A Millennial Scale Tree-Ring Precipitation Reconstruction for the Tavaputs Plateau, Northeastern Utah

Despite the extensive network of tree-ring sites in western North America, relatively few moisture sensitive chronologies document past climatic variability before AD 1000 and thus conditions prior to and throughout the Medieval Climate Anomaly. We developed a tree-ring chronology extending back to 323 BC by taking advantage of the combination of extraordinary tree longevity and subsequent preservation of remnant Douglas fir (Pseudotsuga menziesii) from the Tavaputs Plateau in northeastern Utah. Using this chronology we reconstructed precipitation variability for the Tavaputs Plateau using PRISM generated climate data for calibration. The regression model accounts for 70% of the variance of precipitation for the 1917-2005 calibration period. Our reconstruction agrees well with other tree-ring reconstructions of moisture related variables in the region for the period of overlap (AD 1400-2000). Similar to many other proxies of past drought in the west, the medieval period is marked by several prolonged dry periods, especially prominent in the mid AD 1100s and late 1200s. These droughts, however, are exceeded both in length and magnitude by droughts occurring in prior and subsequent centuries. Particularly severe is a drought in the AD 500s that surpasses in magnitude any drought during the last 1800 years. While reflected in nearby newly constructed long tree-ring chronologies, the 500s drought does not appear as prominent in other tree-ring reconstructions in the region. Anomalous conditions do occur during the medieval period, consisting of a marked decrease in the frequency of decadal and short-term to annual extremes, both wet and dry. This lack of extreme conditions accompanied the height of Fremont agriculturist occupation of the Tavaputs between AD 1000 and 1200. The increase in the frequency of decadal and annual extremes after 1200 could have had a detrimental impact on Fremont agriculture in the study area.