NORTH America's long-playing drought is over. But drought scientists warn that its challenge remains.
They note that a year of abundant rains will not necessarily repair the damage that half a decade's parching has done to dried-out fields and forests. Moreover, there is no guarantee that the drought won't return soon.
What's needed, such experts say, is a thorough assessment of measures used to ease the effects of drought to learn what worked and what didn't work.
According to a study of the drought by the American Meteorological Society, while severe drought is largely unpredictable, it is an expectable part of normal climate. Strategic planning to cope with drought when it hits, "has the potential to ease the impacts of future droughts," the society's statement says.
Meteorologist Donald A. Wilhite of the University of Nebraska at Lincoln notes that around two dozen states already have contingency plans. He says it's also important to take a hard look at the mix of federal programs. "Did the whole [federal] system work?," he asks. "I think we'll find that it didn't."
Dr. Wilhite warns: "Unless we go back and look ... [to see] what we have learned ... the tendency is that, the next time we have a drought, we repeat the mistakes."
One of those "mistakes" is to assume that drought is "abnormal" weather that is ended when "normal" rains return. In those terms, drought is over in the United States, except for an area in the northwestern part of the country. (See map above.)
Geographer William Riebsame of the University of Colorado at Boulder warns that this may be misleading, however. Asked if drought has ended with the wetter conditions, he says, "There's no way to say `no' to that question, climatologically." But, he adds, "there are long-term effects that are hard to assess."
Dr. Riebsame explains that a landscape that has dried out over several years cannot simply reabsorb water and recover. Reservoirs may refill quickly while soil moisture can remain dangerously low. The long-term parching of forests affects seedlings. Loss of wetlands affects waterfowl.
Riebsame notes that no one knows what happens when a whole ecosystem dries out. Any comment now on the drought's long-term effects, he says, "is speculation." Research is needed to help plan realistically for coping with extended drought.
The causes of major droughts also are not well understood. Basically, they reflect large-scale disruptions in the atmosphere's global circula- tion patterns.
One factor that affects those flow patterns and may sometimes be involved in North American droughts is the so-called El Nino phenomenon. This involves episodes of warmer-than-normal or colder-than-normal sea-surface temperatures in the eastern and central equatorial Pacific Ocean. Although El Ninos occur irregularly, a cold or warm episode is present in about 40 percent of all years.
According to the American Meteorological Society, warm El Ninos are related to drought in southwestern Africa, northeastern South America, central and northern India, and much of the western equatorial Pacific region. Cold El Ninos are linked to droughts in the southeastern United States and northeastern Mexico. These cold episodes are also involved in droughts in east-central Africa, central equatorial Pacific regions, southern India and Sri Lanka, and eastern South America.
Understanding such factors can sometimes help certain regions anticipate dry conditions even though major droughts generally are unpredictable. Computer models of the atmosphere can predict cold or warm El Ninos up to 15 months in advance. Also, drought tends to persist once it becomes established. Dried-out soils soak up more solar energy when they have less water to cool them by evaporation. If drought hits the central US in spring or summer, it is likely to persist for another three to six months.
However, even this limited predictability won't help a region cope with drought if it isn't prepared for it, drought scientists warn. Riebsame points out that 1988 - the worst year of the recent drought period - was a bigger disaster than hurricanes Hugo or Andrew. It affected 40 percent of the United States and involved estimated direct costs and economic losses of about $40 billion. Yet this hasn't spurred the kind of advanced planning that more dramatic disasters such hurricanes or earthquakes encoura ge.
Wilhite explains that a basic reason for this neglect at the federal level is that responsibility for drought planning is split among 16 agencies with differing missions. What is needed, he says, is a coordinated effort with a single lead agency in charge.
Wilhite says he is cautiously hopeful that such coordination will begin to happen. He notes that there is growing public awareness that climate is variable and that drought is an expectable event. He also notes that international agreements for environmental cooperation require the United States to work with other nations in drought planning.
"It's a topic that's come into its own in the past couple of years," Wilhite says.