Mapping Plant Stress
December 6, 2012

NASA, NOAA Use Satellite Data To Map Plant Stress Conditions

Brett Smith for — Your Universe Online

[ Watch the Video: The Evaporative Stress Index ]

This past summer, American farmers watched helplessly as billions of dollars worth of crops succumbed to drought conditions.

In an effort to mitigate the adverse effect of future droughts, scientists at NASA and the National Oceanic and Atmospheric Administration (NOAA) are looking to measure and track a potential bellwether of crop conditions: plant stress.

Healthy plants need a certain amount of moisture to survive and if they begin to lose a significant amount of it, they start to show signs of stress.

Plants release internal heat by transpiring water they have extracted from the soil. When water levels are low, plants lessen their water consumption and reduce the rate of ℠sweating´ from leaf surfaces. This condition results in the plants´ leaves heating up and producing an elevated temperature in the plants´ canopy, which can be detected by NOAA's weather satellites.

Based on the data collected by the satellites, scientists from the two agencies were able to create a map of plant stress that could help to show which crops are susceptible to damage from continued lack of precipitation.

"We think there's some early-warning potential with these plant stress maps, alerting us as the crops start to run out of water," said Martha Anderson, with the U.S. Department of Agriculture´s Agricultural Research Service (USDA-ARS). "The earlier we can learn things are turning south, presumably the more time we have to prepare for whatever actions might be taken."

While farmers cannot make it rain, they might be able to buy additional feed for livestock or make financial decisions based on the known levels of plant stress in their region.

Currently, the U.S. Drought Monitor uses several factors, such as rainfall, to describe drought conditions each week, but the monitor does not consider plant stress data, a possibility that is now being explored. Scientists said the inclusion of this data could add to the different tools the agricultural industry uses to combat drought.

“This is not a drought forecast. It's a map of what's going on right now," Anderson said. "Is there more or less water than usual?"

Determining what is ℠usual´ could be a problem. Experts define normal precipitation by calculating and mapping historical plant stress data from 2000 to the present, the time period for which they have satellite information. Unfortunately, climate change could be influencing and redefining what is normal.

"What was normal back in 1920 is not what's normal now, so the more years we have under the belt the better we can define normal," Anderson said. "But this year is so far out of line with respect to previous years, it is unusual regardless of the period of record used as the baseline."

According to U.S.D.A.'s Economic Research Service, the American drought in 2012 was the most severe and extensive in the last 25 years, at least. By August, 60 percent of farms were seeing drought conditions, and by mid-September the U.S.D.A. had designated more than 2,000 counties as disaster areas.

"2012 was record-breaking, this was just a huge event," said Anderson.