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Looking Into the Future for Agriculture and AKST | 363

Table A.5.6 Overview of major uncertainties in Watersim model

Model Component

Uncertainty

Model Structure

Food module is based on IMPACT (well established). Water module borrows from Podium, IMPACT and Water accounting methodology (all well established)

Parameters

Output: projections on water demand by basin (128) and country (115), water scarcity indices, production coming from irrigated and rainfed areas, crop water use, water productivity and basin efficiency

Driving force

•   population and GDP growth
•   crop demand
•   improvements in water productivity
•   improvements in basin efficiency

Initial condition

Parameters are calibrated to the base year (2000). Based on the best available data sources, uncertainty minimized as far as possible, but in particular water use efficiency data are sketchy in developing countries

Model operation

Runs in GAMS

Table A.5.7 Level of confidence for scenario calculations with Watersim model

Level of Agreement/ Assessment

High

Established but incomplete:
•   Areas suffering from water scarcity
•   Virtual water flows due to food trade

Well-established: Global estimates and projections of crop water use

Low

Speculative:
•   Crop losses due to water shortages
•   Impacts of environmental flow policies on food production

Competing Explanations:
•   Projections of irrigated areas and production
•   Projections of rainfed areas and production
•   Projections of irrigation water demand
•   Projections of water productivity

 

Low

High

 

Amount of Evidence (Theory, Observations, Model Outputs)

•     Sub-Saharan Africa investment study
•     ICID - India Country paper
•     Scenarios at basin level for the benchmark basins in the Challenge Program on Water and Food

A.5.4.4 Uncertainty
The water and food modules are calibrated at the base year 2000 and 1995. Model outcomes aggregated at a relatively high level (globe, continent, major basins such as the Indo-Gangetic) tend to have a better agreement than outcomes at sub-basin level. This reflects the uncertainty associated with global datasets, shown in Table A.5.6.

A.5.5 CAPSiM

A.5.5.1Introduction
China's Agricultural Policy Simulation and Projection Mod­el (CAPSiM) was developed at the Center for Chinese Agri-

 

cultural Policy (CCAP) in the mid-1990s as a response to the need to have a framework for analyzing policies affecting agricultural production, consumption, prices, and trade in China (Huang et al., 1999; Huang and Chen, 1999). Since then CAPSiM has been periodically updated and expanded at CCAP to cover the impacts of policy changes at regional and household levels (Huang and Li, 2003; Huang et al., 2003).

A.5.5.2 Model structure and data
CAPSiM is a partial equilibrium model for 19 crop, live­stock and fishery commodities, including all cereals (four types), sweet potato, potato, soybean, other edible oil crops, cotton, vegetable, fruits, other crops, six livestock products, and one aggregate fishery sector, which together account for more than 90% of China's agricultural output. CAPSiM is simultaneously run at the national, provincial (31) and household (by different income groups) levels. It is the first
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