Is there an Existing Model of Computing Rice Sufficiency?
Rice production and yield, like any other agricultural crop depends on a number of factors. These include, but not limited to:


The variety of rice being grown
The fertility of the soil, and this can and does vary between regions
in countries
The availability of water for the variety of rice
Loss due to pests or natural events (ie weather)


When new varieties of rice are developed, test plots are planted in various locations and the yield per area of land, typical tonnes per hectare, are ascertained. Once this has been done for a number of test plots and for a number of growing seasons, average numbers of tonnes per hectare can then be applied to larger/national plantings.

Combine this with data regarding the number of people that need to be fed and the determined average of the amount of rice each person needs it is possible to determine the sufficiency of a rice production.