Variations in precipitation in North America during the past 2000 years

We present a 2000-year pollen-based reconstruction of total annual precipitation (ANNP) for North America. Application of Local Indices of Spatial Association (LISA) permitted us to distinguish regional large-scale hydroclimate patterns from local site-specific conditions across North America during this time period. Century-scale filtered pollen-based reconstructions are more spatially coherent than unfiltered reconstructions, allowing for better identification of past hydroclimate patterns across North America. Similar spatial patterns dominated during both the ‘Medieval Warm Period’ (MWP; 950–1250 CE) and Roman Warm Period (RWP; 50 BCE–150 CE), although the MWP was generally drier than the RWP. In contrast, hydroclimate changes during Dark Ages Cold Period (DAC; 350–650 CE) and the ‘Little Ice Age’ (LIA; 1550–1850 CE) show opposing patterns across the western and eastern boreal region of North America. During warm periods, eastern and western boreal regions had similar moisture condition, whereas durin...