The Sustainable Water-Energy Nexus: Life-Cycle Impacts and Feasibility of Regional Energy and Water Supply Scenarios

Water and energy are critical, interdependent, and regional resources, and effective planning and policies around which sources to use requires combining information on environmental impacts, cost, and availability. Questions around shifting energy and water sources towards more renewable options, as well as the potential role of natural gas from shale formations are under intense discussion. Decisions on these issues will be made in the shadow of climate change, which will both impact and be impacted by energy and water supplies. \ud This work developed a model for calculating the life-cycle environmental impacts of regional energy and water supply scenarios (REWSS). The model was used to discuss future energy pathways in Pennsylvania, future electricity impacts in Brazil, and future water pathways in Arizona. To examine energy in Pennsylvania, this work also developed the first process-based life-cycle assessment (LCA) of shale gas, focusing on greenhouse gas (GHG) emissions, energy consumption, and water consumption. This LCA confirmed results that shale gas is similar to conventional gas in GHG emissions, though potentially has a lower net energy due to a wide range of production rates for wells.\ud Brazil’s electricity-related impacts will rise as development continues. GHG emissions are shown to double by 2020 due to expanded natural gas (NG) and coal usage, with a rise of 390% by 2040 posssible with tropical hydropower reservoirs. While uncertainty around reservoir impacts is large, Brazil’s low GHG emissions intensity and future carbon emissions targets are threatened by likely electricity scenarios.\ud Pennsylvania’s energy-related impacts are likely to hinge on whether NG is used as a replacement for coal, allowing GHG emissions to drop and then plateau at 93% of 2010 values; or as a transition fuel to expanded renewable energy sources, showing a steady decrease to 86% in 2035. Increased use of biofuels will dominate land occupation and may dominate water consumption impacts, depending on irrigation – water consumption for energy rises from 7% to 18% under the base case. \ud Arizona is further from major shale basins, but aims to reduce unsustainable groundwater usage. Desalination by itself will increase annual impacts by at least 2% in all impact categories by 2035, and prioritizing renewable energy sources along with desalination was found to lower GHGs by 1% from BAU, but increase 2035 impacts in all other categories by at least 10% from new construction or operation. \ud In both PA and AZ, changes in impacts and shifting sources have interconnected tradeoffs, making the water-enegy nexus a key part of managing environmental problems such as climate change. Future energy and water supplies are also likely to show higher interdependencies, which may or may not improve regional sustainability. This work offers a way to combine four important sets of information to enable the generation of answers to key regional planning questions around these two key resources