Patterns and sources of multidecadal oscillations in drought‐sensitive tree‐ring records from the central and southern Rocky Mountains

[1] Tree-ring records spanning the past seven centuries from the central and southern Rocky Mountains were studied using wavelet analysis to examine multidecadal (>30–70 yr) patterns of drought variation. Fifteen tree-ring series were grouped into five regional composite chronologies based on shared low-frequency behavior. Strong multidecadal phasing of moisture variation was present in all five regions during the late 16th century megadrought. Consistent oscillatory modes in the 30–70 yr domain persisted until the mid-19th century in two of the five regions, and wet-dry cycles were apparently synchronous at some sites until the 1950s drought. The 16th/17th century pattern of severe multidecadal drought followed by decades of unusually wet conditions resembles the 1950s drought and post-1976 wet period. The 16th century megadrought, which may have resulted from coupling of a decadal (20–30 yr) Pacific cool phase with a multidecadal warm phase in the subtropical North Atlantic, marked a substantial reorganization of climate variation in the Rocky Mountain region. INDEX TERMS: 1812 Hydrology: Drought; 1833 Hydrology: Hydroclimatology; 1854 Hydrology: Precipitation (3354); 9350 Information Related to Geographic Region: North America; KEYWORDS: drought, treerings, multi-decadal variability, western U. S., Pacific Decadal Oscillation, Atlantic Multidecadal Oscillation. Citation: Gray, S. T., J. L. Betancourt, C. L. Fastie, and S. T. Jackson, Patterns and sources of multidecadal oscillations in drought-sensitive tree-ring records from the central and southern Rocky Mountains, Geophys. Res. Lett., 30(0), XXXX, doi:10.1029/2002GL016154, 2003.