Forests are workaholics. They do a lot for us. They sequester carbon, mitigating climate change, buffer the flow of nasty pollutants into our waterways, prevent flooding by retaining snowpack and so much more.

If forests were people, you might expect this round-the-clock do-gooding to stress them out. But, plant stress is caused not by busy schedules, but by environmental conditions that don’t support good plant health. Plant stressors include extreme temperatures, pollution, drought and many other factors.

The drought of 2012 was one of the Midwest’s worst.
The drought of 2012 was one of the Midwest’s worst. Credit: Theresa Wysocki/Flickr

It so happens that even under stress, plants — in the forest and in the field — continue to help us out. Plant stress was hinting at the approaching drought of last summer — a drought that turned out to be one of America’s worst — a month before the U.S. drought monitor warned us of it.

In a method revealed last Wednesday at the American Geophysical Union meeting in San Francisco, scientists monitored plant stress using plant surface temperature data captured by NASA and NOAA satellites. Hotter temperatures of the plants’ surfaces indicated that they were not finding enough water in the soil to “sweat” and cool themselves off.

The video below shows this data — called the Evaporative Stress Index (ESI) — for 2010 through 2012. Red areas indicating low soil moisture as early as May 2012 are the first signs of the drought of that summer.

Seeing a drought coming doesn’t mean you can stop it, but it does mean you can better prepare for its consequences. The extra month of warning time that this method could provide would allow farmers to prepare for dry years, by stocking up on alternative sources of livestock feed, for example. It could allow municipalities to put stops on lawn watering or set other water usage limits in time to fend off some of the worst effects of a drought.

Ultimately, though, if too many of our forests and other ecosystems become too stressed, an early warning sign could be more like a bad diagnosis. Without healthy vegetation to perform vital ecosystem functions, busy schedules will be the least of our stressors.