A 332-year reconstruction of Midwest droughts from tree-rings

The temporal variability and severity of pre-instrumental record droughts in the Midwest (Ohio, Illinois, and Indiana) are not as well understood as elsewhere in the United States. This study attempts to help fill the gap in Midwest drought knowledge by updating existing tree ring chronologies in Illinois and Ohio, and creating a new chronology in Indiana. Additionally the Atlantic Multi-Decadal (AMO), Arctic (AO), North Atlantic (NAO), Pacific Decadal (PDO), El-Nino Southern (ENSO) Oscillation's and the Pacific North American Pattern's (PNA) effects on radial tree-ring growth are examined. Standard dendrochronology methods are used to reconstruct the June, July, and August Palmer Drought Severity Index for Southern Illinois, Southern Indiana, and Northern Ohio. A composite regional chronology was also created using a nested Principal Component Analysis, in order to examine regional drought patterns. The chronology of trees sampled at Johnson State Nature Preserve in Ohio were the oldest (1680 sample depth), followed by Giant City State Park (1710 sample depth), and finally the Pioneer Mother's Memorial Forest's chronology in Indiana was the youngest (1870 sample depth). I found that the most recent meteorological droughts of 2012 and 1988 were not ranked as severe relative to historical droughts. These findings indicate that droughts could be potentially much more severe than in recent times, potentially causing greater damage to societies. Additionally the teleconnections that most influenced radial tree growth varied from site to site, indicating that the Midwest may be in a transition zone between various teleconnections. Further, my findings indicate that future droughts in this region are difficult to forecast using standard teleconnection indices, making it challenging for water managers to prepare for a drought of comparable severity to past droughts.