Frank Eckardt was setting up his equipment on a peanut field in August 2018 when he got hit by a dust storm. For the excited geomorphologist, it was over too soon.
“We were in the right place at the right time,” says the associate professor at the University of Cape Town’s environmental and geographical science department, of that morning near Bultfontein in the Free State.
“We have been looking at these things in satellite images and hearing about them from farmers, but there’s nothing like witnessing them because they’re not too frequent.”
Eckardt is the co-author of a new report that shows how windborne dust from large tracts of Free State croplands, devastated by the 2015-2016 drought, are a cause of South Africa’s dust — and a “red flag” for food security. Most of the country relies on the Free State maize fields for staple foods.
The research aimed to identify the country’s dust sources using Spinning Enhanced Visible and Infra-red Imager data between 2006 to 2016. “The western Free State is clearly the most emissive dust producing area in South Africa,” he says.
The paper, published in the journal Aeolian Research, says that in Botswana and Namibia dust originates mostly from dry rivers and lakes, but South Africa’s case is unusual because most of its dust is from exposed agricultural lands, particularly during a drought.
A total of 334 497 satellite images identified 178 dust plumes originating from the Free State over 75 dust days between June to January 2006 to 2016.
These months are the region’s dust emission season. These storms overlap with the dry season and coincides with the maize harvest period.
“2015 and 2016 saw almost half of all event days in the 11-year record, which was matched by a severe drought index and stronger winds,” says Eckardt. “These were really very unusual conditions.
“What’s interesting is to go to these farms in August after harvest when the farmers have managed to get their yield and bring home their maize. But if you go there in November and December, [the farmers are] on edge. If that rain doesn’t come in the right amount at the right time, the crops fail. The stakes are huge.”
Eckardt says that understanding dust emission dynamics from farming in drylands is vital. If the soil is blown away it means fine materials such as microorganisms, carbon, nutrients and the ability to hang on to water disappears as well.
Efforts by farmers to try to keep some stubble or cover crop on denuded farmlands “are patchy” and the Free State’s large dairy herds trampling and grazing in a degraded field can cause more damage.
Government crop data reported a decline in Free State maize cover from 1.2-million hectares to 0.6-million ha and an increase in fallow land from 140 000ha to 790 000ha over the same period.
Free State farmer Pierre van Eeden says the wind is usually hot, with very little moisture, making the effects far worse.
“These dust storms were also present 20 to 30 years ago, but were coupled with thunder showers very soon after.”
Strong winds with a lot of dust or sand particles can damage plants, especially younger plants.
“Farmers lose topsoil through wind erosion that can never be replaced, which also affects yield through the sandblasting,” says Van Eeden. “In the long run this has an adverse effect, lowering crop production and red meat production, causing supply and demand to take effect and increasing the price of food for South Africans.”
Fifteen years ago the planting season started in October, after the winds of August and September and sufficient rain has fallen. His planting window for summer crops has moved forward by a month to six weeks. “This causes the plants, especially maize, to physiologically die off before being fully matured. We’ve seen this in the two previous seasons, affecting the grade of maize harvested not fit for human consumption,” Van Eeden says.
Eckardt’s paper also refers to dust storms that happened more than a century ago.
“Some of these things are natural, some are enhanced by human activity,” he says. “Telling one apart from the other is not straightforward. The response farmers can bring to the table during a drought can make a huge difference.”