SLOPE RESPONSE TO DECADAL AND CENTENNIAL SCALE CLIMATE VARIABILITY

Tree ring data from a grid of precipitation-sensitive sites in the American Southwest were used to reconstruct annual precipitation variability for the last 2000 years. Dendroclimatic reconstructions across the region indicate that climatic transitions have occurred on a regular basis for the past 2000 years with periodicities of ~74 and 44-years modulated by longer period variability. The most recent transition began a few years after 1905 AD and was associated with the largest precipitation shift (dry to wet) in the last 2000 years. Similar, albeit smaller, transitions, concurrent vegetation change and slope response occurred during the Little Ice Age. Larger shifts associated with major megadrought scale transitions appear to operate on timescales of approximately 450 years with earlier occurrences in the 700's, 1100's, and late-1500's. Dendrogeomorphic reconstructions from easily weathered slopes suggest that cyclic erosional behavior may be related to this decadal to centennial-scale climate variation across the region. A change to higher magnitude events in the 20th century and marked transitions from wet to dry conditions may be indicative of a climatic shift that has recently decreased surface vegetation cover, increased the likelihood of erosion of surface materials and possibly enhanced sediment supply which may well influence the geomorphic response of larger drainages in the region.