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Seasonal climate variability and crop yield forecasting

Hafi, Ahmed Mr; ph. (02) 6272 2081; fax (02) 6272 2001; AHafi@abare.gov.au

Research Organisation: Australian Bureau of Agriculture and Resource Economics, GPO Box 1563, Canberra ACT 2601

Collaborator: Agriculture Western Australia (Dr David Stephens)

Sponsor: LWRRDC, Land and Water Resources Research and Development Corporation

Objectives:

1. to make operational the Weighted Rainfall Index (WRI) model of Stephens et al. (1994) for ABARE to make yield forecasts for wheat;

2. to establish if significant relationships exist between the weather induced variability of wheat yields and the weather-induced variability in yields of other major winter grains;

3. to test whether there is any relationship between the SOI and grain yields for the United States, Canada and Argentina;

4. to establish if significant relationships exist between wool fleece weight and rainfall, and between carcass weights and rainfall.

Methodology:

A Weighted Rainfall Index constructed by Stephens et al. (1994) has been found to explain 87-92 per cent of the variability of wheat yield in the eastern States of Australia, and 67 per cent of the variability in Western Australia. Stone and Auliciems (1992) found that growing season rainfall could be accurately grouped into five phases based on the change in the SOI in autumn. In this study, a modified form of the WRI model was used, where yield forecasts for each month were made by using the future monthly rainfall derived from the state of the southern oscillation, based on the relevant SOI phases at the time of forecast, instead of simply assuming the mean monthly rainfall.

The ABARE wool clip forecasting model (Shaw and Findlay 1990) is based on the GROWEST model of pasture production (Flavel et al. 1987). This model generates forecasts of pasture growth indices which are combined with estimates of sheep and lamb numbers and other demographic characteristics to derive forecasts of wool production per head. SOI-base rainfall forecasts, instead of median-based forecasts, were incorporated into the model to see if they led to more accurate prediction of wool clip per head.

Progress:

Yield forecasts using the WRI model were compared against the earlier ABARE system (that assumed mean monthly rainfall) for a number of historical years, and for different points in the growing season. The WRI proved a better predictor of final yields, but for some years the comparison gave inconclusive results. It was concluded that the use of SOI-based rainfall predictions in conjunction with the WRI model had a practical application in commodity forecasting, which ABARE is now using operationally.

As was expected, movements of the correlation coefficients for the United States, Canada and Argentina conform to the opposite effects of the SOI on wheat yields in Argentina. However, even with the highest estimate of the correlation coefficients (~0.50), the SOI alone would be able to explain a maximum of only 25 per cent of the variability in yields of the countries studied.

Generally, in predicting the size of the wool clip, there is little difference between yield forecasts made using median rainfall and SOI-determined rainfall forecasts, in either May or August for all States. Using the wool clip forecasting model in its current form, it is not possible to improve the forecasting accuracy of the model using SOI indications.

Period: starting date 1995-07 ; completion date 1997-04

Status: completed

Keywords: seasonal forecasts, yield forecasts, Southern Oscillation Index

References:

Flavel, N. Collins, D. and Menz, K. (1987). Climatic indices for Australian grazing industries. BAE paper presented at the 31st Annual Conference of the Australian Agricultural Economics Society, Adelaide, 10-12 February.

Shaw, I. And Findlay, C.J. (1990). Forecasting Victorian fleece weights using a climatic pasture index. Agricultural Systems 34, 191-205.

Stephens, D.J., Walker, G.K. and Lyons, T.J. (1994). Forecasting Australian wheat yield with a weighted rainfall index. Agricultural and Forest Meteorology 71, 247-263.

Stone, R. and Auliciems, A. (1992). SOI phase relationships with rainfall in eastern Australia. International Journal of Climatology 12, 625-636.

Publications:

Hafi, A. and Stephens, D. (1995). Wheat yield forecasting. Australian Commodities 2(3), 288-289.

Stephens, D. (1995). Using seasonal climate forecasts for national crop outlook. Proceedings of Managing with Climate Variability Conference 'Of droughts and flooding rains', 16-17 November 1995, Occasional Paper CV03/96, pp. 111-115.

 

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