ScienceDaily (Sep. 1, 2000) — NASA has a new tool designed to keep a close watch over our plants. What we see in the reflection of the vegetation may help researchers do a better job of monitoring and, one day, predicting periods of drought.

A new Multi-spectral Drought Index measures the impacts of too little water or too much rainfall on vegetation. The index will also be used to verify other existing drought-monitoring products.

"What makes this data set unique is its unprecedented detail, which provides a resolution four times that of current drought prediction maps, and it is based on a 20-year data record," said Compton Tucker, the research scientist leading the project at NASA's Goddard Space Flight Center, Greenbelt, MD.

The new Multi-spectral Drought Index utilizes and improves the data from the Normalized Difference Vegetation Index (NDVI) and shows deviations from average vegetation levels. The NDVI is an index created by Tucker 20 years ago to measure the absorption and reflectance of sunlight by plants.

The NDVI data sets show the greening and browning of plants as they relate to seasonal changes and conditions such as drought or abundant rainfall. The data is gathered by the polar-orbiting satellites built by NASA and operated by the National Oceanic and Atmospheric Administration.

The satellites measure the reflectance and absorption characteristics of plants at different wavelengths in the electromagnetic spectrum. The data are registered in numerical form, and translated by researchers into monthly maps of vegetation color changes, which in turn indicate how much soil moisture is available to plants. Since the global data set spans a 20-year time period, researchers can better determine what are "normal" levels of plant growth, and what are unusually high or low levels.

Sunlight can either be absorbed by leaves and needles or scattered within and among them. By using red and infrared wavelengths in the spectrum, multi-spectral imaging measures the absorption rate of sunlight and identifies levels of chlorophyll generated in vegetation. When more sunlight is absorbed, higher levels of chlorophyll are generated in vegetation showing plant growth. Conversely, when a plant is stressed from lack of fertilizer or water, it will limit its chlorophyll production compared to healthy plants.

"The new Multi-spectral Drought Index is used to generate better vegetation anomaly maps than before," according to Tucker. Light brown on the drought map means there's diminished plant growth, green on the map indicates a higher than average plant growth.

A map generated for July 2000 indicated a drought in the western United States. "The data clearly shows why we're having wildfires," Tucker said. "Soil conditions are dry, and the diminished vitality of vegetation indicates that."

Many drought products are based on water availability in soils. The new index maps integrate climate variables such as soil moisture, temperature and precipitation, and show how vegetation responds to environmental conditions around the world.

"The bottom line is that the new Multi-spectral Drought Index reflects the actual environmental conditions of the vegetation, and at a much higher resolution than previously available, which will be helpful in supplementing and validating the NOAA drought forecast maps," Tucker said.

The first data sets covering North America and Africa and are currently available at:

http://earthobservatory.nasa.gov/Drought

Images and animations are available at: http://svs.gsfc.nasa.gov/imagewall/drought.html

Complete data sets including images from all continents are expected to be released to the scientific community early next year. This research is done in support of NASA's Earth Science Enterprise, Washington DC. The Enterprise is dedicated to the long-term study of how human-induced and natural changes affect our global environment. More information about the Enterprise can be found at: http://www.earth.nasa.gov

Adapted from materials provided by NASA/Goddard Space Flight Center.

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