Scientists see drought lasting several decades

Friday, Feb. 14, 2003 | 9:35 a.m.

Scientists believe the five-year drought that has gripped the West could continue for decades, according to research published this week in a scientific journal.

The report that appeared in the journal Geophysical Research Letters refers to a study of how ocean temperatures are linked to tree ring records dating back thousands of years.

It suggests that the current drought could be the beginning of a much longer "megadrought."

Megadroughts can last as long as 40 to 70 years, according to the report.

One such drought plagued the North American continent in the 1500s, scientists said.

Scientists from the U.S. Geological Survey, the University of Wyoming and Middlebury College participated in the study.

"In the current context of ocean climate, the current drought should give water and other resource managers in the Rockies and in the Southwest little cause of optimism," said Julio Betancourt of the USGS.

The study relies on an idea that regional climate is linked in complicated ways to changing ocean temperatures, Betancourt said.

Interactions between changing tropical Pacific Ocean currents and northern Atlantic Ocean sea surface temperatures play pivotal roles in the North American climate, he said.

The scientists discovered that Pacific Ocean sea surface temperatures tend to shift on cycles of 20 to 30 years, he said. The conditions can shift abruptly.

"For example, in 1946, the tropical Pacific went cold for a decade and the Southwestern U.S. climate went dry, producing the 1950s drought," Betancourt said. "And in 1976, the tropical Pacific got warm, and the Southwest had a prolonged series of wet winters."

Betancourt and Thomas Swetnam of the University of Arizona Laboratory of Tree-Ring Research previously reported that tree ring data from the 1950s was linked to a drought that lasted from 1942 to 1972 in the Southwest.