Approach for optimizing the water-land-food-energy nexus in agroforestry systems under climate change

Highlights

• Food, energy, water and land resources in agroforestry systems are inseparable and are impacted by climate change.

• A cooperative optimization model is proposed to manage water-land-food-energy nexus (WLFEN) and cope with climate change.

• Resources reallocation in WLFEN improve synergy of resource use efficiency, economic benefit and environmental impacts.

• Inner linkage and synergy exist among resources in WLFEN in agroforestry systems and they are sensitive to climate change.

• We put forward a quantitative way to assist managing agricultural resources sustainability in a change environment.

Abstract

CONTEXT

Agroforestry systems are widely promoted for their economic and environmental benefits. Food, energy, water and land resources in agroforestry systems are inextricably intertwined and expected to be severely impacted by climate change. Socioeconomic development and increasing populations have posed unique challenges for meeting the demand for food, energy, water and land, and the challenge will become more pressing under projected resource shortages and eco-environmental deterioration. Thus, a method of optimizing and sustainably managing the water-land-food-energy nexus in agroforestry systems under climate change must be developed.

OBJECTIVE

This paper develops an optimization model framework for the sustainable management of limited water-land-food-energy resources in agroforestry systems under climate change. The aims are to (1) quantify the interactions and feedbacks within water, land, food and energy subsystems; (2) provide trade-offs among water and energy utilization efficiency, economic benefits and environmental protection in agroforestry systems; and (3) generate optimal policy options among water and land resources for different crops and woodlands in different regions under different climate change patterns.

METHODS

The model framework is based on multiobjective fractional programming, and compromise programming is used to solve it. Climate change patterns are obtained from atmospheric circulation models and representative concentration pathways. The above aims are investigated through an actual nexus management problem in northeast China. Spatiotemporal meteorological and report-based databases, life cycle assessments, Pearson correlation analyses, data envelopment analyses and analytic hierarchy processes are integrated to realize practical application.

RESULTS AND CONCLUSIONS

The results show that climate variation will change the water and land allocation patterns and these changes will be more pronounced for major grain-producing areas. The optimized water allocation decreased (especially for rice, e.g., the optimal average value of the irrigation quota of rice was 4226 m³/ha, while the corresponding actual irrigation requirement of rice was [4200–7200] m³/ha) to improve the water use efficiency, and surface water allocation accounted for two-thirds. Maize had the largest planting area, although planting soybean generated the most greenhouse gases (greenhouse gas emissions from field activities for rice, maize, and soybean were 43.46%, 84.06% and 91.16%, respectively); However, these gases can be absorbed by forests. The model improved the harmonious degree of the resource-economy-environment system from 0.24 to 0.56 after optimization.

SIGNIFICANCES

Integrated models contribute to the sustainable management of water, food, energy and land resources and can consider the complex dynamics under climate change. It can be used as a general model and extended to other agroforestry systems that show inefficient agricultural production.

Introduction

Water, food, land, and energy are basic needs for maintaining life and ensuring sustainable socioeconomic development, and their relationships are complex and inseparable (Finley and Seiber, 2014; Pahl-Wostl, 2019). Increasing natural and anthropogenic pressures have increased the difficulty of continuing to meet the growing needs for water, food and energy in a sustainable manner (Tian et al., 2018). Reports have estimated that by 2030, human demand for water will increase by 40%, energy demand will increase by 50%, and food demand will increase by 35% compared to the data published by the United States National Intelligence Council for 2012 (Endo et al., 2017). The water-food-energy (WFE) nexus, which was first proposed in 2011 in Bonn, Germany, is a conceptual tool for sustainable development (Biggs et al., 2015; Yu et al., 2020). The WFE nexus is conducive to solving resource allocation problems, alleviating resource shortages and improving comprehensive resource management and decision-making that link water, food and energy.

In agricultural systems, water, food, energy and land are inextricably interrelated, and shortages and irrational use of water, land and energy resources have seriously affected food production, especially in developing countries (Karabulut et al., 2018; Li et al., 2019b). Crop planting and forestry are two major sectors of agricultural systems that consume water, land and energy resources together, with water used for farmland and woodland irrigation and food and energy production; water and energy used for food production; and energy used for pumping and drainage and for crop cultivation and harvest. Crops and trees grow on land, and their wastes are used as raw material to produce biomass energy (Li et al., 2021; Timko et al., 2018). Water, land and energy resources are interrelated in crop planting and forestry, which requires the establishment of a water-land-food-energy nexus (WLFEN) for agroforestry systems and the coordinated regulation of water, energy and land resources to guarantee food security and resist environmental changes.

Recent research has reported on the management of water, food, land and energy resources in crop planting or forestry. For example, De Laurentiis et al. (2016) applied the WFE nexus to balance the growing demand for food and limit production capacity to ensure food security. Fabiani et al. (2020) used the WFE nexus to assess the sustainability of durum wheat production systems in the Mediterranean region of central Italy. Melo et al. (2020) proposed an integrated model framework of water-energy-food-forest to help achieve sustainable development goals (SDGs). These studies emphasized the significance of integrated management of the agricultural WFE nexus. Among the methods of managing the WFE nexus, optimization modeling is advantageous for realizing optimal policies of water, food and energy resources, and it acts as a powerful tool for presenting the optimum system performance. Bazilian et al. (2011) first proposed a comprehensive modeling method to address the WFE nexus and provided a vital theoretical reference for emerging studies focused on the WFE nexus. Current studies have addressed WFE nexus issues using an optimization modeling approach in an agricultural system. For example, Sun et al. (2020) developed a stochastic-fuzzy modeling approach based on the WFE nexus to reflect the relationship between water and power/energy in irrigated agriculture. Li et al. (2019a) developed an integrated optimization model for managing the WFE nexus to balance the economic benefits and carbon emissions of crop farming. Zhang and Vesselinov (2017) provided a multiperiod socioeconomic model to predict WFE demands based on model inputs that represented production costs, socioeconomic demands and environmental impacts. However, most previous studies focused on optimizing the WFE nexus of crop farming in an agricultural system, whereas limited cases have collaboratively regulated water, land and energy resources by establishing WLFEN based optimization modeling in an agroforestry system.

To achieve the achieve United Nations' SDGs, the energy allocated to land and water must be considered. Building upon existing land use conditions, the current global goal of achieving SDGs in agriculture and forestry is to reconcile policies across a region based on regional boundaries and limits (van Noordwijk et al., 2018). In the context of SDGs, the coordinated regulation of water, land and energy resources based on the WLFEN in an agroforestry system should not only focus on economic benefits but also other important goals, such as the associated environmental effects and resource use efficiency (Elagib and Al-Saidi, 2020). Grain production and forestry tend to promote economic benefits at the expense of consuming water, land, electricity, fertilizer, pesticides, and other resources, which will affect the resource use efficiency. The heavy use of resources will lead to water pollution, soil erosion and other environmental matters. These findings highlight the need for a multidimensional and multiobjective optimization modeling framework for agroforestry systems that balances conflicts among improving economic development, environmental protection and resource use efficiency and considers the complexity of the relationship among the components of the WLFEN. The model can contribute to improving people's earnings, thereby relieving poverty, ensuring food security (SDG 1 and SDG 2, details of the related SDGs are shown in supplementary material), improving the environment and promoting the efficient and sustainable use of water, land and energy resources (SDG 6 and SDG7).

In addition, global warming is an inevitable global climate problem. The SDGs are consistent with the Paris Agreement in addressing climate change and require profound changes in policy, technology, society, and business in every country (Sachs et al., 2019). Addressing climate change and its impacts (SDG13) requires transformative action in the food system, including the associated technology, policies, capacity enhancements and finances (Campbell et al., 2018). Mushtaq et al. (2013) highlighted shifts in irrigation technology to improve the water use efficiency and reduce greenhouse gas emissions under climate change. Based on the energy-water-food nexus approach, Maraseni et al. (2021) integrated an analysis of water and resource use under climate change and explored water and land allocation options that do not interfere with food production and economic goals. The coordinated regulation of the main components of the WLFEN has multidimensional and multiobjective characteristics that are significantly affected by climate change. Climate change will lead to uncertainties in temperature, precipitation, solar radiation and other climatic factors, which will affect crop evapotranspiration, crop water demand and food production. The irrigation water demand of forestland is also affected by climate factors. The gross primary productivity (GPP) of woodlands reflects the organic matter stored by vegetation through photosynthesis, which is greatly affected by solar radiation. Climate change has a great impact on the output and ecological environment of agroforestry systems. Thus, determining a method of obtaining coordinated regulation schemes of the main components of the WLFEN that can adapt to climate change is worthy of further exploration.

Therefore, taking agroforestry systems as the research carrier, this study aims to develop a WLFEN based optimization model for the simultaneous allocation of limited water, land and energy resources to achieve the synchronous development of resource use efficiency, economic benefits and environmental side effects, which will promote the sustainable use of water, land and energy resources in agroforestry systems. Considering the impact of climate change on the WLFEN in agroforestry systems, allocation strategies of water, land and energy resources under climate change will be generated. The developed model was applied to Heilongjiang Province in Northeast China to demonstrate its applicability and feasibility. The model can help provide sustainable development strategies for water, land and energy resources in an agroforestry system that are environmentally friendly and present high water and energy use efficiency and high economic benefits.