Earth Watch Report - Drought
Plant Stress Paints Early Picture of Drought
by Kathryn Hansen for Goddard Space Flight Center
Greenbelt MD (SPX)
 Plant stress on on August 28, 2012, indicated significant drought in the U.S. Midwest. Credit: NASA/Goddard Scientific Visualization Studio/USDA-ARS |
In July 2012, farmers in the U.S. Midwest and Plains regions watched crops wilt and die after a stretch of unusually low precipitation and high temperatures. Before a lack of rain and record-breaking heat signaled a problem, however, scientists observed another indication of drought in data from NASA and NOAA satellites: plant stress.
Healthy vegetation requires a certain amount of water from the soil every day to stay alive, and when soil moisture falls below adequate levels, plants become stressed. Scientists with the U.S. Department of Agriculture’s Agricultural Research Service (USDA-ARS) have developed a way to use satellite data to map that plant stress. The maps could soon aid in drought forecasts, and prove useful for applications such as crop yield estimates or decisions about crop loss compensation.
“Crop drought monitoring is of high practical value, and any advance notice of drought conditions helps the farmer make practical decisions sooner,” says Steve Running, an ecologist at University of Montana in Missoula.
A new animation of plant stress (top) shows how drought evolved across the United States from January 2010 through September 2012. In spring 2010, satellites measured cool leaf temperatures, indicating healthy plants and wetter-than-average conditions (green), over many areas across the country.
By summer 2011, satellites saw the warming of stressed vegetation, indicating significantly lower-than-usual water availability (red) in many areas, most notably in Texas. Crops were either dead or would soon be dead.
Drought in 2012 was the most severe and extensive in at least 25 years, according to the USDA’s Economic Research Service. By August 60 percent of farms were in areas experiencing drought, and by mid-September USDA had designated more than 2,000 counties as disaster areas.
“2012 was record-breaking, this was just a huge event,” says Martha Anderson with USDA-ARS in Beltsville, Md., who is working with a team to develop the plant stress indicator for drought and presented the research Dec. 5, at the American Geophysical Union meeting in San Francisco.
The 2012 event is what experts call a flash drought, meaning that it evolved quickly and unexpectedly. Low soil moisture was further depleted by the heat wave that started in May, and drought abruptly followed. By about May 5 the core regions of drought began to appear on the plant stress map – earlier than the signs of drought appeared in other indicators, such as rainfall measurements.
“We think there’s some early-warning potential with these plant stress maps, alerting us as the crops start to run out of water,” Anderson says.
Signals of plant stress may often appear first in satellite-derived maps of vegetation temperature before the crops have actually started to wilt and die. “The earlier we can learn things are turning south, presumably the more time we have to prepare for whatever actions might be taken.”
For example, farmers may decide they need to buy supplemental feed from outside the drought-affected area to support their livestock, or they may need to adjust contract or insurance decisions.
The U.S. Drought Monitor already uses a combination of indices, such as rainfall, to describe drought conditions each week. The monitor currently does not include plant stress, but the potential is being explored.
“Plant stress is one representation of drought impacts, and the drought monitoring community agrees that you can’t do this with just one tool – you need a lot of different tools,” Anderson says.
Plant stress information has the potential to improve the skill of existing forecasts that predict drought out to weeks or months. Also, because the plant stress information is derived from satellites, it can describe drought conditions in areas where rain gauge and radar networks are sparse – and it can do so at the scale of individual fields.
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- Plant Stress Paints Early Picture of Drought (seeddaily.com)
- Plant stress paints early picture of drought (phys.org)
- A New Way to Forecast Drought (Just in Time for All Those Climate Change – Induced Droughts) (theatlantic.com)
- Plant stress paints early picture of drought (eurekalert.org)
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