As the Eastern United States continues to suffer from this summer's record-breaking drought, scientists are scrambling to find ways to better understand what happens to forests, rangeland and crops during such extended dry spells. Now, researchers at The University of Montana are offering a new tool to identify what areas are first affected by a lack of rainfall and keep watch on regions hardest hit.
UM researchers Steven Running, a forest ecologist, and Lloyd Queen, a remote-sensing specialist, created a new "drought map" using National Oceanic and Atmospheric Administration (NOAA) satellite data. The satellites relate the ground surface temperature with a measurement of vegetation greenness across the United States, and hot surfaces tell the scientists where areas are succumbing to drought.
States currently hard-hit by the drought identified in the new maps include; Maine, Vermont, eastern New York, central South Carolina, western North Carolina and southeast Georgia. Many of these drought-affected areas aren't visible when looking at currently available satellite drought maps because the current maps look only at vegetation greenness, Queen said. The satellite drought images also show when crops are under stress due to drought, and the UM team is working cooperatively with six other universities in the upper Midwest and Northern Rockies to provide drought image maps to farmers and ranchers.
The new drought maps compare current surface temperature measurements to average surface temperatures over the last 10 years and show whether an area has a normal, low, medium or high drought index. The method works because when the sun's energy hits the land surface, some energy is used to evaporate water and some goes to heating up the ground.
"The less water available to evaporate, the more the ground heats up," Running said. "So even if a forest looks green from a satellite view, it may be under considerable stress due to lack of water."
Using this logic, Queen said, the researchers measure how much moisture stress a canopy is experiencing.
"If the canopy is vigorous, healthy, active and well-watered, then it's going to be comparatively cool, and once that vegetation starts to become water-stressed, it's going to become hotter," Queen said.
An updated map, produced within hours of the time the satellite takes the temperature and greenness measurements, will be available every 10 days, Running said. The new maps will enable those who are worst affected by drought to take preventative measures, he said. With a heads-up on a coming drought, ranchers can pull cattle from drought-affected areas, farmers can irrigate sooner and policymakers can be better informed to make decisions concerning range and forest management.
"The same drought index transfers directly to fire potential and will tell fire managers where fire potential will develop," Running said. Since 1996, the Montana team has offered the satellite temperature/greenness measurements to the U.S. Forest Service to be included in the National Fire Danger Rating System, which is designed to help fire managers assess potential fire hazards.
Running and Queen developed the new mapping system to be used with an instrument aboard NASA's Terra satellite, set for launch in fall 1999. The new instrument will provide even more precise measurements and enable even more accurate drought and fire potential maps. The current drought-maps can be found on the Internet at: http://eostc.umt.edu/Forestry/Products/showSMIByYear.asp?year=1999.
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