Collaborative Research: P2C2--Medieval to Modern Climate Variability and Climate Change in the Great Plains

研究的总体目标是利用大平原内或附近的杜松、松树和紫杉树的古老种群，建立对水分敏感的树木年轮年表，用于季节性降水和长期土壤水分平衡的原位重建，这些重建将共同构成大平原干旱地图集（GPDA）。将以0.5度分辨率开发跨越大平原的五个网格重建，包括春夏季的标准化降水指数（SPI），春夏季的降水总量以及夏季帕尔默干旱严重程度指数（PDSI）。重建将以最大长度设计，目标是将湿度估计延长到中世纪时期，那时气候似乎更加温暖和干燥。GPDA将用于检验有关大平原干旱和雨洪的强度、大平原近期湿度趋势的人为印记以及过去500至1000年间大平原上快速发生的春夏骤旱频率的可能的几十年代际机制的假设。美国最高的农业产量出现在大平原地区，该地区也经常遭受干旱，包括2012年的突发性干旱，造成300亿美元的损失。代用树木年轮和湖泊沉积物数据表明，降水和土壤湿度的仪器记录可能不能代表过去一千年来严重干旱和长湿润间隔的自然变率。人为气候变化可能导致北部平原更加潮湿，南部平原更加干燥，这可能是许多气候模式预测的哈德利环流扩张和急流减弱所导致的干燥症状的一种表现。这些人为引起的变化有可能破坏农业、能源生产和水的利用，并且可能因仪器和古气候记录中观测到的周期性年代际极端湿度而被放大。在几乎没有树木的大平原上，很少有确切的年轮年表。数据的缺乏给该地区现有的湿度异常重建增加了相当大的不确定性。该项目旨在通过在大平原及其边界内开发长年轮年表来减少不确定性，以帮助重建这个关键农业地区过去的干旱和潮湿。潜在的更广泛影响（bi）包括对影响美国最高农业产量的大平原地区干旱和极端事件的气候过程的理解。重要的是，该项目包括来自与受影响的农业和部落社区有密切联系的地区初级本科院校（PUI）的研究人员和学生。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The general goal of the research is to develop moisture sensitive tree-ring chronologies from old-growth populations of Juniperus, Pinus, and Taxodium trees from within or near the Great Plains for in situ reconstructions of seasonal precipitation and the long-term soil moisture balance that together will constitute the Great Plains Drought Atlas (GPDA). Five gridded reconstructions that span the Great Plains at 0.5 degree resolution will be developed, including the Standardized Precipitation Index (SPI) for the spring and summer seasons, precipitation totals for spring and summer, and the summer Palmer Drought Severity Index (PDSI). The reconstructions will be designed for maximum length, with the goal of extending the moisture estimates into the Medieval Period when the climate appears to have been much warmer and drier. The GPDA will be used to test hypotheses concerning the magnitude of Great Plains drought and pluvial, the anthropogenic imprint on recent moisture trends in the Great Plains, and the possible multi-decadal regimes in the frequency of rapid-onset spring to summer flash drought over the Great Plains during the past 500- to 1000-years.The highest agricultural production in the United States occurs in the Great Plains, a region also subject to frequent drought, including the flash drought of 2012 that resulted in $30 billion in losses. Proxy tree ring and lake sediment data suggest that the instrumental record of precipitation and soil moisture may not be representative of the natural variability of severe droughts and prolonged wet intervals over the past millennium. Anthropogenic climate change may be contributing to wetter conditions in the Northern Plains and increasing dryness over the Southern Plains, a possible expression of the drying symptomatic of the expansion of the Hadley Cell and the weakening of the jet stream predicted by many climate models. These human-induced changes threaten to disrupt agriculture, energy production, and water use, and may be magnified by recurrent decadal moisture extremes witnessed in instrumental and paleoclimate records. Very few exactly dated, annual tree-ring chronologies are available from the mostly treeless Great Plains. The lack of data adds considerable uncertainty to the available reconstructions of moisture anomalies for this region. This project seeks to reduce the uncertainty by developing long tree-ring chronologies within and along the boundaries of the Great Plains to aid reconstruction of past drought and wetness in this critical agricultural region.The potential Broader Impacts (B.I.) include improvement in understanding climate processes involving drought and extreme events in the Great Plains regions that impact the highest agricultural production in the United States. Importantly, the project includes researchers and students from a regional Primarily Undergraduate Institution (PUI) which has strong ties to affected agricultural and tribal communities.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.