Abstract
Abstract. A synthesis of 93 hydrologic records from across North and Central America, and adjacent tropical and Arctic islands, reveals centennial to millennial trends in the regional hydroclimates of the Common Era (CE; past 2000 years). The hydrological records derive from materials stored in lakes, bogs, caves, and ice from extant glaciers, which have the continuity through time to preserve low-frequency ( > 100 year) climate signals that may extend deeper into the Holocene. The most common pattern, represented in 46 (49 %) of the records, indicates that the centuries before 1000 CE were drier than the centuries since that time. Principal component analysis indicates that millennial-scale trends represent the dominant pattern of variance in the southwestern US, northeastern US, mid-continent, Pacific Northwest, Arctic, and tropics, although not all records within a region show the same direction of change. The Pacific Northwest and the southernmost tier of the tropical sites tended to dry toward present, as many other areas became wetter than before. In 22 records (24 %), the Medieval Climate Anomaly period (800–1300 CE) was drier than the Little Ice Age (1400–1900 CE), but in many cases the difference was part of the longer millennial-scale trend, and, in 25 records (27 %), the Medieval Climate Anomaly period represented a pluvial (wet) phase. Where quantitative records permitted a comparison, we found that centennial-scale fluctuations over the Common Era represented changes of 3–7 % in the modern interannual range of variability in precipitation, but the accumulation of these long-term trends over the entirety of the Holocene caused recent centuries to be significantly wetter, on average, than most of the past 11 000 years.
Highlights
Hydroclimate extremes characterize the Common Era (CE; the past two millennia) across North America (Cook et al, 2007; Woodhouse and Overpeck, 1998) and other parts of the Northern Hemisphere (Ljungqvist et al, 2016)
Using data binned by century, we evaluate the patterns associated with commonly referenced periods such as the MCA from 800 to 1300 CE (1150–650 BP) and the Little Ice Age (LIA) from 1400 to 1900 CE (550– 50 BP), but we describe other first-order hydroclimate trends represented by the data
Because few data exist for some regions such as the southeastern US (Fig. 1), the absence of any patterns may be a function of data availability
Summary
Hydroclimate extremes characterize the Common Era (CE; the past two millennia) across North America (Cook et al, 2007; Woodhouse and Overpeck, 1998) and other parts of the Northern Hemisphere (Ljungqvist et al, 2016). Wet and dry conditions shifted at annual to multi-decadal scales (Fye et al, 2003; Pederson et al, 2011; Woodhouse et al, 2009), with notable periods of “mega-drought.”. The Medieval Climate Anomaly (MCA) period (800–1300 CE), in particular, included several decades-long droughts that have been widely analyzed to assess the underlying mechanisms
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