RAPID CITY -- Based on past droughts in this region, the current drought in the West could easily last another three to five years, National Weather Service expert Matt Bunkers said Tuesday.

Bunkers, along with other scientists speaking at a hydrology conference in Rapid City, said that droughts in the West River region typically last 10 years or more.

"It's difficult to know exactly what's going to happen this year, but I would bet that over the next three to five years, we will tend to be drier, just by observing the past," Bunkers told more than 150 scientists, government agency officials, civic representatives and students at the third annual Western South Dakota Hydrology Conference.

Bunkers, science and operations officer at the NWS's Rapid City office, said that even in the past century, dry periods lasted from 1930 to 1940, from 1949 to 1961 and from about 1980 to 1990.

Bunkers said after his presentation that 10-year drought cycles prevail in western South Dakota, compared with five-year drought cycles farther east.

Bunkers and Dennis Todey, state climatologist based at South Dakota State University in Brookings, said the current drought, although severe, is not as severe nor nearly as long as some earlier droughts that gripped this region.

Todey said part of the reason that the current drought seems so severe is that it came on the heels of the soggy 1990s, the wettest period in the area since at least the 1920s.

Of course, that is little comfort for farmers, ranchers, water system managers and residents trying to keep lawns green in western South Dakota over the past five years.

Bunkers said a study of April-through-October (the growing season) precipitation in the region shows that Rapid City had 15.37 fewer inches of precipitation than average for the five-year period from 2000 to 2004.

Other sites below average for the five-year period included Colony, Wyo., 21.59 inches below average; Camp Crook, 5.65 inches below average; Gillette, Wyo., 9.18 inches below average; Hot Springs, 14.4 inches below; Cottonwood, 10.27 inches below; and Newcastle, Wyo., 5.4 inches below.

Bunkers said dramatic fluctuations are the norm for this area. During the wet 1990s, Rapid City was above the average amount of precipitation by 13.99 inches.

During the last 40-year period beginning in the early 1960s, the region had average growing season rainfall about 2 inches above that of the previous 40 years, Bunkers said.

But he said that upward trend probably won't continue. "It is likely that over the next 20 years, we'll see the average come down."

Bunkers, Todey and Dan Driscoll, hydrologic studies chief for the U.S. Geological Survey office in Rapid City, all cited tree-ring studies that indicated even longer lasting droughts than the dust bowl drought of the 1930s. A drought nearly as severe as the Dust Bowl years lasted from about 1840 to the 1860s, according to the tree-ring data.

Other multi-decade dry periods came in previous centuries.

"It's been well documented that the severity and extent of previous droughts have far exceeded the current conditions," Driscoll said. "Planning for a worst-case scenario may be the way to go for our water managers."

Todey said some studies indicate the region is due for another multi-decade drought.

"Will another one occur?" Todey asked. "Yes. But we don't know when."

Meanwhile, there is some reason for hope, at least in the short term. The NWS forecast now calls for a chance of cooler-than-average temperatures and above-average precipitation in South Dakota this summer.

But Bunkers, Todey and Driscoll all said one year of above-average rainfall wouldn't break the drought. Bunkers said aquifer levels don't begin rising until about a year after a wet period begins.

All three said water managers and other officials should prepare for drought because it is inevitable in this area.

Todey drought cycles are not regular. "We must always be prepared for drought because we live on the plains. It is not going to change. It will come back."

Bunkers said a drought as severe and as long-lasting as the 1930s drought could pose even more problems for the region because of the increased population and increased demand on water resources now.

"When we have a period when we have a lot of rain, we can't use it like there's no tomorrow," Bunkers said. "We need to really be thinking about the future."

Contact Steve Miller at 394-8417 or steve.miller@rapidcityjournal.com