NOAA/WDS Paleoclimatology - Maxwell - Babler State Park - CYOV - ITRDB MO082

Our understanding of the natural variability of hydroclimate before the instrumental period (ca. 1900 CE in the United States) is largely dependent on tree-ring-based reconstructions. Large-scale soil moisture reconstructions from a network of tree-ring chronologies have greatly improved our understanding of the spatial and temporal variability in hydroclimate conditions, particularly extremes of both drought and pluvial (wet) events. However, certain regions within these large-scale network reconstructions in the US are modeled by few tree-ring chronologies. Further, many of the chronologies currently publicly available on the International Tree-Ring Data Bank (ITRDB) were collected in the 1980s and 1990s, and thus our understanding of the sensitivity of radial growth to soil moisture in the US is based on a period that experienced multiple extremely severe droughts and neglects the impacts of recent, rapid global change. In this study, we expanded the tree-ring network of the Ohio River valley in the US, a region with sparse coverage. We used a total of 72 chronologies across 15 species to examine how increasing the density of the tree-ring network influences the representation of reconstructing the Palmer Meteorological Drought Index (PMDI). Further, we tested how the sampling date and therefore the calibration period influenced the reconstruction models by creating reconstructions that ended in the year 1980 and compared them to reconstructions ending in 2010 from the same chronologies. We found that increasing the density of the tree-ring network resulted in reconstructed values that better matched the spatial variability of instrumentally recorded droughts and, to a lesser extent, pluvials. By extending the calibration period to 2010 compared to 1980, the sensitivity of tree rings to PMDI decreased in the southern portion of our region where severe drought conditions have been absent over recent decades. We emphasize the need of building a high-density tree-ring network to better represent the spatial variability of past droughts and pluvials. Further, chronologies on the ITRDB need updating regularly to better understand how the sensitivity of tree rings to climate may vary through time.

我们对器测时期（美国约公元1900年）之前水文气候自然变率的认知，在很大程度上依赖于基于树轮的气候重建结果。依托树轮年表网络构建的大尺度土壤湿度重建结果，极大地提升了我们对水文气候条件时空变率的认知，尤其是干旱与多雨（湿润）事件的极端情况。然而，美国此类大尺度网络重建中，部分区域仅依靠极少量树轮年表进行建模。此外，目前公开于国际树轮数据银行（International Tree-Ring Data Bank, ITRDB）的多数树轮年表均采集于20世纪80至90年代，因此我们对美国树木径向生长对土壤湿度敏感性的认知，仅基于经历过多次极端严重干旱的时段，而忽略了近期快速全球变化带来的影响。本研究针对美国俄亥俄河谷这一树轮覆盖稀疏的区域，扩充了其树轮网络。本研究共采用15个树种的72条树轮年表，旨在探究树轮网络密度提升如何影响帕尔默气象干旱指数（Palmer Meteorological Drought Index, PMDI）的重建效果。此外，本研究通过构建截止至1980年的重建序列，并与同一批年表截止至2010年的重建序列进行对比，检验了采样年代（即校准时段）对重建模型的影响。研究结果表明，提升树轮网络密度可使重建值更贴合器测记录的干旱时空变率，对多雨事件的重建效果提升则相对有限。相较于以1980年为截止的校准时段，将校准时段延长至2010年后，研究区域南部的树轮对PMDI的敏感性有所降低——该区域近数十年来并未出现严重干旱事件。本研究强调，构建高密度树轮网络有助于更精准地还原过去干旱与多雨事件的时空变率；此外，国际树轮数据银行中的树轮年表需定期更新，以更好地理解树木径向生长对气候的敏感性随时间的变化规律。