The Water Footprint of Fuel Ethanol
Alvarez, Pedro J.
Doctor of Philosophy
Biofuels (Le., biomass-derived fuels) play a key role in discussions in the United States about energy security, agriculture, taxes and the environment. Although their potential to reduce our dependence on foreign oil and to mitigate climate change is still being debated, biofuels constitute a renewable domestic resource, offer advantages to air quality improvement, and provide alternative revenue for agricultural producers. In 2007, Congress enacted the Energy Independence and Security Act (EISA), which mandates the production of 36 billion gallons per year (BGY) of biofuels by 2022, including 15 BGY of corn-derived ethanol. This large increase in demand for biofuels requires immediate consideration and mitigation of unintended environmental impacts. Specifically, there is concern that the potentially high water demand for biofuel production could result in added pressure to already scarce water resources across the country and become, in many cases, the main limiting factor to biofuel production. The extent of the impact created by different crops and across agricultural regions is unknown but could potentially be large. In addition, climate change could ameliorate or worsen the water footprint of biofuels through several mechanisms. First, it could either reduce or increase rainfall and water availability. Secondly, water use by crops will change as a result of the combination of several factors influenced by climate change (notably temperature, precipitation and C02 concentration in the air), which interact in complex ways. Finally, climate changes will be markedly regional and biofuels production is also highly concentrated in one particular region of the United States, potentially magnifying the effects on water resources of large scale production. To answer these important questions, we calculated the water requirements for biofuel production from mUltiple cash crops (i.e., corn, soybean, switchgrass, sorghum, potatoes, and sugarbeet), taking into consideration the region they are currently grown. This is done through a life cycle analysis (LCA) methodology and based on existing US Department of Agriculture (USDA) and industry statistics. We also estimated the effects of climate change in the water demand of corn, the most prominent biofuel crop, using a large-scale distributed agricultural model and projections of climate change from coupled General Circulation Models (GCMs). Climate projections from five different models were used to include a wide range of future climate scenarios. This approach is necessary given the large differences in projected precipitation that exist between different climate models. The magnitude of projected increase in water requirements varied across the five simulations but the trend was consistently upwards in all of them. Overall, this thesis will enhance decision making by contributing with a tool that can provide spatially distributed projections of water requirements for biofuel crop agriculture. The location of future biofuel crop acreage is unknown at this time, which precludes accurate discernment of where and to what extent water shortages are likely to occur. Nevertheless, model simulations underscore the importance to consider irrigation requirements and water resources availability prior to selecting biofuel crops and where to grow them to avoiding straining regional water resources and jeopardizing future biofuel production. Specifically, our analyses show that the consumptive water demands associated with biofuel crop agriculture ranges from 500 to 4,000 liters of water for liter of fuel ethanol produced under current climatic conditions. Simulations with corn showed that by mid century corn crops in traditionally irrigated areas of the High Plains might require significantly more water (up to 40% in some areas) and that biofuels production now taking place in traditionally rainfed areas of the Midwest might require irrigated water supplies, potentially placing a major strain on water resources in that region, if not analyzed and managed properly. This analysis suggests that u.S. biofuels policy will have to be adjusted in the coming years to avoid exacerbating the substantial pressures that climate change are expected to have on certain regions of the United States and on national food production. In particular, the Ogallala Aquifer, the main source of irrigation water in the High Plains, is already experiencing significant water table drops and could be significantly threatened by a continuation of current biofuels policy in the context of projected climate change outcomes.
Civil engineering; Environmental engineering