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，过去8年来，该流域的供水量低于平均水平。这次干旱不寻常吗？预计会持续多久？气温上升会加剧这个问题吗？最近几个月，随着研究人员预测美国西部将出现更温暖、更干燥的情况，这些问题变得更加重要。这项研究将通过检查中世纪温暖期（MWP；约公元900年至1100年）树木年轮和湖泊沉积物记录中记录的科罗拉多河上游流域（犹他州尤塔山脉）部分地区干旱的持续时间和严重程度，提供一些答案。MWP是温度维持在目前预测人为变暖所造成的水平上的最近间隔。在MWP期间，确定乌塔山脉供水的可变性对于该地区未来的水资源管理规划以及美国西部气候模型和干旱管理的更大问题至关重要。由于蒸发、季节性降水、气候变化和气候变化之间复杂的相互作用，目前人们对这一关键水源地区持续变暖的影响知之甚少。以及影响美国西部气候的海洋表面温度。尤因塔山脉位于太平洋海面温度变化引起的水文变化的活动中心之间，是一个有问题的地区。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）和湖泊沉积物核心中硅藻（对环境变化敏感的藻类）的化石遗骸（百年分辨率）来获取过去800年来乌干达山脉干旱和干旱的知识。这项额外的研究将把树木年轮记录进一步扩展到包括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。这里描述的工作是首次联合树木年轮和高分辨率硅藻研究在乌干达地区的干旱。这种双管齐下的研究方法比单一方法的研究更有效，因为它允许结果得到独立的证实。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。作为确定温塔山脉古干旱模式的唯一工作，这项研究将为理解科罗拉多河流域的干旱以及区域水资源短缺提供必要的知识。考虑到美国西部持续多年的干旱，以及随着全球气温持续上升该地区干旱加剧的预测，对MWP期间干旱状况的分析是非常及时的。这项研究的广泛影响包括为水资源和土地管理者提供必要的知识，为未来的资源规划，与其他研究人员共享数据，为科罗拉多河流域开发更全面的干旱记录，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.