South African farmers were consistently underestimating their output in order to keep prices artificially high

Satellite imagery improves South Africa's crop forecasts

South Africa's estimates for key crops such as maize have become increasingly accurate thanks to satellite imagery.

The technology also eliminates bias from farmers, which used to result in many underestimated crop size forecasts due to incorrect input data.

From 1997 to 2002, all of the maize forecasts made by the official Crop Estimates Committee (CEC) underestimated the size of the harvest, said Eugene du Preez, director of privately-held SiQ, which provides the committee with satellite and aerial data, which helps it determine the size of the area planted.

South Africa's maize crop has been hit hard this season by a scorching drought, bringing into sharp focus the need for accurate forecasts of the harvest's size to guide government policy and markets.

"That was a red flag," Du Preez said. The reasons for the underestimates were clear, as the CEC was relying on farmers for much of its information and they had a transparent incentive to say they had planted less than they had because that would support prices.

Du Preez said from 2003 until 2008, five of the six forecasts underrated the size of the crop.

"We started providing the government with data in 2002, and at that stage we were still very much providing them with information coming from farmers, and there was problems with that," he said.

"And then we decided we needed to change the system. So we developed the producer independent crop estimate system."

The system uses both satellite images and aerial surveys conducted with the use of low-flying aircraft to create a complete picture of crop production.

For yield estimates, the CEC heavily relies on on-site surveys conducted by the state-run ARC Grain Crops Institute.

"They are doing work in the three main maize provinces, Mpumalanga, Free State and North West," said Marda Scheepers, a senior statistician with the CEC.

"They go into a field and they do crop counts and plant counts to get an average yield for the province," she said.

From 2009 to 2015, crop estimates were more representative of the actual output as a result of the satellite system.

The CEC said it had three underestimates and four overestimates in that time and these have been closer to the actual crop size than previous figures.

Forecasts were routinely six or seven per cent off target from 1997 to 2002, at worst being close to 13 percent out.Yet Du Preez said the average since 2009 has dropped to just 2.6 per cent and last year the difference between the CEC's final forecast and the size of the harvest was 0.2 per cent.

South Africa will likely harvest 7.1 million tonnes of maize in 2016, 29 per cent less than the 9.95 million tonnes reaped last year because of drought and late plantings.

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