Water use impacts of future transport fuels: The role of California's climate policy and national biofuel policies

Introduction

In the coming decades, growing demand for energy and water and the need to address climate change will create huge challenges for energy policy and natural resource management. Synergistic strategies must be developed to conserve and use both resources more efficiently. California (CA) is a prime example of a region where policy has began to incorporate policies to use scarce water resources wisely in energy infrastructure development, even while adopting GHG mitigation targets.

Methodology

We analyze life cycle (LCA) water use of CA's current and future transport fuel consumption to evaluate impacts and formulate mitigation strategies for at the watershed scale. Four “bounding cases” for CA's future transportation demand are projected to year 2030: two scenarios that only meet the 2020 climate target (business-as-usual, BAU) with high/low water use intensity (WUI), and two that meet long-term climate targets with high/low WUI. We assess the main transport energy supply chains: (a) liquids from conventional/unconventional oil and gas, (b) thermoelectric and renewable generation technologies, and (c) biofuels.

For biofuels we extend our scope to the entire USA as most of the biofuels consumed in California are and will be produced from outside of the state. We analyze policy impacts that capture both direct and indirect land use effects across scenarios, thus addressing the major shortcomings of existing studies, which ignore spatial heterogeneity, as well as the economic effects of crop displacement and the effects of crop intensification and extensification. We use the agronomic-hydrologic model EPIC to capture both green water (GW) and blue water (BW) use at a 10 km resolution among three scenarios: (1) a counterfactual with no national biofuel policy, (2) current Renewable Fuels Standard (RFS) mandates, and (3) a proposed national Low Carbon Fuel Standard (LCFS) plus the RFS scenario. Inputs are spatially explicit: (a) cropping areas and yields, projected by a partial equilibrium economic model, (b) daily weather data, (c) soil properties (d) N fertilizer application, and (e) irrigation sources and volumes, by crop.

We assess the differences among biofuel scenarios from 2007-2035 along the following metrics: (1) crop area expansion on prime and marginal lands, (2) Crop-specific and overall annual/seasonal water balances including (2a) water inflows (irrigation and precipitation), (2b) crop-atmosphere interactions: (evaporation and transpiration) and (2c) soil-water flows (runoff & soil infiltration), in mm³ /acre.

Results

We develop plausible siting scenarios that bound possible water sources, impacts, and dispositions to provide insights on infrastructure siting and limit water impacts of supplying energy. We identify opportunities to improve water use efficiency and highlight salient policy relevant lessons.

Conclusions

We find differential water use impacts among biofuel scenarios are a primarily a function of (1) land use conversion, in particular use of formerly uncropped land, (2) irrigation, (3) feedstock water use efficiency, and (4) the longer growing season and predominance of rainfed cultivation of dedicated biofuel feedstocks.

Please note these Proceedings have received limited or no review from supervisors and IIASA program directors, and the views and results expressed therein do not necessarily represent IIASA, its National Member Organizations, or other organizations supporting the work.

Last edited: 19 August 2015