sekhar, M., Bhanja, S. N., & Rao, L. (2025). Linking groundwater variability to ecosystem carbon and water use efficiencies across India. Ecological Informatics, Volume 91, Article 103411.