Nonstationary Teleconnections Over North America Revealed in Paleoclimate Data Assimilation Reconstructions Spanning the Last Millennium

Abstract Modes of climate variability, such as the El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multi‐decadal Oscillation (AMO), have been shown to have large impacts on North American hydroclimate through their atmospheric teleconnections. However, short instrumental records limit our ability to examine the long‐term stability (or stationarity) of hydroclimate teleconnections. Here, we use two last millennium (LM) paleoclimate data assimilation (DA) products to assess the stationarity of hydroclimate teleconnections over two key regions: the southwestern U.S. and Lower Mississippi River basin. Moving correlations between climate indices and regional hydroclimate expose highly nonstationary regional hydroclimate teleconnections with significant periodic variations on multi‐decadal and multi‐centennial timescales. Although limitations of the DA products prohibit a robust analysis of climate mode intensity, consistent sea surface temperature (SST) patterns between DA products during strong and weak teleconnection periods suggest that changing teleconnection strength is driven by the changing relationships between climate modes over the LM. Although our results are sensitive to proxy availability, the DA techniques provide novel insight into the nonstationarity and long‐term variability of North American hydroclimate teleconnections. This work provides a baseline for teleconnection behavior from DA products, which is potentially valuable for decadal prediction.