different commodities in different states. Three examples of state contingent
productions systems included within the model are:
• Vegetables: In the Normal state, the vegetable production activity is
represented by an average return from a range of alternative irrigated
vegetable crops. In the Drought state, water resources are conserved by
planting only a dryland rockmelon crop. In the Wet state, all resources
are transferred to producing tomatoes for the fresh market.
• Sheep/Wheat: This production activity represents a state-contingent
production plan where producers allocate resources between sheep and
wheat production in response to climatic conditions and market forces.
The production mix between the two outputs is 50 per cent wheat, 50 per
cent sheep in the Normal state, 90 per cent sheep and 10 per cent wheat
in the Drought state and 30 per cent sheep and 70 per cent wheat in the
wet state. Effort is placed in keeping the breeding stock alive during the
Drought state while in Wet states there is plenty of fodder available on
the non-irrigated pasture, and irrigated land can be allocated to wheat
production.
• Wet Cotton. The producer irrigates their cotton crop only in the 'Wet'
state of nature. This activity is an example of opportunity cropping.
Representing climate change
The scenarios for climate change imply a reduction in mean inflows. This could
be represented by an equiproportional reduction in inflows for each of the three
states. However this would imply a similar, equiproportional reduction in
variance. Although the catchment-level climate projections used here do not
include projections of variance, the results for global climate change suggest that
the variance of rainfall is likely to increase even where mean values decrease.
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