The GTAP Land Use Data Base and the GTAPE-AEZ Model: Incorporating Agro-Ecologically Zoned Land Use Data and Land-based Greenhouse Gases Emissions into the GTAP Framework

Abstract

The paper describes the on-going project of the GTAP land use data base. We also present the GTAPE-AEZ model, which illustrates how land use and land-based emissions can be incorporated in the CGE framework for Integrated Assessment (IA) of climate change policies. We follow the FAO fashion of agro-ecological zoning (FAO, 2000; Fischer et al, 2002) to identify lands located in six zones. Lands located in a specific AEZ have similar (or homogenous) soil, landform and climatic characteristics. The six AEZs range over a spectrum of length of growing period (LGP) for which their climate characteristics can support for crop growing. AEZ 1 covers the land of the temperature and moisture regime that is able to support length of growing period (LGP) up to 60 days per annum. On the other end of the LGP spectrum, lands in AEZ 6 can support a LGP from 270 to 360 days per annum. Crop growing, livestock breeding, and timber plantation are dispersed on lands of each AEZ of the six, whichever meets their climatic and edaphic requirements. In GTAPE-AEZ, we assume that land located in a specific AEZ can be moved only between sectors that the land is appropriate for their use. That is, land is mobile between crop, livestock and forestry sectors within, but not across, AEZ’s. In the standard GTAP model, land is assumed to be transformable between uses of crop growing, livestock breeding, or timber plantation, regardless of climatic or soil constraints. The fact is that most crops can only grow on lands that is under certain temperature, moisture, soil type, land form, etc.. The same concern arises for land use by the livestock and the forestry sectors. Lands that are suitable for growing wheat may not be good for rice cultivation alike, even under transformation at a reasonable cost. The introduction of the agro-ecological zoning in GTAP helps to clear up the counterfactual assumption in inter-sectoral land transition, and permit a sound presentation of sectoral competition for land.