Reconstruction of Precipitation in North America Over The Last Millennium Using Multiple Proxies

Past work in making long-term reconstructions of precipitation and deriving estimates of hydro-climatic variability from those reconstructions was based largely in tree-ring proxy records. More recent work that was focused on the Pacific Northwest region of the United States employed oxygen isotope data derived from lake sediments to reconstruct winter precipitation for the last 1500 y and yielded that wet conditions prevailed in winter during the Medieval Climate Anomaly (MCA) period (900-1300 AD) and drier winters prevailed during the Little Ice Age (LIA) period (1450-1850 AD), which somewhat contradicted findings derived from tree-ring records alone. The work that we present here exploits this notion that multiple paleo-climate proxies are required for robust long-term reconstructions of precipitation. We are making a precipitation reconstruction for approximately the last millennium over a large area of land in North America spanning from approximately central Mexico to southern Canada. A Regularized Expectation Maximization (RegEM) algorithm is employed, with some modifications aimed at accommodating use of multiple types of proxy record. Some early results from this work will be presented.