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The world is losing soil at a dangerous rate. Wind, rain, land-use change and deforestation can all cause soil to erode and see the rich, fertile topsoil removed. In turn, this can lead to failed harvests, water pollution and an ever-increasing requirement for chemical fertilisers. Last August’s IPCC report on climate change and land use highlighted soil erosion as a significant risk to global food security.
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But when it comes to soil, not all countries are equal. Using satellite imagery, researchers from ETH Zurich and the University of Basel have created a world map of soil erosion, demonstrating where rates are highest and lowest. Crucially, the map reveals significant differences at country borders, suggesting that it’s not just geography and climate which affect erosion, but also a country’s socio-economic policies.
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Aerial image showing the difference in greenery between China and Kazakhstan [Image: NASA]
The most extreme example is the island of Hispaniola – the Caribbean landmass home to the Dominican Republic and Haiti. The researchers found that along the border, Haiti’s soils lose 50 tonnes more per year and per hectare than those of the Dominican Republic. By comparison, the rate of erosion in Germany is 0.2 tonnes lower than that of its neighbouring countries.
‘These unnatural jumps are extremely common,’ says David Wuepper, lead author of the study. ‘If you just look at cropland, you see that in the United States, the land is completely full of vegetation because they use fertiliser and irrigation. In Mexico, it’s much more bare, so the soil is more sensitive to erosion in Mexico compared to the US. There’s a similar thing at the border of China and Kazakhstan. China is completely green and Kazakhstan is completely brown.’
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The US is covered in farmland (coloured in red), while land in Mexico is only punctuated with fields [Image: NASA]
The reason for these differences vary, but often it comes down to the type of crop grown. Wuepper points to any crop that results in bare patches of land as potentially damaging for soil. Sparsely planted olive groves or fields of corn which remain barren for a portion of the year are known to be soil eroders.
Nevertheless, Wuepper sees these results in a largely positive light. ‘What I found most interesting about this research is that it suggests there is large potential for countries to do something about soil erosion,’ he says. ‘Before, all the literature talked about soil erosion as a very local problem, which it can be. But farmers can do a lot to avoid it. For example, you can plant cover crops and protect the soil by planting something else. But it is quite country specific, so it’s mostly up to the country to set the right incentives and the right regulatory system.’
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