A month before rainfall measurements or other drought indicators picked it up, satellite data showed what was coming for the American South and Midwest: hot, water-stressed crops that eventually died under a prolonged drought.
Scientists at the U.S. Department of Agriculture have developed a way to harvest numbers from NASA and National Oceanographic and Atmospheric Administration satellites and turn them into a map of plant stress. Now, they say, their maps could help the U.S. predict and prepare for drought sooner.
"We think there's some early-warning potential with these plant stress maps, alerting us as the crops start to run out of water," Martha Anderson, a physicist with the USDA's Agricultural Research Service, said in a statement. "The earlier we can learn things are turning south, presumably the more time we have to prepare for whatever actions might be taken."
Earlier predictions may have reduced the fallout from this year's drought, which was a "flash drought" that started unexpectedly. More than 60 percent of the U.S. eventually was stricken by the drought, which the USDA expects to drive up the prices of meat, dairy and eggs in 2013.
Had farmers known about the drought earlier, they could have bought extra feed for their animals or adjusted any contracts they signed, according to a NASA statement.
Farmers may also lean more on predictions as scientists expect droughts to occur more frequently in the future because of global warming.
Satellite maps have another advantage. They could expand coverage in areas where there are fewer water gauges, NASA said. Satellites are able to record the conditions of individual fields anywhere in the U.S.
NASA's Terra and Aqua satellites measure the temperature of the earth's surface, and are able to distinguish the parts of the earth covered with plants. The temperatures of plant-covered areas tell scientists how well watered the plants are, because an abundance of water in the soil allows plants to keep cool by letting excess water evaporate out of their leaves.
When plants sense their soil is dry, however, they shut the pores in their leaves to try to save water and, as a result, their leaves get hotter.
Anderson's team compares its plant-temperature maps with data from previous years, to determine if fields are drier than what's normal for that time of year. Drier fields may mean a coming drought.
The new plant stress data would join rainfall and other measures that describe and predict droughts. Using a variety of data and prediction tools is best, Anderson said.
Anderson and her team presented their work Dec. 5 at a conference hosted by the American Geophysical Union.