NOAA/WDS Paleoclimatology - New York City 472 Year PDSI Reconstruction

Six water emergencies have occurred since 1981 for the New York City region (NYC) despite: 1) its perhumid climate, 2) substantial conservation of water since 1979 and 3) meteorological data showing little severe or extreme drought since 1970. We reconstruct 472 years of moisture availability for the NYC watershed to place these emergencies in long-term hydroclimatic context. Using nested reconstruction techniques, 32 tree-ring chronologies comprised of 12 species account for up to 66.2% of the average May-August Palmer Drought Severity Index. Verification statistics indicate good statistical skill from 1531-2003. The use of multiple tree species, including rarely-used species that can sometimes occur on mesic sites like Liriodendron tulipifera, Betula lenta and Carya spp., seems to aid reconstruction skill. Importantly, the reconstruction captures pluvial events in the instrumental record nearly as well as drought events and is significantly correlated to precipitation over much of the northeastern US. While the mid-1960s drought is a severe drought in the context of the new reconstruction, the region experienced repeated droughts of similar intensity, but greater duration during the 16th and 17th centuries. The full record reveals a trend towards more pluvial conditions since ca 1800 that is accentuated by an unprecedented, 43-year pluvial event that continues through 2011. In the context of the current pluvial, decreasing water usage, but increasing extra-urban pressures, it appears that the water supply system for the greater NYC region could be severely stressed if the current water boom shifts towards hydroclimatic regimes like the 16th and 17th centuries.

自1981年以来，纽约都会区（NYC）已发生6起供水紧急事件，尽管该地区具备以下条件：1）湿润多雨的气候特征，2）自1979年起开展了大规模水资源节约行动，3）气象数据显示1970年以来极少出现严重或极端干旱事件。我们对纽约都会区流域的可获取水分序列进行了472年的重建，以将这些供水紧急事件置于长期水文气候背景下开展分析。本研究采用嵌套重建技术，基于涵盖12个树种的32组树木年轮年表，可解释5月至8月平均帕尔默干旱严重指数（Palmer Drought Severity Index, PDSI）中最高达66.2%的变异。验证统计结果表明，该重建模型在1531年至2003年期间展现出良好的统计效能。选用多种树木树种——包括偶尔生长在中生境（mesic sites）的鹅掌楸（Liriodendron tulipifera）、甜桦（Betula lenta）和山核桃属（Carya spp.）等较少被使用的树种——似乎有助于提升重建模型的性能。值得注意的是，本重建对器测记录中多雨事件的还原效果几乎与干旱事件相当，且与美国东北部大部分地区的降水量显著相关。尽管1960年代中期的干旱在本次重建的背景下属于严重干旱，但该地区在16世纪和17世纪曾经历过强度相当但持续时间更长的多次干旱事件。完整的重建序列显示，自约1800年以来，区域气候呈现向湿润多雨状态转变的趋势，而一场前所未有的、持续至2011年的43年多雨事件进一步加剧了这一趋势。结合当前的多雨气候背景、区域用水量下降但城市外围用水压力持续攀升的现状，倘若当前的供水丰沛期转向16至17世纪的水文气候状态，纽约都会区的供水系统或将面临严重的运行压力。