Because winter precipitation has the strongest influence on annual tree growth, previous large-scale, long-term tree-ring reconstructions of the region's precipitation history had focused only on the winter rainy season.
"Now we see wow the summers were dry, too," she said. "That has a big impact."
The team's research report, "North American monsoon precipitation reconstructed from tree-ring latewood," is scheduled for publication March 11 in Geophysical Research Letters, a journal of the American Geophysical Union.
Additional UA co-authors are David M. Meko, Holly L. Faulstich, Carlos Carrillo, Ramzi Touchan, Christopher L. Castro and Steven W. Leavitt. Co-author David W. Stahle is from the University of Arkansas in Fayetteville.
The National Science Foundation, the National Oceanic and Atmospheric Administration and the U.S. Environmental Protection Agency supported the research.
"In the Southwest, the winter precipitation is really important for water supply. This is the water that replenishes reservoirs and soil moisture," Woodhouse said. "But the monsoon mediates the demand for water in the summer."
Until recently, most tree-ring researchers, known as dendrochronologists, have looked at the total width of trees' annual rings to reconstruct past climate. Few teased out the seasonal climate signal recorded in the narrow part of the growth ring laid down in late summer known as latewood.
To figure out the region's past history of monsoon precipitation, the scientists needed to measure latewood from tree-ring samples stored in the archives of the UA Laboratory of Tree-Ring Research and go into the field to take additional samples of tree rings.
The team looked at annual growth rings from two different species, Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa) throughout the weather forecast region called North Amer
|Contact: Mari N. Jensen|
University of Arizona