The role of climate in the Water-Energy-Food Nexus considering CO2 emissions, Insights from semiarid regions
Thesis event information
Date and time of the thesis defence
Place of the thesis defence
L1 Pohjanmaa Hall, Linnanmaa Campus
Topic of the dissertation
The role of climate in the Water-Energy-Food Nexus considering CO2 emissions, Insights from semiarid regions
Doctoral candidate
Doctor of Science (Technology) Marzieh Hassanzadeh Saray
Faculty and unit
University of Oulu Graduate School, Faculty of Technology, Water, Energy and Environmental Engineering
Subject of study
Environmental Engineering
Opponent
Associate Professor Abbas Roozbahani , Norwegian University of Life Sciences, Norway
Custos
Professor Ali Torabi Haghighi, University of Oulu
How climate affects water, energy, food production and CO₂ emissions in dry regions
This doctoral research focuses on the connections between water, energy, food production and carbon dioxide emissions in agriculture. These four elements are closely linked. Producing food requires water and energy, while the use of fuels, electricity, fertilizers, machinery and irrigation can also lead to greenhouse gas emissions. In regions where water is limited and agriculture depends heavily on irrigation, these connections become especially important. The main purpose of this research was therefore to understand how agricultural production can be managed in a way that balances food production, resource use, economic performance and environmental impacts.
The research was carried out using two case-study areas in Iran. The first was Sahand Agro-Industry in northwest Iran, where detailed farm-level information was available for seven crops: alfalfa, barley, silage corn, potato, rapeseed, sugar beet and wheat. The second case study was the Zayandeh-Rud River Basin in central Iran, where agriculture uses a large share of the available water resources and is also an important electricity consumer. Using these two different scales made it possible to examine both detailed farm-level performance and broader resource-management challenges.
The study compared crops using several types of information. These included water consumption, energy consumption, crop yield, economic return and CO₂ emissions. Different indicators were calculated to show how efficiently each crop used water and energy and how much production or economic value was obtained from these resources. These indicators were then combined into broader Water-Energy-Food Nexus indices. The purpose of these indices was to provide a more complete picture of crop performance instead of evaluating only one factor at a time. In some parts of the research, greenhouse gas emissions were also added to the Nexus assessment so that environmental performance could be considered together with water, energy and food production.
An important part of the research was the analysis of energy use in agriculture. The study considered different energy inputs, including diesel fuel, electricity, machinery, fertilizers, irrigation, seeds and other agricultural inputs. The results showed that energy use varied considerably between crops. Potato had the highest total energy input, while barley had the lowest. Sugar beet, however, produced the highest energy output and showed the highest energy-use efficiency among the studied crops. Another major finding was the strong dependence of the agricultural system on non-renewable energy. Depending on the crop, most of the total energy input came from non-renewable sources, especially diesel fuel, fertilizers and machinery. This shows that reducing dependence on fossil-energy inputs could be important for improving the sustainability of agricultural production.
The study also showed that low resource use does not automatically mean high efficiency. For example, alfalfa used the most water, while barley used the least. However, silage corn achieved the highest water and energy productivity. This means that crop performance depends not only on how much water or energy is used, but also on how much useful output is produced from those resources. Rapeseed showed high water economic productivity, while other crops performed better in terms of energy or total production. These differences demonstrate why a single indicator cannot fully describe whether a crop is sustainable.
When the different resource and productivity indicators were combined into the Water-Energy-Food Nexus Index, clear differences appeared between crops. Silage corn had one of the highest overall Nexus performances, while potato had the lowest. This was an important result because potato can produce relatively high yields, but it also requires large amounts of water, energy and other inputs. The results therefore showed that high agricultural production alone does not necessarily mean good overall sustainability. When greenhouse gas performance was included through the WEFG approach, the scores generally decreased and the ranking of some crops changed. This demonstrated that including emissions can change how agricultural performance is interpreted.
CO₂ emissions were another central part of the study. Emissions were estimated from the main agricultural inputs, including diesel, electricity, machinery, fertilizers, biocides, seeds and irrigation-related energy. The results showed large differences between crops. Potato had the highest total CO₂ emissions per hectare, while barley had the lowest. Diesel fuel and nitrogen fertilizer were among the most important contributors to emissions. This shows the close link between energy-intensive farming practices and the carbon footprint of agricultural production. However, the study also found that total emissions per hectare do not tell the whole story. When emissions were calculated per kilogram of crop produced, the ranking changed significantly. Silage corn had the lowest CO₂ emissions per kilogram of product because of its high yield, while rapeseed had the highest emission intensity. The analysis also showed that increasing crop yield can reduce emissions per kilogram of product if the level of inputs remains similar. For example, the calculations indicated that a 20% increase in crop yield could reduce CO₂ emissions per kilogram of product by about 16.7%. This finding highlights the importance of considering both total emissions and production efficiency when evaluating environmental performance.
Another major part of the research was the use of optimization methods to compare different agricultural strategies. The purpose of optimization was not simply to identify the crop with the highest yield or the lowest emissions, but to understand what happens when several goals are considered at the same time. In one analysis, the model first tested a strategy that maximized the Water-Energy-Food Nexus performance and another strategy that minimized CO₂ emissions. These two strategies produced very different results. Maximizing WEF performance resulted in higher food production, but also greater water and energy use and higher emissions. In contrast, minimizing CO₂ emissions reduced resource use and environmental pressure, but food production fell substantially.
A balanced solution was therefore developed to find a compromise between production and environmental performance. This solution did not achieve the highest food production or the lowest possible emissions, but it provided an intermediate outcome between the two extremes. The results showed that decisions based on a single objective can easily create negative effects elsewhere in the system. For example, reducing emissions as much as possible can lower food production, while maximizing production can increase pressure on water, energy and the environment.
The research was then extended to a broader multi-objective Water-Energy-Food-Carbon framework. Five different goals were compared: minimizing water use, minimizing energy use, maximizing food production, maximizing profit and minimizing CO₂ emissions. The results again showed clear conflicts between these goals. Strategies that minimized water, energy and emissions generally favored crops such as barley, rapeseed and wheat. In contrast, strategies that maximized food production or profit tended to favor crops such as alfalfa, sugar beet and potato, which require more resources and can also create higher environmental impacts.
The integrated WEFC optimization provided a more balanced cropping pattern. In the optimal solution, the largest areas were allocated to wheat, rapeseed and barley, with a smaller area for sugar beet. Crops with high production or profit potential were not always selected because of their relatively high water use, energy demand or CO₂ emissions. This result clearly demonstrates the central message of the thesis: there is no single crop or single management objective that provides the best outcome in every respect. Sustainable agricultural planning requires balancing several competing goals at the same time.
The main contribution of this research is the explicit integration of anthropogenic CO₂ emissions into the analysis of water, energy and food systems, especially at farm scale. This makes it possible to study how changes in resource use can influence productivity, emissions and economic performance together. The work also shows how integrated Nexus-based methods can reveal trade-offs and possible co-benefits that may be missed when water, energy, food or emissions are studied separately. The inclusion of detailed energy analysis further improves understanding of how agricultural resource use contributes to environmental impacts.
Overall, the findings show that agricultural sustainability cannot be achieved by maximizing only one target. Producing more food, using less water, reducing energy consumption, increasing profit and lowering CO₂ emissions are all important, but they often conflict with each other. The Water-Energy-Food-CO₂ Nexus provides a useful framework for understanding these interactions and identifying more balanced solutions. The results can support farmers, researchers and decision-makers in improving land-use planning, resource efficiency and environmental performance in regions where water, energy and agricultural resources are limited.
Future research should focus on bringing these approaches closer to practical agricultural decision-making. Better data from digital monitoring, precision agriculture and remote sensing could improve the accuracy of Nexus assessments. Climate-change scenarios should also be more explicitly included to understand how future conditions may affect water availability, energy demand, crop productivity and resilience. Greater use of renewable energy and more advanced multi-objective optimization models could further reduce environmental impacts. Finally, stronger links between research, policy and local stakeholders are needed to bridge the gap between Nexus theory and real-world agricultural management.
The research was carried out using two case-study areas in Iran. The first was Sahand Agro-Industry in northwest Iran, where detailed farm-level information was available for seven crops: alfalfa, barley, silage corn, potato, rapeseed, sugar beet and wheat. The second case study was the Zayandeh-Rud River Basin in central Iran, where agriculture uses a large share of the available water resources and is also an important electricity consumer. Using these two different scales made it possible to examine both detailed farm-level performance and broader resource-management challenges.
The study compared crops using several types of information. These included water consumption, energy consumption, crop yield, economic return and CO₂ emissions. Different indicators were calculated to show how efficiently each crop used water and energy and how much production or economic value was obtained from these resources. These indicators were then combined into broader Water-Energy-Food Nexus indices. The purpose of these indices was to provide a more complete picture of crop performance instead of evaluating only one factor at a time. In some parts of the research, greenhouse gas emissions were also added to the Nexus assessment so that environmental performance could be considered together with water, energy and food production.
An important part of the research was the analysis of energy use in agriculture. The study considered different energy inputs, including diesel fuel, electricity, machinery, fertilizers, irrigation, seeds and other agricultural inputs. The results showed that energy use varied considerably between crops. Potato had the highest total energy input, while barley had the lowest. Sugar beet, however, produced the highest energy output and showed the highest energy-use efficiency among the studied crops. Another major finding was the strong dependence of the agricultural system on non-renewable energy. Depending on the crop, most of the total energy input came from non-renewable sources, especially diesel fuel, fertilizers and machinery. This shows that reducing dependence on fossil-energy inputs could be important for improving the sustainability of agricultural production.
The study also showed that low resource use does not automatically mean high efficiency. For example, alfalfa used the most water, while barley used the least. However, silage corn achieved the highest water and energy productivity. This means that crop performance depends not only on how much water or energy is used, but also on how much useful output is produced from those resources. Rapeseed showed high water economic productivity, while other crops performed better in terms of energy or total production. These differences demonstrate why a single indicator cannot fully describe whether a crop is sustainable.
When the different resource and productivity indicators were combined into the Water-Energy-Food Nexus Index, clear differences appeared between crops. Silage corn had one of the highest overall Nexus performances, while potato had the lowest. This was an important result because potato can produce relatively high yields, but it also requires large amounts of water, energy and other inputs. The results therefore showed that high agricultural production alone does not necessarily mean good overall sustainability. When greenhouse gas performance was included through the WEFG approach, the scores generally decreased and the ranking of some crops changed. This demonstrated that including emissions can change how agricultural performance is interpreted.
CO₂ emissions were another central part of the study. Emissions were estimated from the main agricultural inputs, including diesel, electricity, machinery, fertilizers, biocides, seeds and irrigation-related energy. The results showed large differences between crops. Potato had the highest total CO₂ emissions per hectare, while barley had the lowest. Diesel fuel and nitrogen fertilizer were among the most important contributors to emissions. This shows the close link between energy-intensive farming practices and the carbon footprint of agricultural production. However, the study also found that total emissions per hectare do not tell the whole story. When emissions were calculated per kilogram of crop produced, the ranking changed significantly. Silage corn had the lowest CO₂ emissions per kilogram of product because of its high yield, while rapeseed had the highest emission intensity. The analysis also showed that increasing crop yield can reduce emissions per kilogram of product if the level of inputs remains similar. For example, the calculations indicated that a 20% increase in crop yield could reduce CO₂ emissions per kilogram of product by about 16.7%. This finding highlights the importance of considering both total emissions and production efficiency when evaluating environmental performance.
Another major part of the research was the use of optimization methods to compare different agricultural strategies. The purpose of optimization was not simply to identify the crop with the highest yield or the lowest emissions, but to understand what happens when several goals are considered at the same time. In one analysis, the model first tested a strategy that maximized the Water-Energy-Food Nexus performance and another strategy that minimized CO₂ emissions. These two strategies produced very different results. Maximizing WEF performance resulted in higher food production, but also greater water and energy use and higher emissions. In contrast, minimizing CO₂ emissions reduced resource use and environmental pressure, but food production fell substantially.
A balanced solution was therefore developed to find a compromise between production and environmental performance. This solution did not achieve the highest food production or the lowest possible emissions, but it provided an intermediate outcome between the two extremes. The results showed that decisions based on a single objective can easily create negative effects elsewhere in the system. For example, reducing emissions as much as possible can lower food production, while maximizing production can increase pressure on water, energy and the environment.
The research was then extended to a broader multi-objective Water-Energy-Food-Carbon framework. Five different goals were compared: minimizing water use, minimizing energy use, maximizing food production, maximizing profit and minimizing CO₂ emissions. The results again showed clear conflicts between these goals. Strategies that minimized water, energy and emissions generally favored crops such as barley, rapeseed and wheat. In contrast, strategies that maximized food production or profit tended to favor crops such as alfalfa, sugar beet and potato, which require more resources and can also create higher environmental impacts.
The integrated WEFC optimization provided a more balanced cropping pattern. In the optimal solution, the largest areas were allocated to wheat, rapeseed and barley, with a smaller area for sugar beet. Crops with high production or profit potential were not always selected because of their relatively high water use, energy demand or CO₂ emissions. This result clearly demonstrates the central message of the thesis: there is no single crop or single management objective that provides the best outcome in every respect. Sustainable agricultural planning requires balancing several competing goals at the same time.
The main contribution of this research is the explicit integration of anthropogenic CO₂ emissions into the analysis of water, energy and food systems, especially at farm scale. This makes it possible to study how changes in resource use can influence productivity, emissions and economic performance together. The work also shows how integrated Nexus-based methods can reveal trade-offs and possible co-benefits that may be missed when water, energy, food or emissions are studied separately. The inclusion of detailed energy analysis further improves understanding of how agricultural resource use contributes to environmental impacts.
Overall, the findings show that agricultural sustainability cannot be achieved by maximizing only one target. Producing more food, using less water, reducing energy consumption, increasing profit and lowering CO₂ emissions are all important, but they often conflict with each other. The Water-Energy-Food-CO₂ Nexus provides a useful framework for understanding these interactions and identifying more balanced solutions. The results can support farmers, researchers and decision-makers in improving land-use planning, resource efficiency and environmental performance in regions where water, energy and agricultural resources are limited.
Future research should focus on bringing these approaches closer to practical agricultural decision-making. Better data from digital monitoring, precision agriculture and remote sensing could improve the accuracy of Nexus assessments. Climate-change scenarios should also be more explicitly included to understand how future conditions may affect water availability, energy demand, crop productivity and resilience. Greater use of renewable energy and more advanced multi-objective optimization models could further reduce environmental impacts. Finally, stronger links between research, policy and local stakeholders are needed to bridge the gap between Nexus theory and real-world agricultural management.
Created 23.9.2026 | Updated 25.9.2026