PUTTING THE RECENT PLUVIAL INTO CONTEXT: TREE-RING RECORDS OF MIDCONTINENTAL NORTH AMERICAN HYDROCLIMATE

Tree-rings in the Midwest have long been used to reconstruct the temporal and spatial variability of hydroclimate. Recently updated and newly developed ring-width records from Northeast Ohio show a strong secular increase in ring-width, in part driven by increasing precipitation to the region. Some tree species track this rise well, whereas others are losing their sensitivity as moisture continues to increase. A regional master dated back to 1680 CE shows a relatively dry interval of summer precipitation (pre-1880) coincident with the Little Ice Age and the pluvial starting over 100 years ago and continuing today. This series also includes marked dry intervals notably following the large-scale eruptions recognized in ice cores at 1695 and 1809. These intervals of summer drying are likely related to changing circulation patterns and storm tracks forced by strong cooling in the North Pacific.

We further explore the North Pacific temperature/ Midwest moisture linkage using a network of tree-ring series from Alaska and the West to reconstruct winter (JFM) Lake Erie levels. A well-verified model of lake levels is calibrated over the full observational record of monthly winter levels beginning in 1860 and provides a perspective of lake level variability back to 1600 CE. Over this interval, the highest levels are recorded in the last few years of the observational record (2019-2021) and the lowest during the Dustbowl years centered on 1934.

Two questions arise from these investigations of summer precipitation and winter lake levels. First, what are the mechanisms and circulation changes associated with volcanic cooling and how might their study be instructive in better understanding midcontinent hydroclimate? Secondly, since the summer drying in the early 1800s corresponds with major landscape changes associated with European Settlement in the region, did these changes perturb the hydrologic cycle facilitating the drying at this time? Related to this question, since the extremes of winter Lake Erie levels have occurred in the past 100 years after settlement, have the lake levels become more sensitive to climate as water storage in the basin has decreased and runoff has increased during a time of steadily rising precipitation?