Improving direct land use change calculations: an Australian case study

Abstract

Direct land use change (dLUC) can contribute significantly to carbon footprint and life cycle assessment results. A tool that covers all crops grown in all countries is important to provide high-quality and consistent inventory data but comes with significant challenges managing data. This analysis shows that the use of such high-level data in a commonly used tool to assess dLUC emissions, developed by Blonk Consultants, results in inappropriate dLUC emission factors for Australian production. The review process involved assessing each parameter used in the tool to ascertain whether local Australian data could be implemented. Four parameters were identified, covering soil and climate type, carbon stock in living forest and variation in crop land use. The tool was modified using updated parameters to evaluate the variation in results. The carbon stock in living forest was found to be considerably overestimated. To determine climatic region and soil type, the tool uses the whole area of Australia, while in practice, agricultural production occurs in only a certain proportion of the country with a significantly different climate and soil profile. This second adjustment modifies the reference values for soil organic carbon. Another significant factor was found to be the approach used to calculate cropland expansion. Australian cropping systems include a significant fraction of temporary pasture in rotation schedules with crops and temporary fallow land, which means that cropland encompasses more than the sum of areas harvested for individual crops. On the other hand, summing the area harvested of all crops may result in double counting of land used for cropping where there is more than one crop a year. Finally, using a 3-year rolling average to estimate land use creates a high level of uncertainty for a country where decadal rainfall patterns determine the way land is used in any 3-year period. Greenhouse gas emissions associated with dLUC were estimated to be 82% lower than the result from the tool, when local country-specific data were used. The identified issues could be relevant for other countries. The approach to estimating dLUC could be improved by using local data for carbon stock in forests; the use of aggregated land use categories to estimate expansion and contraction of cropping area over time; and the use of a longer period for estimating the averages on which trends in dLUC are based, so that the impact of drought years is evened out.