Documentation for GCAM
The Global Change Analysis Model
View the Project on GitHub JGCRI/gcam-doc
Table 1: Inputs required by the demand module 1
| Name | Resolution | Unit | Source |
|---|---|---|---|
| Historical demand for agriculture (used for calibration) | By region, demand, commodity, and year | Mt/yr | Exogenous |
| Historical demand for livestock (used for calibration) | By region, demand, commodity, and year | Mt/yr | Exogenous |
| Historical demand for forest (used for calibration) | By region and year | billion km3/yr | Exogenous |
| Commodity prices | By region, commodity, and year | 1975$/kg or 1975$/m3 | Marketplace |
| Income and price elasticity (for non-food, non-feed) | By region, demand, and year | unitless | Exogenous |
| Scale parameter, self-price elasticity, cross-price elasticity, income elasticity, regional bias, price scaling parameters (for food demand) | By region | unitless | Exogenous |
| Logit exponents | By region and sector or subsector | unitless | Exogenous |
| GDP per capita | By region and year | thous 1990$ per person | Economy module |
| Population | By region and year | thousand | Economy module |
Food demand is based on the approach documented in Edmonds et al. (2017).
Shares of feed are determined by a logit sharing approach, which depends on the relative costs of the different feed options. Demand for feed is determined by the scale of livestock demand and these feed shares
Non-food, non-feed demand, including forestry demand, is determined by price, income, and population size.
The equations that determine food, feed, and forest demand are described here.
where \(A\) is a scale parameter, \(x\) is the income divided by price of materials, \(h(x)\) is the income elasticity, and \(w_i\) is the price of the food input divided by the price of materials times some scale factor, and \(e_i\) are price elasticities.
\(x^{h(x)}\) is calculated all together depending on the type of FoodDemandInput. See StaplesFoodDemandInput::calcIncomeTerm and NonStaplesFoodDemandInput::calcIncomeTerm in food_demand_input.cpp.
\(e_{self} = g_{self} - \alpha * f(x)\), \(e_{cross} = g_{cross} - \alpha_{cross} * f(x)\), where \(g_{self}\) is self price elasticity parameter, \(g_{cross}\) is the cross price elasticity, \(\alpha\) is the share of the total budget for the good, and \(f(x)\) is the derivative of the income term. See StaplesFoodDemandInput::getCrossPriceElasticity, NonStaplesFoodDemandInput::getCrossPriceElasticity, StaplesFoodDemandInput::calcIncomeTermDerivative, and NonStaplesFoodDemandInput::calcIncomeTermDerivative in food_demand_input.cpp.
See also food_demand_function.cpp
Per-capita non-food, non-feed demands (D) from time period t-1 to time period t.
\[D_t = D_{t-1} * (\frac{pcGDP_t}{pcGDP_{t-1}})^{\alpha^i_t} * (\frac{P_t}{P_{t-1}})^{\alpha^p_t}\]where \(pcGDP\) is per-capita GDP, \(P\) is the commodity price, \(\alpha^i_t\) is the income elasticity in time \(t\) and \(\alpha^p_t\) is the price elasticity at time t
See calcDemand in minicam_price_elasticity_function.cpp.
To be completed…
To be completed…
Agriculture and forestry demands
[Edmonds et al. (2017)] EDMONDS, J. A., R. LINK, S. T. WALDHOFF, and R. CUI, 2017: A GLOBAL FOOD DEMAND MODEL FOR THE ASSESSMENT OF COMPLEX HUMAN-EARTH SYSTEMS. Clim. Chang. Econ., 08, 1750012, https://doi.org/10.1142/S2010007817500129.