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.