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| Projection procedure | ||
| The projections of wine grape production contained in this report are generated from estimates of yields and wine grape bearing areas. Projections are made for up to 47 different varieties of wine grapes in each of the 86 wine regions in Australia. These wine regions are defined by the Australian Bureau of Statistics (ABS), which collects detailed statistics on the Australian grape growing industry each year from grape growers (ABS 2008). The annual ABS wine grape census collection provides information about the current state of Australian viticulture integral to the projections of future wine grape production reported here. As part of the wine grape census, the ABS collects data for each grape variety on the grape bearing area, non-bearing area and the quantity harvested for specific purposes such as wine making and drying. Information is also obtained about the amount of the non-bearing area which was planted or grafted on in the previous 12 months, as well as the non-bearing area which was non bearing for more than a year. Because grapes are perennial, the bearing area of grapes next year is determined mostly by the area of grape vines that are currently bearing fruit. It is also affected by the area of grapes planted or grafted on in previous years which will bear fruit next year (a portion of the current non-bearing area). In addition, it is possible that growers might take grape vines permanently out of production between the current and next year’s harvest; a practice known as grubbing. Based on this intertemporal relationship, the following model is used to estimate future production:  Where Giprojt+1 is projected production of grape variety i, next year; BAi,t is the current bearing area; PLiprojt-k is the portion of the current non-bearing area which was planted or grafted on in an earlier year t–k, but is projected to be bearing next harvest (k = 3 for warm climate regions and k = 4 for cool climate regions); RMiprojt+1 is the projected area of vines of grape variety i which will be removed or grubbed next year, and Yiprojt+1 is the estimate of next year’s yield per hectare for wine grape variety i. The portion of the current non-bearing area expected to come into bearing in the future is determined by estimating an age profile of the current non-bearing area which is more than one year old — that is, the area that was not planted (or grafted on) last year. The age profile of the non-bearing area two years of age and older is assumed to reflect the relative size of new plantings (and grafting on) over recent years. For the cool climate regions it is assumed that it takes four years for newly planted vines to reach a commercial bearing age, while in the warm inland regions it is assumed to take three years. For example, for warm climate regions, the proportion of each variety planted two, three and four years ago of total plantings over that period is used to apportion the total non-bearing area that is currently reported to be at least two years old. The apportioned areas provide estimates of PLiprojt-k, the areas that are to become bearing in the future. For cool climates the plantings of each variety two, three, four and five years previously would be used in a similar manner to the warm climate regions to determine the additions to bearing area in the future. Ideally, the area grubbed next year should be subtracted from the bearing area. However, given the small area of grapes which have historically been grubbed or grafted off according to ABS data, and given future decisions by growers to grub are too difficult to estimate with any objectivity, they were assumed to be zero and excluded from the projections model. According to the model provided above, estimated wine grape production for each variety in 2008-09 is calculated as the sum of the 2007-08 bearing area and the portion of non-bearing area reported in 2007-08 expected to reach commercial bearing in 2008-09 (four years old in cool climate and three years old in warm climate regions), multiplied by the projected yield in 2008-09. To forecast grape production for the following year (2009-10), the area expected to become bearing in 2009-10 is added to the estimate of the bearing area in 2008-09 and the total area multiplied by the projected yield. |
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| Calibration | ||
| Previously, estimates of wine grape bearing areas collected by the ABS have been calibrated using production estimates collected by the Australian Regional Winegrape Crush Survey (ARWCS). This was done because the ARWCS historically had greater coverage of wine grape growers and accordingly the production estimates from this survey were greater than those estimated by the ABS survey. In recent years, the coverage of the ABS vineyards survey has improved and the ABS estimate of wine grape production in 2007-08 was 4 per cent higher than the ARWCS estimate. Because of this, ABS production estimates have not been calibrated to the ARWCS results when compiling the projections contained in this report. In most cases, this has little impact. However in some regions, the projections contained in this report should not be compared with previous publications. Multipurpose and some minor grape varieties are commonly used for purposes other than for making wine. Therefore, production projections for these types of grapes based only on the bearing area of these vines would typically far exceed their use for wine. Accordingly, production estimates of multipurpose and minor variety grapes in these projections have been calibrated using the proportion of these grapes used for making wine in 2007-08. |
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| Yields | ||
| Industry experts provided the yields which were used to project production. Historical yield data for each variety of grape for the previous five harvests and the average yield for that five year period were provided as base information to the industry experts for each region. These experts then provided their own estimates of yield for the 2008-09 harvest and each of the projection years. It was not uncommon for industry experts to expect the yields at the end of the projection period to be similar to the five year average yield. | ||
| Aggregation of regional projections | ||
| For reporting purposes, the projections of wine grape production are presented at the Australian, and the GI zone and region level. The vast majority of regions defined by the ABS in the wine grape census are identical to the GI regions but in some cases the ABS collects data at a more disaggregated sub-regional level particularly where GI regions or zones cross state borders. In these instances, ABS regional projections were aggregated to the GI region (zone) level. In some instances, such as for the Murray-Darling–Swan Hill GI, the GI zone is also the region. As a result, the 90 ABS regions used in the projections model become aggregated into 86 GI regions. The tables for wine grape production in each of the 28 GI zones presented in appendix B are simply aggregations of the projections generated at the GI region level. Projections of wine grape production, by variety, for each of the 86 GI regions can be accessed from ABARE’s website. |
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