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Abstract
Analysis of daily scale climate observations alongside sub-annual tree-ring data offers new potential for contextualizing climate change in the Great Lakes region. This pilot study combined daily observations from a high-quality station record with a co-located chronology of Pinus resinosa latewood width at Lake Itasca, Minnesota. We evaluate trends in observational data and use multiple methods to compare day-wise aggregated climate observations with tree rings over the eleven-decade common period. The Itasca record exhibited strong increases in warm-season precipitation, minimum temperature in all seasons, and lengthening of the freeze-free season. Correlation analyses verified a strong, multi-month warm-season precipitation response in Pinus resinosa latewood width. Distinct from previous work, daily data analyses were used to fingerprint an ~2-week period starting in late July when rainfall variability was historically a major control on interannual tree growth. Climatologically, the timing of this subseasonal critical climate period corresponds with a relative minimum in mean midsummer precipitation. Since the 1980s, the latewood correlation with midsummer rainfall has vanished, and the seasonal-scale rainfall response diminished considerably. This result, new for Pinus resinosa in Minnesota, is consistent with studies showing a declining relationship between tree growth and drought in the Midwest United States. Further attribution analyses emphasizing daily-scale phenomena are needed to elucidate mechanisms responsible for the tree-growth response to variability, change, and extremes in climate throughout the Great Lakes region, where the biophysical and socioeconomic impacts of climate change are multifaceted issues of increasing urgency.
Highlights
Climate change in the Great Lakes region is clearly identifiable in observational data and model projections (Hayhoe et al, 2010; Andresen et al, 2012; Cook et al, 2020)
Increasing trends in precipitation were found in every season and in every month except for January at Itasca State Park (ISP), the strongest increases were found in September, October, and the SON season (Supplementary Figure 1)
Large increases in minimum temperature were found in every season and month except February, April, October, and November (Supplementary Figure 2). These increases in precipitation and minimum temperature from the ISP station are consistent with the broad scale spatial pattern of trends toward warmer and wetter warm-season conditions in the Great Lakes region (Figures 1D,E)
Summary
Climate change in the Great Lakes region is clearly identifiable in observational data and model projections (Hayhoe et al, 2010; Andresen et al, 2012; Cook et al, 2020). Most studies investigating tree growth-climate relationships in the Great Lakes region have used monthlyaggregated climate data and total ring-width It is unknown if the mechanisms underlying the fading drought signal may be better understood by evaluating climate and growth relationships at multiple timescales, including those that operate at the daily to biweekly timescales which can be obfuscated by time and space aggregation to monthly, seasonal, and regional scales
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