Multi-Scale Investigation of Water-Energy-Food Nexus

Water, energy and food (WEF) are among essentials to meet the basic human needs and ensure economic and social development. Globally, the demand for WEF rapidly increases while billions of people are still lacking access to these needs. The main drivers behind increased demand for WEF are population growth, urbanization, economic growth and climate change. It may also be driven by changes in demography, technological developments and diet preferences. To achieve a sustainable supply and effectively manage the demand for WEF, complex interactions between WEF (nexus) need to be understood. Traditionally, WEF have been studied and managed separately with a minimal focus on their interactions. The primary objective of this study is to investigate WEF nexus at different scales. A bottom-up approach has been employed to develop a system-dynamics based model to capture the interactions between WEF at end-use level at a household scale. Additionally, a city scale model has been developed to quantify WEF implications for agricultural, commercial and industrial sectors. The household level model is then integrated with the city scale model to estimate WEF demand and the generated organic waste and wastewater quantities. The integrated model investigates the impact of several variables on WEF: human bahaviour, diet, household income, family size, seasonal variability, population size, GDP, crop type and land-use for agriculture. The integrated model is based on a detailed survey of 407 households conducted to investigate WEF over winter and summer season for the city of Duhok, Iraq. The city is chosen as a case study due to the rapid population growth, considerable urbanization, changes in land-use pattern and shifting climate trends toward longer summer duration. These put an additional pressure on WEF demand in the city. The collected data of WEF and household characteristics (demographic and socio-economic) have been intensively analysed to provide a better understanding for the factors influencing WEF consumption. The surveyed data was used to develop statistical regression models for estimating demand as a function of household characteristics using stepwise-multiple-linear and evolutionary polynomial regression techniques. The integrated WEF model was subjected to sensitivity analysis and uncertainty assessment. A comparison of the model simulation results were made with the historical data. The model results show a good agreement with the historical data. The WEF model is then applied to assess the risk and resilience of WEF systems under the impact of seasonal climate variability (i.e., increase/decrease in the number of summer days). In order to decrease the risk of not meeting per capita demand for WEF and increase the resilience of system for providing per capita demand for WEF, a number of demand management strategies have been investigated in water and energy systems under the impact of seasonal variability. The results show that using recycled greywater for non-potable application in Duhok water system is the most efficient strategy but it increases the energy demand. Additionally, anaerobic digestion of food waste and wastewater sludge for energy recovery can increase the resilience of Duhok energy system. Finally, the impact, of Global Scenario Group (GSG) scenarios (Market Forces, Fortress World, Great Transition and Policy Reform) on the WEF consumption and resulting implications, has been investigated using the WEF model. The results suggest that the Fortress World scenario (an authoritarian response to the threat of breakdown) has the highest impact on WEF consumption. In the Great Transition scenario, WEF consumption would be the lowest. The model results suggest that the food-related water consumption is the highest in the Policy Reform scenario