March 3, 2004


KU researchers develop method to provide early, reliable drought detection

LAWRENCE -- A farmer checking soil moisture squeezes dirt in his hand, opens it and sees whether the dirt's balled up. He works it between thumb and forefinger to see whether it will ribbon.

The scientific approach is less hands-on. A meteorologist combines temperature, humidity, precipitation and other data into "water-budget models" to assess how moist or dry the soil is.

Other scientists monitor soil moisture from 500 miles above the earth by analyzing satellite data.

Three University of Kansas researchers who are combining satellite data with a simple water-budget model believe that their approach may provide early and reliable warning of approaching drought.

Such information is of potential use to farmers in deciding when to irrigate and to traders who deal in grain futures. But it's especially vital, the scientists said, to governments that need to supply food in a timely manner to areas where drought could cause widespread starvation.

The scientists discussed satellite- and ground-based drought detection in an article published recently in the journal Remote Sensing of Environment.

They are Sun Park, a postdoctoral fellow at the Kansas Biological Survey and the Kansas Applied Remote Sensing Program at KU; Johan Feddema, associate professor of geography; and Steve Egbert, assistant professor of geography.

Satellites eye huge swaths of land as they orbit the earth, far more than any staff of meteorologists at a climate station could.

One method used by the KU scientists in their drought study involved reading the amount of heat coming off the earth. That's reflected by how much thermal infrared radiation a patch of ground is emitting, Feddema said.

Another drought indicator is wilted vegetation. KU's Kansas Applied Remote Sensing program, or KARS, monitors the "greenness" of vegetation to determine how water-stressed it is. A weekly Green Report from KARS makes those findings available to subscribers.

The trouble is that plant wilt happens late in a drought, said Feddema.

"With our method, we hope to be able to give more advanced notice -- two to three weeks -- of a drought's onset," he said.

He said that surface soil temperature provides an earlier warning of drought than wilt because it is such a sensitive indicator of the moisture content of the subsurface.

"Think of wet and dry sand on the beach," he said.

Besides weather, two factors govern how quickly or slowly a piece of ground scorches.

One is a field's water-holding capacity, or WHC. The WHC is determined by such elements as the depth of soil and the space between its grains.

The other factor is the type of soil in the field -- clay, loam or sand -- because that determines runoff. Park and his colleagues refer to this factor as hydrological soil type, or HST.

In the article, the researchers report that WHC is more important than HST in governing the speed of a drought's onset.

Feddema said that the novelty of the study led by Park is that it linked examination of satellite data to soil information and an extremely simple weather model in determining how much moisture would be in the soil.

The weather model required only two pieces of information, about rainfall and temperature. That makes it potentially useful in countries where there's a shortage of weather data.

"Detailed meteorological information isn't available in many countries," Park said.

Most scientists who have tried to predict drought use satellite data alone or, if they have combined the data with ground-based weather information, they usually use more complicated weather models.

Those models typically do not include both rainfall and temperature data, Feddema said, adding that "you can't say much about drought without using both."

Those who invest in grain futures are the most common users of satellite drought-detection capabilities, but Feddema's interests are less commercial than humane.

Feddema said that a timely forecast of drought is especially important in countries like Africa, where crop failure can mean starvation.

"If we want to provide international aid to such places," Feddema said, "a few weeks' notice of a drought can be the difference between giving aid or being too late."



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