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CR prepress abstract   -  DOI: https://doi.org/10.3354/cr01637

Tree-ring-reconstructed late-summer moisture conditions, 1546 to present, northern Lake Michigan, USA

Scott M. Warner*, Samantha J. Jeffries, William A. Lovis, Alan F. Arbogast, Frank W. Telewski

*Corresponding author:

ABSTRACT: Drought can affect even humid regions like northeastern North America, which experienced significant, well-documented dry spells in the 1930s, 50s, 60s, and 80s, and proxies tell us that in the years before instrumentally recorded climate, droughts could be even more severe. To get a more complete picture of pre-recorded climate, the spatial coverage of proxy-based climate reconstructions must be extended. This can better put in context past, current, and future climate, and it can lend anthropological and historical insights. With regard to tree-rings as climate proxies, however, there is increasing evidence that relationships between tree-growth and climate can be inconsistent over time, in some cases decreasing the utility of tree rings in the representation of climate. We developed a chronology from white cedar Thuja occidentalis tree-ring widths for the period 1469—2015 C.E. with which we modeled the relationship between growth and July—September moisture conditions (Palmer Z Index). The relationship was consistent across the period of instrumentally recorded climate, 1895-present, and the model explained 27% of variability. Therefore, we used the model to reconstruct July–September moisture conditions from 1546-2014. We found the most variable century to be the 20th, the least the 18th. The severest decade-scale droughts (≤ 0.75 SD from mean) occurred in the 1560s, 1600s/10s, 1630s, 1770s/80s, 1840s, and 1910s/20s, the severest pluvials (≥ 0.75 SD) in the 1610s/20s, 1660s/70s, and the 1970s/80s. The occasional occurrence of severe droughts throughout the reconstruction, increasing variability in the 20th century, and expected climate-change-enhanced late-summer drought, portend a future punctuated with severe droughts.