Background: Recent studies have evaluated the land use consequences of biofuel programs and the associated carbon fluxes. However, all of these studies have effectively ignored the distinction between rainfed and irrigated lands and neglected the facts that irrigated croplands typically have much higher yields than their rainfed counterparts in the same region and that expansion in irrigated crops are limited in some regions due to water scarcity and irrigation constraint. This paper shows that these omissions introduce systematic biases in the measurement of biofuel-induced land use change emissions.
Methods: A new computable general equilibrium model which distinguishes irrigated and rainfed agriculture is developed. The new model is an enhanced version of the publicly available Global Trade Analysis Project model with Biofuels (GTAP-BIO) which has been widely used in this field frequently. To distinguish irrigated and rainfed agriculture, the biophysical component of the GTAP-BIO model is extensively modified using the most recent published data in this area. The economic component of the model is also modified to handle the distinction between irrigated and rainfed agriculture.
Results: We find that ignoring the irrigated-rainfed distinction modestly underestimates global land use change, but results in sharply different geographic patterns of cropland expansion, with stronger rainfed expansion in more carbon-rich environments. This points to a significant underestimate of land use emissions in earlier studies.
Conclusions: To provide more accurate estimates of biofuel-induced land use emissions, it is critical to incorporate the role of irrigation in crop production, taking into account the fact that expansion in irrigation is constrained in some regions across the world.
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