Depending on the depth of the deposit, oil sands are extracted using two different methods―surface mining and in situ drilling . In situ technology requires less water than surface mining . Bitumen from mined oil sands is a low-quality product that needs to be upgraded through a water-demanding process into synthetic crude oil before being delivered to refineries . Shale oil and gas extraction is performed through horizontal drilling and hydraulic fracturing, technologies that require a lower amount of water than other fossil fuels. However, shale oil extraction requires a large upfront use of water over a few days, after which oil is produced over several months . Thus, intensive water withdrawals over a short period of time can induce or enhance local water stress. By adopting a hydrologic perspective that considers water availability and demand together, Rosa et al., 2018 presented a global analysis of the impact of shale oil and gas extraction on water resources, 25 liter pot particularly on irrigated crop production. Using a water balance analysis, Rosa et al., 2018 found that 31–44% of the world’s shale deposits are located in areas where water stress would either emerge or be exacerbated as a result of unconventional oil and gas extraction from shale rocks. This analysis is an example of how research can analyze all the three dimensions of the FEW nexus using geospatial data-driven analyses.
Results from these studies can be used by decision makers and local communities to better understand the water and food security implications of energy systems.A small volume of water is required during the drilling and cementing phases. Interestingly, unconventional gas production from shale gas requires the same amount of water as shale oil wells drilled in the same area . However, energy production from shale oil has a lower water footprint than energy from shale gas because of the higher energetic content of oil. Unconventional gas can also be produced from coal bed methane. In this case, deep coal seams undevelopable for mining operations are drilled to extract the natural gas that is absorbed by the organic material in the coal formation. Coal bed methane has a low water footprint and releases substantial volumes of produced water that, if treated, can be recirculated into the water cycle.Coal has not only high GHG emissions per unit of energy produced but also a high water cost . The amount of water used for coal mining varies between underground and surface mines. Water requirements increase as the coal mine operations move deeper underground. An increasing trend in coal mining operations is to wash coal, a process that requires about 3.79–7.58 L/GJ . Coal washing is accomplished by density separation or froth floatation to separate mined coal ore from a mixture of materials . This process aims to improve combustion efficiency to meet environmental standards by reducing sulfur and particulate emission during combustion .
Water can also be used to transport coal as a slurry through pipelines . In an attempt to curb the increasing atmospheric CO2 concentrations, recent energy policies have mandated a certain degree of reliance on renewable energy sources as alternatives to fossil fuels . Thus, gasoline and diesel are now commonly blended with bio-ethanol and bio-diesel. These bio-fuels can be obtained from a variety of crops, including food crops , cellulose-rich crop residues , and algae . To date , the bio-fuels that are commonly used are of the first generation. Bioethanol is mainly made with maize in the United States and sugarcane in Brazil, whereas bio-diesel is produced using vegetable oil . Bioethanol consumption is for most part domestic, and at leastone third of the global bio-diesel is available through international trade, mostly associated with palm oil from Indonesia and Malaysia . The water used for bio-fuels strongly varies with crop type, geographic location, climate, and soil . First-generation bio-fuels have a much higher water footprint than fossil fuels and therefore compete with the food system directly and indirectly . The competition of bio-fuels with food production explains the heated debate on how bio-energy production competes with the food system and the appropriateness of using food crops to fill fuel tanks instead of feeding the poor . Rulli et al. found, however, that to date, only about 4% of the global energy consumption by the transport sector and 0.2% of global energy use in all sectors is utilized for bio-fuels. For the year 2000, bio-fuel production accounted for about 2–3% of the global land and water used for agriculture .
In 2007, bio-fuel production accounted for about 2% of the global production of inorganic phosphorus fertilizer . Second- and third-generation bio-fuels do not compete with food production because they do not rely on biomass that could otherwise be used for food, and they consume relatively small amounts of water .The water footprint of fossil fuels is typically calculated by accounting only for the water used for oil or gas extraction and processing without considering the fact that these hydrocarbons result from the transformation of ancient plant biomass over geological time . Millions of years ago the growth of that biomass was associated with the transpiration of ancient water, similar to the way today’s bio-fuel production entails the consumptive use of the huge amounts of water . For any agricultural commodity , the water consumed in transpiration is the major contributor to the water footprint of fossil fuels. The main difference, in this case, is that the water used for transpiration is ancient water. The omission of ancient water from the calculation of the water footprint of fossil fuels explains the big gap between the water footprint of fossil fuels and bio-fuels . The ancient water component of the water footprint of fossil fuels is difficult to estimate because that water was transpired millions of years ago by plant species and under climate conditions that do not exist anymore and are not known to us. It is possible, however, to estimate the amount of water that it would take today to replace the “burning” of ancient water with present water by shifting from fossil fuels to present biomass . To meet today’s fossil energy need , a consumptive use of water would be close to 7.39 × 1013 m3 year, which is order of magnitude greater than the water used for extraction and processing that is usually accounted for in water footprint calculations of fossil fuels . Thus,to meet its energy needs, humanity is using an amount of ancient water of the same order of magnitude as the annual evapotranspiration from all terrestrial ecosystems . In other words, the energy that is powering industrial societies relies on water from a geological past . Likewise, the use of fossil fuels is relying on past sunlight and land , allowing industrial societies to have access to an unprecedented amount of energy that cannot be replaced with present-day biomass because of constraints imposed by the water cycle and land availability . These findings highlight the need for nonfuel-based sources of renewable energy as future substitutes for fossil fuels.The discussion of ancient water presented in the previous section highlights some limitations in the calculations of the water footprint of fossil fuels. Although the water footprint of bio-fuels and food products accounts for the water used their production, for fossil fuels, the water footprint accounts for the actual water needed in extraction and processing, neglecting the ancient water used millions of years ago . Moreover, previous works have assessed the water footprint of energy production and power generation from the life cycle analysis perspective without considering the impacts on local water resources . In analyses of the hydrologic impacts of fossil fuel production,raspberry cultivation pot an approach that looks at the total water used for extraction and processing may be misleading because these two water needs are typically met with water resources available in two different locations . LCA scientists typically focus on a comprehensive accounting of all water costs associated with production and processing, regardless of where the water comes from. Therefore, there is the need for a more hydrologic-based approach as an alternative to classic LCA calculations of the water footprint .Thermal power generation accounts for 70% of world power generation . Current technologies used for thermoelectric power plants are based on a steam Rankine cycle and heavily rely on water. In these systems, a cooling fluid is needed to cool and condensate the outlet steam of the expanders. In a thermoelectric power plant, water is heated to produce the steam needed to spin the turbines that generate electricity. Thermodynamic limits require cooling the steam into water before it can be reheated to produce steam again. Surface water from a nearby water body typically is used as a refrigerating fluid because of its availability and efficient heat transfer properties.
For this reason, thermoelectric power plants are built close to rivers, lakes, and seas. The volumes of water withdrawn for thermal power generation are staggering. For example, in the United States thermoelectric power plants account for 40% of total freshwater withdrawals and 4% of freshwater consumption . Power plants built along the coast can reduce the use of freshwater and limit the exposure to water stress. However, seawater is more corrosive and requires more resistant materials and higher capital costs . Nuclear power has the highest water consumption among thermoelectric technologies . Water is needed not only to cool the exhaust steam but also to control the temperature of the fission process of uranium. Additionally, uranium mining and processing requires substantial amounts of water . Coal and natural gas-fired power plants, as well as refineries, can be retrofitted with a carbon capture unit . Although carbon capture and storage is a promising technology to limit the climate change impacts of energy production by reducing CO2 emissions from fossil fuels, the actual technology is based on absorption capture units, which rely on large volumes of water to separate CO2 from the flue gas .Energy is used for multiple food system activities, including the operation of farm machinery and the processing, packaging, transporting, refrigerating, and preparing of food . As one example, the U.S. Department of Agriculture estimated that overall food-related energy use in the United States represented 16% of the Nation’s total energy budget . The energy use involved in the food system therefore to some degree links food systems to GHG emissions. Food systems contribute between 19% and 29% of total global anthropogenic GHG emissions, but direct emissions from agricultural production and indirect emissions resulting from land use change contribute much more to total emissions than other food system activities . Even before the food production stage, energy use is required in the production of fertilizers and pesticides; for example, industrial ammonia synthesis using the HaberBosch process for N fertilizer manufacturing uses greater than 1% of energy production worldwide because of its reliance on high temperature and high pressure . Although food is increasingly transported across vast distances, a life cycle assessment of U.S. foods by Weber and Matthews found that transportation represented just 11% of total food-related GHG emissions, meaning that food choice had a higher relative impact on the reduction of overall emissions than the sourcing of local foods to reduce transportation emissions. One of the most obvious ways in which food is linked to energy is the use of food crops as feed stock for bio-fuel production . There is a myriad of cases where the water needs of the energy and food sectors strongly interact with one another through their competition for land and water . As a result, energy prices can also be linked to food prices because of the increased cost of agricultural production and transportation , which was observed particularly with the growing demand for first-generation bio-fuels as a result of higher oil prices in the 2000s . The links between food and first-generation bio-fuels are further discussed in the following section.The production of bio-fuels is one of the more prominent examples of connections between food and energy markets that has raised concerns about diverting resources from one product to the production of another product , which can generate higher returns. These dynamics are further complicated by agricultural subsidies, tariffs, incentives for renewable energy, and opportunities associated with international land investments for agribusiness corporations.