Information Technology Reference
In-Depth Information
3
Model Description
This section first describes the general model setup and some aspects of farmers'
decision-making which are identical for both models, which are presented afterwards.
For a more detailed description see [10] or the model description provided at
www.openabm.org.
3.1
General Setup
Each agent represents a farm. Agents are classified in three different types (part-time
farms, family farms and business farms) and five different farm size classes (very
small: 46,5% of all farms, 4 ha, mostly part-time farms; small: 35%, 8 ha, mostly
family farms; medium1: 12%, 32 ha, mostly family farms; medium2: 4,7%, 70 ha,
mostly business farms; big: 1,8%, 150 ha, mostly business farms).
One step in the model represents one year in reality. The simulation covers a
period from 1960 to 2009. Each step farmers have to decide on their land-use pattern.
A land-use pattern is defined as a combination of different land-uses. A crop
combined with an irrigation technology is an option, whereas one option together with
its related area forms a land-use. Land-uses are not located spatially, but land-use
patterns are stored as lists of pairs {option, area} related to farmers. In total the model
contains nine different crops: traditional cereals (wheat, barley), sunflower, high yield
cereals (maize, alfalfa), sugar beet, vineyards, olives, melon, paprika and garlic, and
four different irrigation technologies (flood-, sprinkler-, drip-irrigation or rainfed).
Overall there is an amount of 23 options
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. Prices, variable costs (rainfed/irrigated),
yields (rainfed/irrigated),
water needs for irrigation, risk and labour input needed
(including scale effects) for crops, as well as efficiency of irrigation technologies are
given exogenously and based on empirical data. Different regulations are
implemented, which imply subsidies or penalties for specific crops and amounts of
water use: EU- Common Agricultural Policy influencing crop prices (CAP, 1993
onwards), Spanish Water Act introducing pumping quotas (1985 onwards), Spanish
Vine irrigation banishment (up to 1996), EU Agro Environmental Programme
providing subsidies for limited water use (AEP, 1993 onwards, substantially modified
in 2003).
3.2
Identical Model Elements
All farmers are assumed to have the same set of objectives, although those may be
weighted differently by different farmer types. Those objectives are having a high
gross margin, having low risk, having low labour loads and staying legal. These
objectives are derived in [10] based on the general literature on farmer behavior and
case-specific information and can be briefly justified as follows: profit and risk
aversion are standard considerations when modeling western farmers. Further, in the
Guadiana, many farmers take more groundwater than granted. Expecting that all
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Not all combinations of crop and irrigation technology are feasible.
