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GTAP-AEZ

The module uses the following logic. Each nation or sub-region is dis-aggregated to different agro-ecological zones (set aez). If a certain region comprises a certain aez is depicted by the cross-set aezFlag:

In each aez, the total endogenous land use is dis-aggregated to the following three land categories:

The different activities in the model are mapped to these to land categories:

The code does not require that the SAM comprises the full detail of activities, but checks the mapping:

Model equations

The model equations are defined in “gams\GtapAEZ\gatpAez_model.gms”.

The land demand xftAez for each activity in each Aez aez is defined in the equation pftAezEq:

It uses hence a CES approach, where the relation between the average returns for land in the activity defined by the macro m_pfa and the returns in the AEZ drives the allocation of the activity in space. The returns to land use of an activity in the AEZ reflect the specific price net of taxes pftAez plus the nation wide taxes for land use in that activity.

The average return m_pfa uses the usual dual price aggregator defined in the pfaAezEQ:

The average return to land in the AEZ pftTop is a CET aggregation over the prices pftLandCat for the different land categories landCat based on the transformation elasticity omegaAezTop:

The distribution of the total land in the AEZ xftTop to these land categories uses the standard CET equation based on the share parameter gfTop, the price relation and the transformation elasticity, as depicted by the equation xftLandCatEq:

The average land price for each land category pftLandCat is defined in the equation pftLandCatEq using a dual price aggregator and the transformation elasticity omegaAez:

Accordingly, the distribution of the land in each land category to the different activities in the equation xftAezEq is based on the share parameter gfAez, the given total xftLandCat, the price relation and the transformation elasticity:

As land is not mobile across the AEZ, total factor use of land xft and the related price pft are defined by the following tree equations. The first equations sums the total endogenous land sue in each aez xftTop to xft. The second equation sums up total factor remuneration and the third one defines the average price:

Parameterization

The necessary data for the AEZ module must be loaded during the data preparation step. The aezFlags are set depending on finding any land use activities in the aez data base:

The land use by activity is initialized reflecting the global scaling factor as long as it is above a minimum threshold:

If a land use activity is zero in all aezs with data for a region, total land use share are used:

Afterwards, scaling ensures that adding up over the aez recovers the given total:

The prices are initialized to zero, and the aggregates defined from summing up, i.e.: