The shimmering fields of green energy could leave our planet gasping for water.
Imagine a future where we power our societies not with fossil fuels, but with plants—a world where energy crops capture carbon from the atmosphere, helping to reverse climate change. This promising vision of bioenergy with carbon capture and storage (BECCS) sits at the heart of many global strategies to achieve climate targets. Yet, beneath this green promise lies a hidden dilemma: the massive freshwater resources required to irrigate these energy plantations. While offering a solution to one crisis, could we be inadvertently creating another? Research reveals that irrigating biomass plantations might double the global population living under severe water stress by the end of the century, potentially exceeding the water scarcity impacts of climate change itself 1 .
Bioenergy is the chameleon of the renewable energy world. It can provide liquid fuels for transportation, electricity for our homes, and even offer a pathway to "negative emissions" when combined with carbon capture and storage (BECCS). The process is seemingly elegant: plants absorb CO₂ from the atmosphere as they grow; we convert this biomass into energy and capture the emitted CO₂ for permanent underground storage, effectively creating a carbon sink 1 .
BECCS creates negative emissions by capturing and storing carbon from biomass energy production.
This potential to actively reduce atmospheric carbon has made bioenergy a cornerstone in many climate mitigation models, especially those aiming to limit global warming to 1.5°C. In these scenarios, biomass plantations could expand to cover up to 6 million square kilometers of land, an area roughly the size of Australia 6 .
The fundamental trade-off is simple: to achieve high yields on these vast plantations, many scenarios assume a significant need for irrigation. This "blue water" is drawn from rivers, lakes, and aquifers, putting it in direct competition with drinking water, agriculture, and ecosystem needs.
A comprehensive systematic review of global studies laid bare the astonishing range of potential water demands. The analysis found that future irrigation water withdrawals for bioenergy could span from 128 to a staggering 9,000 cubic kilometers per year 1 4 .
| Category | Projected Global Water Withdrawals for Bioenergy (km³ per year) |
|---|---|
| Lower-end estimates | 128 - 1,000 |
| Higher-end estimates | 2,000 - 9,000 |
| Context: Current global water withdrawals for agriculture, industry, and domestic use | 1,100 - 11,600 |
Comparison of bioenergy water withdrawal estimates with current global water usage
The variation in these estimates stems from different assumptions about key factors, which the review identified as crucial for understanding the full picture 1 :
Some plants are naturally more water-efficient than others.
Growing crops in arid versus humid regions demands vastly different irrigation levels.
The sheer amount of biomass needed in a given climate scenario.
The efficiency of irrigation systems can dramatically alter water usage.
To truly understand the consequences, scientists at the Potsdam Institute for Climate Impact Research (PIK) conducted a detailed computer simulation to compare two futures 3 6 .
The researchers used a sophisticated global vegetation and water balance model (LPJmL) to run two contrasting scenarios for the end of the century:
A world with about 3°C of global warming and only a minimal amount of bioenergy plantations (~30 million hectares).
A world where large-scale, partially irrigated bioenergy plantations (~600 million hectares) are deployed to limit warming to 1.5°C.
They then calculated the Water Stress Index (WSI) for each scenario—a metric that compares total human water withdrawals to the available renewable freshwater in a region. A WSI greater than 40% is considered "high water stress" 3 .
The findings, published in Nature Communications, were striking. While the BECCS scenario successfully curbed climate change, it came with a severe cost for global water resources.
| Scenario | Global Area Under High Water Stress (Million Hectares) | Global Population Under High Water Stress (Billions of People) |
|---|---|---|
| Today | ~1,023 | ~2.3 |
| Climate Change (3°C warming) | ~1,580 | ~4.2 |
| BECCS (1.5°C warming with irrigation) | ~1,928 | ~4.6 |
Comparison of water stress impacts across different scenarios
The simulation showed that in the BECCS scenario, both the global area and population experiencing high water stress would double compared to today, and even exceed the levels projected in the 3°C warming world without large-scale bioenergy 3 . The study identified new hotspots of water stress emerging in regions like eastern Brazil and sub-Saharan Africa, precisely where large-scale biomass plantations were assumed to be located and require intensive irrigation 3 .
Research in this field relies on a combination of powerful computer models and real-world data to simulate complex Earth systems.
Primary Function: Simulates plant growth and the global water cycle
Application: Used to project future water consumption of biomass plantations under different climate scenarios 3 .
Primary Function: Models water quality and quantity at the river basin scale
Application: Assesses impacts of bioenergy crops on local water pollution and irrigation demands .
Primary Function: Links economic, energy, and climate systems
Application: Explores how different climate policies drive bioenergy deployment and its resource use 1 .
Primary Function: A method to determine how much water a river needs to stay healthy
Application: Used as a sustainability standard in models to limit water withdrawals and protect ecosystems 3 .
This research does not mean we should abandon bioenergy. Instead, it highlights the critical need for sustainable water management to be an integral part of any bioenergy strategy 6 . The same PIK study showed that coupling bioenergy plantations with sustainable water practices could almost halve the additional water stress compared to the conventional irrigation scenario 3 6 .
As scientist Fabian Stenzel notes, "Challenging tradeoffs are on the table." The path to a truly sustainable future requires us to balance our climate goals with the imperative of preserving our planet's precious freshwater resources 6 .
Implementing smart water pricing and allocation schemes to discourage waste.
Adopting more efficient irrigation like drip systems, using mulching to reduce evaporation, and building cisterns for rainwater harvesting.
Prioritizing rainfed bioenergy crops and strategically locating plantations in water-rich regions to minimize irrigation needs.
Preserving environmental flow requirements in rivers to ensure the health of aquatic ecosystems amid increased water demand.
A sustainable bioenergy future requires integrated approaches that consider both climate benefits and water resource constraints. Strategic planning, technological innovation, and robust policies can help navigate these trade-offs.