Doctoral Dissertation Research: A Diatom and Tree-Ring Record of Drought During Medieval Times in the Upper Colorado River Basin

美国西部的关键水资源来自科罗拉多河上游流域，该流域在过去八年中的供水低于平均水平。这场干旱是不是很不寻常？它能持续多久呢？气温上升会加剧这一问题吗？近几个月来，随着研究人员预测美国西部将变得更加温暖和干燥，这些问题变得更加重要。这项研究将通过研究中世纪暖期(MWP；约公元900年-公元1100年)上科罗拉多河流域(犹他州Uinta Mountain)部分地区干旱的持续时间和严重程度来提供一些答案，如树木年轮和湖泊沉积物记录所示。MWP是气温维持在目前预测的人为变暖水平的最近一次间隔。确定MWP期间Uinta山脉供应的水的变化对于该地区未来的水资源管理规划以及美国西部气候模拟和干旱管理等更大的问题至关重要。由于影响美国西部气候的蒸发、季节性降水和海洋表面温度变化的复杂相互作用，目前对这一关键水源地急剧、持续的变暖对水供应的影响知之甚少。特别是，乌伊塔山脉是一个有问题的地区，因为它们位于太平洋海洋表面温度变化造成的水文变化的行动中心之间。这项新工作将增加已经在进行的博士论文研究，该研究正在利用树木年轮(年度分辨率)和过去约13,000年来利用湖泊沉积物岩芯中的硅藻(对环境变化敏感的藻类)的化石遗骸(百年分辨率)来获取关于乌伊塔山过去800年的干旱和干旱的知识。这项额外的研究将把树轮记录进一步扩展到更早的时间，以包括MWP，并将以更高的时间分辨率检查最近的硅藻记录，再次捕获MWP。这里描述的工作是第一次联合树轮和高分辨率硅藻研究乌伊塔地区的干旱。这种双管齐下的研究方法比单一方法研究更有效，因为它允许结果得到独立确认。这项研究还将为美国西部山间地区开发第一个基于硅藻的干旱模型。作为确定Uinta山脉古干旱模式的唯一工作机构，这项研究将有助于了解科罗拉多河流域范围的干旱以及区域缺水问题。考虑到美国西部持续多年的干旱，并预测随着全球气温继续上升，该地区的干旱将加剧，对MWP期间干旱情况的分析非常及时。这项研究的更广泛影响包括为水资源和土地管理者提供用于未来资源规划的基本知识，与其他研究人员共享数据以开发更全面的科罗拉多河流域干旱记录，社区干旱教育，以及为本科生提供研究机会。

The Western U.S. derives critical water resources from the upper Colorado River Basin, which has produced below average water supplies over the past eight years. Is this drought unusual? How long can it be expected to last? Will rising temperatures exacerbate the problem? These questions have gained renewed importance in recent months as researchers forecast warmer and drier conditions in the Western U.S. This study will provide some answers by examining the duration and severity of drought in part of the Upper Colorado River Basin (Uinta Mountains, Utah) during the Medieval Warm Period (MWP; ca. A.D. 900- A.D. 1100) as captured in tree-ring and lake sediment records. The MWP was the most recent interval during which temperatures were sustained at levels now forecast to occur from anthropogenic warming. Identifying the variability of water supplied by the Uinta Mountains during the MWP is critical for future water management planning in the region and for larger issues of climate modeling and drought management in the Western U.S. The impacts of dramatic, prolonged warming on water supplies in this key water source region are presently poorly understood because of the complex interactions of changes in evaporation, seasonal precipitation, and ocean surface temperatures which impact western US climate. In particular, the Uinta Mountains are a problematic area as they lie between the centers of action for hydrological changes caused by Pacific sea surface temperature shifts. This new work will add to doctoral dissertation research already underway that is obtaining knowledge of drought and aridity in the Uinta Mountains over the past 800 years using tree-rings (annual resolution) and over the past ~13,000 years using the fossil remains of diatoms (algae sensitive to environmental changes) in a lake sediment core (centennial resolution). This additional research will extend the tree-ring record further back in time to include the MWP and will examine the recent diatom record at higher temporal resolution, again capturing the MWP. The work described here is the first joint tree-ring and high-resolution diatom study of drought in the Uinta region. This two-pronged research approach is more effective than single-method studies because it allows results to be independently confirmed. This research will also develop the first diatom-based drought model for the intermontane region of the western United States. As the sole body of work identifying paleo-drought patterns in the Uinta Mountains, this study will contribute essential knowledge for understanding basin-wide drought in the Colorado River as well as regional water shortages. An analysis of drought conditions during the MWP is very timely considering the continuing multi-year drought in the Western United States and predictions for increased aridity in the region as global temperatures continue to rise. Broader impacts of this research include providing essential knowledge to water and land managers for future resource planning, sharing data with other researchers to develop more comprehensive drought records for the Colorado River Basin, community drought education, and providing undergraduate student research opportunities.