NOAA/WDS Paleoclimatology - Hughes - Muir Grove - SEGI - ITRDB CA713

The first dendroclimatic reconstruction of May 1 snow water equivalent (SWE) was developed from a Sequoiadendron giganteum regional tree-ring chronology network of 23 sites in central California for the period 90-2012 CE. The reconstruction is based on a significant relationship between May 1 SWE and tree-ring growth and shows climate variability from interannual to intercentennial time scales. A regression-based reconstruction equation explains up to 55% of the variance of SWE for 1940-2012. Split-sample validation supports our use of a reconstruction model based on the full period of reliable observational data (1940-2012). Thresholds for May 1 SWE low (15 percentile) and high (80 percentile) years were selected based on the exploratory scatterplots relationship between observed and reconstructed data for the period 1940-2012. The longest period of consecutive low-SWE years in the reconstruction is 2 years and the frequency of the lowest SWE years is highest during the period 710-809 CE. The longest high-SWE period, defined by consecutive wet years, is 3 years (558-560 CE). SWE and its reconstruction positively correlate with northeastern Pacific sea surface temperatures, the low-frequency variability of which may provide some predictive ability. Ultimately, the instrumental record and reconstruction suggest that unlike other sites in the region, twentieth century SWE variability in these Sequoia groves has remained within historical boundaries and relatively buffered from extremes and severe declines, though this is likely to change in coming decades with potentially negative effects on water availability for these trees.

本研究基于加利福尼亚中部23个站点的巨杉（Sequoiadendron giganteum）区域树轮年表网络，完成了公元90年至2012年期间5月1日雪水当量（snow water equivalent, SWE）的首次树轮气候重建。该重建模型依托5月1日雪水当量与树木径向生长间的显著相关关系，可反映年际至世纪际尺度的气候变率。基于回归的重建方程能够解释1940-2012年时段内雪水当量高达55%的方差变异。分样本验证结果支持我们采用基于完整可靠器测数据时段（1940-2012年）构建的重建模型。研究结合1940-2012年观测与重建数据的探索性散点图关系，确定了5月1日雪水当量的低（15百分位）与高（80百分位）年份阈值。重建序列中连续低雪水当量年的最长持续时长为2年，而公元710-809年期间最低雪水当量年份的出现频率最高。最长高雪水当量时段（由连续湿润年份界定）为3年（公元558-560年）。雪水当量及其重建结果与东北太平洋海表温度呈正相关，其低频变率或可提供一定预测能力。最终，器测记录与重建结果显示：与该区域其他站点不同，这些巨杉林的20世纪雪水当量变率仍处于历史波动边界内，且相对缓冲了极端事件与严重衰减；不过未来数十年间，这一状况或随气候变化发生改变，进而对这些树木的水分供应产生潜在负面影响。