The Evaporative Stress Index is a system being developed by the United States Department of Agriculture that uses satellite data to predict drought. An experimental version of the index is online now, and researchers expect the full version will be available next year.
Jason Otkin, an assistant scientist in the University of Wisconsin’s Cooperative Institute for Meteorological Satellite Studies, said the system uses data that show how much moisture plants give off into the atmosphere to predict dry conditions.
As plants draw water from the soil, they release water vapor into the atmosphere through small pores on the underside of leaves, a process called transpiration. Otkin, a member of the team developing the system, said when water becomes scarce and plants are stressed, they give off less water vapor. That change takes place before plants show visible signs of stress like wilting or changing color, he said.
By tracking the amount of moisture plants give off, the system can give farmers and ranchers an idea about when drought conditions are about to appear or intensify, Otkin said. The system can show drought predictions within a window of about 2 to 3 miles, he said.
The tool will be particularly useful for cattle ranchers, Otkin said. For obvious reasons, cattle are more mobile than wheat crops, so when drought is on the way, ranchers have more options for preparing for it.
“Once the wheat’s in the ground, it’s in the ground. There’s not much you can do about it,” he said. “But for ranchers, there is something you can do about it.”
Fighting flash drought
Much of Oklahoma has been in the grip of a persistent drought since 2010. Although a relatively cool, rainy summer has helped the situation, conditions remain dire in parts of western Oklahoma. According to a U.S. Drought Monitor report released Thursday, about 16.6 percent of the state is still in extreme or exceptional drought, the report’s two most severe categories.
Mark Shafer, director of climate services for the Oklahoma State Climatological Survey, said the index will be particularly useful in Oklahoma because it is a good predictor of flash drought. Flash drought occurs when abnormally hot, dry weather cause drought conditions to appear and escalate quickly. Oklahoma’s hot, dry summers coupled with high winds make the state particularly prone to the phenomenon.
Changing decisions
Shafer was one of about 20 researchers and agriculture leaders who attended a workshop on the drought index at the University of Oklahoma last month. The fact that the system can predict drought before it causes damage to plants is an advantage over other drought monitoring tools, he said.
Besides being a valuable tool for farmers and ranchers, Shafer said he expects the index could also help state officials predict where wildfire is likely to break out, he said.
Corey Moffet, a range scientist at the Sam Roberts Noble Foundation, said the tool, in combination with soil moisture data and weather forecasts, could give farmers a better idea of when to make certain decisions. For example, farmers growing cover crops could get a better idea of when to terminate those crops to preserve soil moisture, he said.
©2014 The Oklahoman. Distributed by MCT Information Services.
