Doctoral Dissertation Research: Advances in the Methodologies and Implications for Hydrologic Responses to Climate Change in the Upper Colorado Watershed, UT and CO

大量证据表明，科罗拉多州下游流域地表水文学的变异性与厄尔尼诺-南方涛动(ENSO)之间的关系。有一条证据--古洪水记录--说明了极端洪水对厄尔尼诺事件频率的依赖。在科罗拉多分水岭上游，这些气候异常与ENSO不是正相关，在某些情况下是负相关。在这一地区没有关于古洪水的研究，所以导致极端洪水的水文气候机制是基于时间上有限的、有记录的。这项研究的主要目标是通过编制多洛雷斯分水岭流域尺度的古洪水年表来解决空间差距，以了解极端洪水如何对气候变化做出反应。分水岭包括科罗拉多州西南部和中西部的大片地区，然后流入犹他州摩押附近的科罗拉多河。它是与ENSO关联非常弱的区域的一部分，因此它对气候变化的反应可能类似于上科罗拉多分水岭的大部分地区。这项研究将重点放在地质年代学上，以创建非常可靠的洪水年代学。用“光激发发光法”(OSL)测年古洪水水文的有效性存在疑问。本研究将为OSL在古洪水水文学中的应用提供分析评价。此外，这项研究旨在通过调查冲积地层来评估河道稳定性，以评估古流量估计的不确定性程度。洪峰流量估计将使用一维水文模型完成。这项研究的结果将提供更全面的了解洪水状况对科罗拉多流域上游气候变化的响应。对过去气候变化的水文反应可能是现代和未来对全球变暖的水文反应的合理类比。此外，多种年龄控制和现场技术的结合将减少古洪水研究的不确定性。之所以选择多洛雷斯分水岭进行这项研究，是因为它的独特位置：在一个河流流量与厄尔尼诺事件相关性很差的气候区域，使其成为科罗拉多州上游分水岭内其他子流域的原型。流域的地形对本研究来说是理想的，因为河流既有基岩又有冲积河道，古洪水证据的保存潜力很高。该地区的古洪水记录表明，曾发生过多次极端洪水，每一次都大大超过了历史上的最大洪水。水资源管理者可以应用这些信息来减轻未来洪水的直接影响，特别是在现代和未来气候变化的背景下。

Numerous lines of evidence have highlighted the relationship between the variability of surface hydrology and the El Niño-Southern Oscillation (ENSO) within the lower Colorado Watershed. One line of evidence, the paleoflood record, illustrates the dependence of extreme flooding on the frequency of El Niño events. Within the upper Colorado Watershed, these climatic aberrations are not positively correlated with ENSO, and in some cases, inversely correlated. There are no paleoflood studies in this region, so the hydroclimatic mechanisms responsible for driving extreme flooding is based on temporally limited, gaged records. The primary goal of this research is to address the spatial gap by developing a watershed-scale, paleoflood chronology in the Dolores Watershed to understand how extreme flooding has responded to shifts in climate. The watershed encompasses a broad region of southwestern and west-central Colorado, before draining into the Colorado River near Moab, UT. It is part of the region that correlates very weakly with ENSO, so its response to climate shifts may act as an analog to the majority of the Upper Colorado Watershed. This research places an emphasis on geochronology to create a very robust flood chronology. There are questions about the validity of using "optically stimulated luminescence" (OSL) methods for dating paleoflood hydrology. This research will provide an analytical assessment of OSL for its application to paleoflood hydrology. In addition, this study is designed to evaluate the degree of uncertainty in paleodischarge estimations by investigating the alluvial stratigraphy to assess channel stability. Peak discharge estimates will be completed with a one-dimensional hydrological model.Results from this research will provide a more thorough understanding of flood regime responses to climate change in the upper Colorado Watershed. Hydrological responses to past climate shifts are a potentially reasonable analog for modern and future hydrologic responses to global warming. In addition, the integration of multiple age-control and field techniques will reduce uncertainty in paleoflood research. The Dolores Watershed has been selected for this study because of its unique position: in a climatic region where stream flow is very poorly correlated with El Niño events, making it a prototype for other sub-basins within the upper Colorado Watershed. The physiography of the watershed is ideal for this study because the rivers are mixed with both bedrock and alluvial channels, and the preservation potential for paleoflood evidence is high. The paleoflood record in this region indicates that numerous extreme floods have occurred, each of which greatly exceeds the maximum flood during historical times. Water managers may apply this information to mitigate the direct impacts of future flooding, especially in the context of modern and future climate change.