Impacts of irrigated agriculture on food-energy-water-CO2 nexus across metacoupled systems

The paper addresses how irrigated agriculture affects the interconnected food-energy-water-CO2 (FEWC) nexus across coupled human and natural systems linked by trade and infrastructure. China faces concurrent challenges of food security, water scarcity, energy use, and CO2 emissions. The North China Plain (NCP) supplies about half of China’s wheat and maize, relying heavily on irrigation and energy, while much of its production is traded to other regions. The study is motivated by gaps in systematic, quantitative analyses of irrigated agriculture’s cross-sector and cross-regional impacts, including overlooked spillover systems affected by interventions like the South-to-North Water Transfer Project (SNWTP). The research questions are: (1) What crop production, energy footprint, water footprint, CO2 emissions, and water and food sustainability are attributable to irrigated agriculture across the NCP? (2) How do environmental and socioeconomic factors (climate change, diet change, irrigation technologies, cropping strategies, water diversion) affect the FEWC nexus in the NCP? (3) What impacts does irrigated agriculture in the NCP impose on spillover systems (e.g., Hubei Province via the SNWTP)?

Prior work has examined environmental impacts of food production and trade, including virtual water flows and embodied energy/greenhouse gas emissions. Irrigated agriculture has particularly profound impacts, and irrigated area for domestic and trade purposes has been increasing globally. Nexus studies have highlighted interconnections among water, energy, food, and CO2, but systematic, quantitative assessments across multiple systems and sectors simultaneously remain limited, especially regarding spillover systems often ignored in policy and research. China’s interregional food trade and water transfers (e.g., SNWTP) have been studied, but integrated assessments linking irrigated production in the NCP to FEWC outcomes across sending, receiving, and spillover systems under varying scenarios are lacking.

The study adopts the metacoupling framework to define and analyze interactions among sending (NCP), receiving (rest of China), and spillover (Hubei Province) systems linked by food trade and water transfers. A life cycle assessment (LCA) approach (ISO 14040/14067) is coupled with water, energy, and carbon footprint analyses across five agricultural stages: tillage, sowing, irrigation, fertilization, and harvest. Water footprint (WF) components include green, blue, and grey water; WF is computed using a crop water production function (CWPF)-based method to estimate actual evapotranspiration and partition green/blue components; grey WF focuses on nitrogen. Energy footprint (EF) accounts for seeds, machinery, labor, fertilizers, pesticides, and irrigation energy. Carbon footprint (CF) covers fertilizer production/use, irrigation, machinery, labor, seeds, and pesticides/herbicides. Data sources include 1986–2010 agrometeorological records (National Meteorological Information Center of China), county-level agricultural data (Chinese Academy of Agricultural Sciences), evapotranspiration measurements (Luancheng Agro-Eco-Experimental Station), and SNWTP construction/materials data (Feasibility Study Report). The AquaCrop model simulates yields under climate and management scenarios. Fifteen scenarios (Baseline and S1–S15) assess climate change (to 2030), irrigation frequency changes, rain-fed conditions in high-flow years, reduced irrigation in low-flow years, irrigation technology upgrades (drip/sprinkler), altered cropping systems (e.g., adding spring maize), diet changes (FAO-recommended grain intake levels), and increased SNWTP deliveries (to maximum). Water sustainability is defined as the ratio of total available agricultural water resources to total water consumption in irrigated agriculture; values >1 indicate sustainability. Sustainable food supply is the ratio of actual production to required production (based on targeted yields times area) to fulfill the NCP’s share of national food security; values >1 indicate sustainability. Spillover effects from the SNWTP are evaluated via hybrid EIO-LCA covering material manufacturing, transportation, construction, and operation over a 50-year horizon; water footprint components include evaporation from open channels and construction/material-related water. Data quality is assessed using a Data Quality Index (DQI) with uncertainty quantified by Monte Carlo simulation (50,000 runs), yielding uncertainties between 3–6%.

• All evaluated NCP counties exhibited unsustainable water use due to irrigated agriculture. The NCP’s total irrigated agriculture water consumption in 2010 was over four times the region’s renewable agricultural water (water sustainability index ≈ 0.23).
• Aggregate impacts for irrigated wheat–maize in the NCP (baseline around 2010) included: WF ≈ 1.78×10^10 m3; CF ≈ 6.55×10^7 t CO2; EF ≈ 4.81×10^12 MJ; Yield ≈ 5.46×10^7 t.
• Despite water unsustainability in the NCP, its crop production met its assigned responsibility for sustainable food supply in the rest of China.
• Scenario outcomes varied widely: • Lowest water footprints: S11 (diet change B, grain intake 94.0 kg/y), S15 (max water transfer + diet change C + drip upgrade and cropping change), S12 (diet change C, grain intake 75.0 kg/y). These also ranked among the lowest energy and carbon footprints. However, S11 and S12 had low water and food sustainability due to reduced yields. • Highest yields (and food sustainability): S5 (drip), S6 (sprinkler), S8 (drip + cropping change). Two of these (S5, S6) also had among the highest energy and carbon footprints, indicating trade-offs where higher yields are driven by greater energy/water inputs. • Water sustainability was not guaranteed under 11 of 15 scenarios (S1–S10 and S13). Food sustainability was not ensured under 7 of 15 scenarios (S2–S4, S7, S10–S12). Only two scenarios achieved both water and food sustainability.
• Strong spatial heterogeneity across NCP counties: water sustainability generally decreased towards the south; water, carbon, and energy footprints showed heterogeneous spatial patterns reflecting differences in production, industrialization, farming practices, and water use.
• Spillover impacts in Hubei Province due to the SNWTP: approximately 9.5 billion m3 of water diverted annually from Hubei to northern China (about 2.1 billion m3 to NCP agriculture); about 310 km2 of land occupied (including ~149.3 km2 cropland, 22.5 km2 shrubland, 44.2 km2 forest, 96.1 km2 other land); life-cycle CO2 emissions associated with the SNWTP were approximately 3.1 million tons; substantial energy use throughout the project’s life cycle. Hubei is minimally involved in direct food trade with the NCP yet bears significant environmental burdens.

Findings reveal cross-sector and cross-regional trade-offs in a metacoupled system: safeguarding food security in receiving regions relies on irrigated production in the NCP, driving unsustainable water use and elevated energy and carbon footprints locally. Spillover systems, notably Hubei Province, incur significant water loss and land occupation due to the SNWTP, despite not participating directly in the food trade. Scenario analysis highlights that strategies boosting yields (e.g., advanced irrigation) can increase energy and carbon footprints, while consumption-side measures (diet shifts) reduce footprints but may undermine food sustainability if yields drop. Spatial heterogeneity suggests location-specific interventions. The results underscore the importance of integrating sending, receiving, and spillover systems in policy and management to avoid displacing environmental burdens across regions.

This work provides a first comprehensive assessment of how irrigated agriculture in the NCP affects the food-energy-water-CO2 nexus across sending, receiving, and spillover systems using a metacoupling-LCA framework with scenario analysis. The study demonstrates that while the NCP supports national food sustainability, it does so with unsustainable water use and significant energy and carbon costs, and imposes substantial spillover burdens via the SNWTP on Hubei Province. Policy implications include combining supply-side measures (e.g., deficit irrigation, irrigation technology upgrades where efficient) with demand-side strategies (diet shifts, reducing food waste), and considering relocation or limitation of crop production in severely water-stressed areas. The framework and insights are applicable to other regions facing similar challenges. Future research should expand to include household-level dynamics, broader adaptation strategies (population growth, investment, technology improvements, natural disasters), alternative technologies (e.g., gravity-based irrigation), robust water accounting, irrigator incentives, and broader socioeconomic outcomes (poverty, equity, health, well-being) to inform comprehensive sustainable development strategies.

Analyses could not be conducted at the household level due to data limitations. The set of 15 scenarios, although covering multiple environmental and socioeconomic factors, may not capture the full complexity of interactions in irrigated agriculture. LCA-based results carry uncertainties from data and methodological assumptions, though data quality assessment and Monte Carlo analysis indicated uncertainties between 3–6%. Additional factors such as detailed behavioral responses, policy incentives, and unforeseen events (e.g., disasters) were not explicitly modeled.