Farmers around the world are growing more crops than previously thought, according to a new high-resolution satellite map.
Researchers at the United States Geological Survey (USGS) have pieced together a map using Landsat satellite imagery with 30-metre resolution that identifies every plot of land under cultivation around the globe.
The map shows that 4.62 billion acres are being farmed, which is 15 to 20 percent higher than previous estimates.
That finding did not surprise Prasad Thenkabail, USGS research geographer and principal investigator of the Global Food Security Support Analysis Data project.
He knew the higher resolution satellites would pick up on areas never before mapped or were inaccurately identified as non-croplands.
For instance, the Landsat satellites can find farmland located along the margins of forests and deserts that previously went unnoticed.
“The map clearly shows individual farm fields, big or small, at any location in the world,” said Thenkabail.
The map can be used to improve insights into global food security and water use.
When the Food and Agriculture Organization (FAO) of the United Nations produced its oft-cited 2009 study calling for 70 percent more food production by 2050, it used a baseline of 3.95 billion acres of farmland.
The FAO said land under cultivation would have to expand to 4.12 billion acres by 2050. The USGS map shows the world is already well above that number.
Thenkabail doesn’t know how the FAO arrived at its 70 percent number, but he suspects it would change given the new global acreage estimate.
“If you get your base line area wrong, then productivity is naturally going to be wrong,” he said.
“It’s very important to get this one right.”
The new map shows India possesses the highest net cropland area, accounting for 444 million acres or 9.6 percent of total global farmland. Earlier studies showed that either China or the United States were tops.
The U.S. is second with 8.9 percent followed by China at 8.8 percent and Russia at 8.3 percent. Canada accounts for 106 million acres or 2.3 percent of global cropland.
Cropland makes up more than 80 percent of some countries such as Moldova, San Marino and Hungary. In Canada, it accounts for five percent of total land mass.
Thenkabail said it was painstakingly difficult to create the map. Researchers used composite data from 2013 to 2015.
“One major challenge was obtaining cloud-free images in regions such as the tropics and during rainy seasons. That took multiple years in some areas,” he said.
The map was created using machine learning algorithms on the Google Earth engine. It was validated by an independent team for 72 zones across the world.
“I call it kind of the mother of all big data,” said Thenkabail.
The map can be updated annually or each season.
“This map is a base line and starting point for higher level assessments, such as identifying which crops are present and where and when they grow, their productivity, if lands are left fallow and whether the water source is irrigated or rain fed,” he said.
“Comparisons can be made between the present and past years, as well as between one farm and another.”
The map is free and can be found at croplands.org.