This study proposed a holistic three-fold scheme that synergistically optimizes the benefits of the Water-Food-Energy (WFE) Nexus by integrating the short/long-term joint operation of a multi-objective reservoir with irrigation ponds in response to urbanization. The three-fold scheme was implemented step by step: (1) optimizing short-term (daily scale) reservoir operation for maximizing hydropower output and final reservoir storage during typhoon seasons; (2) simulating long-term (ten-day scale) water shortage rates in consideration of the availability of irrigation ponds for both agricultural and public sectors during non-typhoon seasons; and (3) promoting the synergistic benefits of the WFE Nexus in a year-round perspective by integrating the short-term optimization and long-term simulation of reservoir operations. The pivotal Shihmen Reservoir and 745 irrigation ponds located in Taoyuan City of Taiwan together with the surrounding urban areas formed the study case. The results indicated that the optimal short-term reservoir operation obtained from the non-dominated sorting genetic algorithm II (NSGA-II) could largely increase hydropower output but just slightly affected water supply. The simulation results of the reservoir coupled with irrigation ponds indicated that such joint operation could significantly reduce agricultural and public water shortage rates by 22.2% and 23.7% in average, respectively, as compared to those of reservoir operation excluding irrigation ponds. The results of year-round short/long-term joint operation showed that water shortage rates could be reduced by 10% at most, the food production rate could be increased by up to 47%, and the hydropower benefit could increase up to 9.33 million USD per year, respectively, in a wet year. Consequently, the proposed methodology could be a viable approach to promoting the synergistic benefits of the WFE Nexus, and the results provided unique insights for stakeholders and policymakers to pursue sustainable urban development plans.

This study is an attempt to fill a knowledge gap in our understanding of WEF nexus, focusing on the effects of direct and indirect resource consumption with a life-cycle approach. In Taiwan, the food subsystem is water-intensive and energy-intensive, consuming 99% of water and energy resources directly to produce food. The water subsystem directly consumes 87.18% of its energy for water production, but indirectly consumes 12.82% for operations to prepare for water production and supply. However, the energy subsystem indirectly consumes 91% of the energy and 83% of the water from operations to prepare for energy generation. Consequently, direct resource consumption in the food subsystem and indirect operations in the energy subsystem cause more environmental impacts than those caused by others. The results highlight that environmental impacts derive from not only direct resource consumption but also preparation and production for resource generation (indirect consumption). There are approximately 28% of environmental impacts derived from indirect resource consumption in WEF nexus. Without considering the indirect resource consumption, we will underestimate the total resource depletion and environmental impacts. This study can help in developing policies for saving water and energy and in enforcing resource security.

Since the Bonn 2011 Conference, the Food-Energy-Water (FEW) nexus has become one of the most popular global research topics. Understanding and addressing the complex interactions between the FEW components is essential for sustainable development. This study proposes an environmental impact minimization model, which considers the FEW nexus under four climate change scenarios, to optimize the spatial distribution of three energy crops (rice, corn, and sugarcane). Life cycle assessment (LCA), linear programming, and a climate change simulation model are integrated to analyze appropriate bioenergy production rates while comparing the benefits of bioenergy with the current renewable energy policy in Taiwan. The major findings of LCA in this study indicate that electricity generation using bio-coal produced from rice straw is very beneficial to the environment. Considering the spatial characteristics of Taiwan, simulations from the spatial optimization model suggested that (a) the rice and corn cultivation areas should be increased in southern Taiwan for bio-coal and bioethanol production, in accordance with the “food and feed priority policy”; and (b) the rice cultivation area should be decreased across Taiwan, based on the “water conservation policy”. In addition, compared to solar power, the development of bioenergy can simultaneously enhance food and energy self-sufficiency.

Water-, energy-, and food (WEF) related practices, such as low impact development (LID), residential solar panels, and rooftop urban agriculture, have been applied to improve urban sustainability and resilience under climate change and urbanization. However, most practices require space. This requirement may result in competition for land. In addition, not all newly built practices benefit the environment from the life cycle perspective. Therefore, this study aims to develop a systematic WEF-related practice planning method to improve urban sustainability and resilience in a limited space. The core method is a multi-objective optimization model that considers the performance and environmental impacts of the selected practices. The assessment was conducted in a densely populated area in Taipei, the capital city of Taiwan, to describe the planning processes and demonstrate the feasibility of the methods. In the Taipei case, five goals were defined: the supply of WEF, the sponge city development target, and the greenhouse gas reduction target. The optimal results of the multi-objective optimization model indicated the closeness of the optimal implementation of WEF-related practices to achieving the goals. The results showed that the optimal arrangement of WEF-related practices could provide water supply benefits and was favorable for developing a sponge city. According to the sensitivities, to achieve urban sustainability and resilience, the priorities in order of importance are as follows: establish a rainwater harvesting system for buildings, encourage the implementation of rooftop photovoltaic systems, and improve the materials and processes used solar panel and bioretention cell production. The systematic planning method provides a quantitative assessment and delivers practical cross-sectoral integrated strategies for decision-making.

Hybrid hydropower and floating photovoltaic power generation has far-reaching effects on the intertwined water, food and energy (WFE) nexus, but the complementary operation is fundamentally challenging especially under high uncertainties of hydro-meteorological conditions. This study proposed an artificial intelligence-based WFE system-overarching solution driven by hybrid hydro-floating photovoltaic power generation for promoting nexus synergies. A multi-objective optimization model grounded upon the Grasshopper Optimization Algorithm was developed to simultaneously maximize hydro-floating photovoltaic power output, the ratio of water storage to reservoir capacity, and the ratio of water supply to water demand. The Shihmen Reservoir watershed and its WFE system in northern Taiwan constituted the case study. The results demonstrated that the proposed optimization model could significantly improve synergistic benefits of the WFE nexus by reaching 13%, 13.3% and 15.1% in water storage, food production and hydro-floating photovoltaic power output, respectively. The optimal tilt angles of floating photovoltaic installation would vary between −11.9° (Summer) and 44.3° (Winter). This study opens up new perspectives on green energy production expansion while stimulating WFE nexus synergies in support of policy-makers with feasible schemes on floating photovoltaic deployment in the interest of social sustainability. In consequence, new niches are exploited for floating photovoltaic deployment and give rise to impact mitigation concerning hydro-meteorological uncertainties on WFE nexus management.

This study uses Taiwan's WEF nexus as a case study to demonstrate how the resource flow and associated environmental impact of the WEF nexus can be assessed as basis for evaluating strategies for promoting the sustainable use of natural resources. In this study, material flow analysis (MFA) and life-cycle assessment (LCA), were combined. The MFA was used to examine the interdependence of the three natural resources, and the LCA was used to evaluate the environmental impacts of the WEF system. The WEF nexus analysis shows that tap water supply, oil refining, the cogeneration of steam and electricity, thermoelectric power plants, irrigation, animal husbandry, and aquaculture are the main interwoven nodes and have the most prominent impact on the three natural resources. When the unit products from the WEF system were determined, LCA was implemented for these products to identify 15 types of environmental impacts. The environmental impacts for the WEF system were then calculated based on the use of unit products. The results of LCA showed that the most prominent impacts are the impact of public electricity on climate change; oil products on ozone depletion and ionizing radiation; tap water on metal depletion; and animal husbandry on terrestrial ecotoxicity. Based on the assessment of the alternative resource management strategies, if both water and energy policies are modified simultaneously, the impact of the overall WEF system on most environmental impact categories could be reduced.

Implementing effective resource management is crucial for urban sustainability. Potential resource management strategies should be assessed under the framework of a resource nexus to avoid problem shifting. The urban metabolism of food, energy, and water is driven by lifestyle, industrial structure, and infrastructure. This study employed material flow analysis to identify resource metabolism through the phases of supply, process, demand, and final sink. The resource intensity of urban activities and the risk of the nexus of resources were quantified to illuminate management strategies. This study investigated the food-energy-water nexus (FEW nexus) for a small and multi-sector island city, Kinmen, and found that the nexus risk of water for food is the highest. Water and energy consumption have excessive loads on resource metabolism in a multi-sector city, and the main demand sectors increase the nexus risk in water for food. The results indicated that higher risk results from higher resource consumption intensity, particularly in areas of economic growth. Resource management of the FEW nexus needs the best tradeoff strategy to meet the goals of urban metabolism sustainability. The risk assessment framework can support the design of optimal resource management strategies to pursue urban sustainability. Consequently, given the limitations of water treatment technology, the impact of energy risk mitigation is poor (below 4% of energy risk in 2015) and the energy risk will continue to increase (by about 10% based on the economic activity). As a result, imported water is the best tradeoff strategy to meet the FEW nexus safety for Kinmen City as a low-resource and sightseeing activity area.

The urban food garden is an interesting natural solution to the need to develop sponge cities structured and designed to absorb and capture rain water for reducing flooding, worldwide. This study applied a storm water management model and field experiments to investigate properties of the garden substrates. Taipei City was taken as a case study as the Taiwan government has promoted urban food garden projects since 2015. The urban food garden in Taipei has established a cultivable area of 197,168 m², 64,026 m² (32.5%) of which is designated as green-roof gardens and the rest as domestic gardens. Four substrate mixtures were found to have infiltration rates positively related to their soil water content. Substrate 1 had the highest infiltration rate (6.47 × 10⁻⁵ m/s) and soil water content (281%) when vegetation grows in limited containers. In 2019, the total water retention capacity of the urban food garden in Taipei City was 50,550.7 m³. This means that 1 m² of the urban food garden in Taipei retained 256.4 kg of water. Considering climatic conditions, the water retention capacity of the green-roof gardens in Taipei ranges from 28.2% to 41.0%. During short-term high-density rainfall events, the green-roof gardens were found to be more efficient in reducing the runoff volume, whereas during long-term high-density rainfall events, they were found to be more efficient in reducing the runoff peak flow duration (~20 mins) compared with concrete surfaces. This study proved that establishing the urban food garden contributes to increasing the water retention capacity and reducing the volume of surface runoff and the duration of runoff peak flow in prevention of flood disasters.