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

Ensuring food security for a growing global population amidst resource constraints is a major challenge. Food production consumes significant water, energy, and fertilizers, contributing to water scarcity, global warming, and pollution. The interconnectedness of food, energy, water, and CO2 emissions (the nexus) necessitates a systems approach to sustainable development. While research exists on the environmental impacts of food production and trade, particularly irrigated agriculture, systematic quantitative analyses of its effects on the food-energy-water-CO2 nexus across interconnected systems are lacking. This study addresses this gap by analyzing the impacts of irrigated agriculture in China, a country facing significant environmental challenges, including water scarcity and high CO2 emissions. The focus is on the North China Plain (NCP), a major food production region relying heavily on irrigation, and its interaction with other regions through food trade and the South-to-North Water Transfer Project (SNWTP). The metacoupling framework, which considers interconnectedness within and across systems, guides the analysis. The study aims to understand the environmental burdens associated with irrigated agriculture in the NCP, the impacts of various factors on the food-energy-water-CO2 nexus, and the spillover effects on regions like Hubei Province, which supplies water to the NCP via the SNWTP. The findings are expected to inform strategies for sustainable food trade and environmental conservation in China and other regions facing similar challenges.

Existing literature highlights the significant environmental impacts of food production and trade, with irrigated agriculture being particularly impactful. Studies have explored the environmental footprints of specific crops and regions, but a comprehensive and quantitative analysis of the food-energy-water-CO2 nexus across interconnected systems is lacking. Research on the metacoupling framework demonstrates the interconnectedness of socio-economic and environmental interactions within and across geographical boundaries, emphasizing the often-overlooked impacts on spillover systems. Several studies have investigated the water-food-energy nexus in various contexts. The impacts of irrigated agriculture on water resources and greenhouse gas emissions have also been studied extensively, but seldom have studies combined these factors across different regions of a nation, particularly using the metacoupling framework. This paper aims to fill this research gap by quantifying the water, energy and carbon footprints and assessing sustainability across sending, receiving and spillover systems, contributing significantly to the understanding of the complex interactions within the food-energy-water-CO2 nexus.

This study employed a multi-faceted methodology combining life cycle assessment (LCA), model scenarios, and the metacoupling framework. Data were collected from various sources, including meteorological data, agricultural data at the county level, crop evapotranspiration measurements, and data on the SNWTP. LCA was performed according to ISO 14040 & ISO 14067 standards, assessing environmental impacts across five stages of agricultural operations: tillage, sowing, irrigation, fertilization, and harvest. Water footprint calculations considered green, blue, and grey water footprints. A novel approach to calculating water consumption, based on the crop water production function (CWPF), was developed and validated against conventional methods, demonstrating improved accuracy. The CWPF method accounted for the relationship between water use and crop production, considering factors like photosynthetically active radiation and effective accumulated temperature. Fifteen scenarios were constructed (Table 1) to simulate the impacts of various factors, including climate change, irrigation technologies, cropping systems, and dietary changes. The South-to-North Water Transfer Project (SNWTP) was analyzed through a hybrid EIO-LCA method, quantifying CO2 emissions and energy footprint across its life cycle. Spatial variations in environmental impacts were mapped using ArcGIS software. Data quality was assessed using a data quality index (DQI) method, and Monte Carlo simulations were conducted to assess uncertainty. The metacoupling framework categorized systems: the NCP (food-sending), the rest of China (food-receiving), and Hubei Province (spillover). Indicators for water and food sustainability were defined and calculated. Water sustainability was assessed as the ratio of total available water for agricultural use to total water consumption, while food sustainability was assessed as the ratio of actual crop production to the sustainable production needed for national food security. All statistical analyses were performed using Stata 13. The framework integrated AquaCrop model, which predicts crop yield and water requirement, as well as a newly constructed model to account for the energy footprint and CO2 emissions of crop production and water transfers across the studied regions.

The study revealed significant findings regarding the environmental impacts of irrigated agriculture in the NCP and its broader implications. Firstly, all counties in the NCP exhibited unsustainable water use, with total water consumption exceeding renewable water resources by over four times in 2010. While the NCP met its share of national food security, this came at a high environmental cost. Secondly, model scenarios showed substantial variations in water, energy, and carbon footprints across counties within the NCP under various conditions (climate change, irrigation technology, cropping systems, dietary changes, and water transfers via the SNWTP) (Figure 2). Some scenarios, particularly those involving significant dietary changes and improved irrigation techniques, showed substantial improvements in water sustainability, but at the cost of reduced crop yields and potential food insecurity. Others, particularly those incorporating climate change impacts and reduced irrigation, demonstrated worsening of water and food sustainability. Figure 3 illustrates the considerable spatial heterogeneity of water, energy, and carbon footprints across NCP counties. Thirdly, the spillover system (Hubei Province), despite not being directly involved in food trade with the NCP, experienced substantial land (310 km2) and water (9.5 billion m3 annually) losses due to the SNWTP (Figure 1 and Figure 4). The SNWTP also incurred significant CO2 emissions (approximately 3.1 million tons) and energy footprint. The analysis of the SNWTP highlighted considerable carbon and energy footprints at each stage of its lifecycle (material production, transportation, construction and operation), emphasizing the indirect environmental costs of water transfer for agricultural purposes.

The findings highlight the trade-offs between food security and environmental sustainability. While the NCP's food production is crucial for national food security, its unsustainable water consumption poses a serious concern. The spatial heterogeneity in environmental impacts underscores the need for location-specific policies and interventions. The substantial environmental burdens on Hubei Province, a spillover system, emphasizes the importance of considering indirect impacts and the limitations of focusing solely on the sending and receiving systems. The results advocate for a shift away from solely supply-side management (increasing water use, energy consumption, and CO2 emissions) towards integrated supply-side and consumption-side management. Strategies like deficit irrigation and dietary shifts towards less resource-intensive crops can help mitigate environmental impacts. This study emphasizes the crucial role of integrated assessments like metacoupling to comprehensively evaluate the complex interactions within the food-energy-water-CO2 nexus. The complex interactions between different sectors and across geographical boundaries (metacoupling) should be incorporated into policy-making to avoid unintended consequences.

This study provides a novel, comprehensive analysis of the impacts of irrigated agriculture on the food-energy-water-CO2 nexus across metacoupled systems in China. It reveals the unsustainable water use in the NCP despite its critical role in national food security, and the substantial environmental burdens imposed on spillover systems like Hubei Province. The findings advocate for integrated policies that consider both supply-side and consumption-side management, incorporating location-specific strategies to address spatial heterogeneity. Future research should explore a broader range of adaptation strategies, incorporate socioeconomic impacts, and investigate the performance of alternative irrigation technologies.

This study acknowledges several limitations. Data limitations prevented analyses at the household level. While the scenarios considered various factors, they may not fully capture the complexity of real-world interactions. The focus on environmental impacts, while comprehensive, did not include socioeconomic impacts like poverty or social equity. Future research could expand the scope to address these gaps and further enhance the understanding of the interplay between environmental and socioeconomic aspects of food production and water management.