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July-Aug 2002

Understanding drought: Can society prepare itself for prolonged dry periods?

The ongoing drought in the West has taken a toll on Lake Granby. (Photo by Carlye Calvin.)


Drought haunted the childhood of Bob Harriss. Now the director of the Environmental and Societal Impacts Group, Bob grew up on a South Texas ranch in the mid-1950s at a time when rainfall was so scarce that parts of the Rio Grande went dry. He can remember watching farmworkers harvesting fish that were trapped in the remaining small pools of water. Desperate to save their herds, ranchers burned thorns off cactuses, which were the only source of moist food for the dying cattle.

The drought's toll was so high that Bob's family eventually moved its ranching business to Florida in search of more dependable rainfall.

"Those were pretty dramatic events for a kid," he recalls.

Small wonder that Bob retains a keen interest in drought. He researched the issue as a professor at Texas A&M University, and now he works with ESIG's Olga Wilhelmi on strategies for reducing the impact of drought.

Another ESIG scientist, Heidi Cullen, is looking at the ways that a severe drought is affecting Afghanistan and other areas of Central and Southwest Asia. These studies are taking on a wider relevance as several key regions in the world, including the Rocky Mountain West, are enduring a severe dry spell that is lowering reservoirs and withering crops.

Such research complements the well-known work of ESIG's Mickey Glantz, who advises public policy officials overseas on strategies to lessen the impact of drought in vulnerable regions. "I think drought is the sleeper issue of the 21st century for urban areas," Mickey says. "As water quantity goes down, quality will go down with it."

And drought research at NCAR is hardly limited to ESIG. Kevin Trenberth (CGD) studies climate patterns that can lead to drought as well as destructive storms, and how global climate change is affecting those patterns˛to the cost of society.

In a recent op-ed article in The Denver Post, Kevin warned: "And so global warming promotes drying and droughts. And then the droughts promote heat waves and wildfires. But the moisture that goes into the atmosphere [because of global warming] does not disappear. It gets carried away by winds, and gathered into storms often hundreds of miles away."

A global problem

Drought can strike virtually any region, and studies have shown that it affects more people than any other type of natural disaster. It wipes out crops, spurs wildfires, dries up water sources, and sickens or even kills people through associated heat waves.

Bob Harriss got an unforgettable lesson in drought as a boy growing up on a Texas ranch. (Photo by David Hosansky.)

Severe dry periods have other, lesser-known effects as well. While Bob was helping to oversee drought research in the late 1990s for the U.S. National Assessment of the Potential Consequences of Climate Variability and Change, he learned about the shearing and breaking of underground water pipes during a drought in Dallas, which cost the city considerable amounts of precious water. The pipes broke because the soil had become so dry that it began to shrink. Another drought-related problem that Bob encountered during his work in Texas: watered city lawns became havens for insects that had fled the dry landscapes of outlying areas.

"What was most interesting and surprising to me was the subtle impacts of drought that I had not seen in the published literature,"Bob recalls.

Scientists do not yet understand all the dynamics of drought, although research shows that El Niño triggers dry conditions in some parts of the world (such as India, Indonesia, and northeast Brazil), while La Niña causes drought in other places, such as eastern equatorial Africa and the central Pacific. Land-air interactions also play a role. Once the ground is dry, it returns the Sun's heat into the atmosphere more readily—and, if vegetation withers, even more heat is reflected into the atmosphere. This tends to perpetuate the dry conditions.

Even when rainfall and winter snows return to normal, years may pass before lakes and reservoirs are fully replenished. This is why water managers in Boulder and Denver are bracing for a prolonged period of tight water supplies.

Suffering in Asia

Nowhere has drought struck harder in recent years than in Afghanistan and other countries in Central and Southwest Asia. Some 60 million people have been affected by a severe lack of rainfall that started in the late 1990s, causing water shortages, crop failures, and, ultimately, widespread hunger˛all in a region already suffering from political turmoil and violence.

Because the region is so dependent on agriculture, ESIG's Heidi Cullen says: "A drought on that level really affects all sectors of the society."

Heidi began studying the region last year as a postdoctoral research scientist at the International Research Institute for Climate Prediction in New York. One of her goals is to better understand the causes of drought in Central Asia, so residents of the region, as well as international relief agencies, can prepare for dry periods. "If we understand the dynamics, then we‚re that much closer to predictability."

Heidi believes that the droughts may be triggered by warming waters in the Indian Ocean, which cause a high-pressure system to sit over Central Asia and block moisture coming in from the Mediterranean. Scientists think that La Niña also plays a role, although they remain unsure of where it fits in.

The current drought is the worst in observational records that date back to the 1950s, she says. The soil has been depleted of moisture and the crops "have been hit hard." Although rainfall began returning to normal levels during the spring, it may take years to fully replenish the soil.

The drought comes atop a trend of declining water availability resulting from decades of unsustainable water practices. Glacial melt, caused by warmer temperatures during the last several years, suggests that global warming may also be a factor in the region‚s hydrologic balance. "It's a big, long-term warning signal," Heidi says.

Dry conditions in Nebraska

Olga Wilhelmi is studying drought conditions closer to home. Using Geographic Information Systems (GIS) and remote sensing technology, she is mapping out vulnerability to drought in Nebraska in order to help planners prepare for inevitable dry periods.

Olga Wilhelmi and Heidi Cullen study the societal effects of drought. (Photo by Carlye Calvin.)

"The ultimate goal is to treat drought as a normal part of climate and not as a natural disaster," she explains. "If we know that it is a natural part of climate and plan accordingly, the impacts of the drought will be less."

Even though Nebraska has a long history of drought, the state typically has focused on recovering from drought instead of preparing for it. This approach began to shift in 1998, when the National Drought Mitigation Center recommended that the state revise its drought plan by putting more emphasis on lessening the impacts of drought.

To this end, Olga and the University of Nebraska‚s Donald Wilhite incorporated data about climate, soil types, land use, and access to irrigation to create a map of Nebraska that pinpoints agricultural regions vulnerable to drought. The highest risk areas were found to be nonirrigated croplands and rangelands on sandy soils located in regions likely to suffer from low precipitation. In a paper they wrote for Natural Hazards, the two researchers suggest that farmers in those regions adjust their cropping patterns to maximize yields during years of normal precipitation and minimize losses during dry years. •David Hosansky





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Drought in Asia

Background on drought issues

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Edited by David Hosansky, hosansky@ucar.edu
Prepared for the Web by Carlye Calvin
Last revised: Fri Apr 12 17:08:40 MST 2002