COLLABORATIVE RESEARCH: Comparison of Regional Flood Frequency Responses to Climatic Variability in the Western United States

[9725336]洪水与过去十年至百年尺度的气候变化之间的联系对未来洪水的规模和频率的概率评估具有巨大的意义，特别是与未来区域或全球气候变化的情景有关。本研究将使用古洪水数据来比较美国西部三个水文气候区（西南、西北和西部大盆地）十年至千年尺度的气候变化对河流大洪水的震级和频率的影响。古洪水研究将提供过去个别洪水事件的物理证据，通过对洪水沉积物的地层分析，将每条河流的严重洪水记录延长100年至1000年。先前在西南地区进行的研究以及1997年夏天在俄勒冈州的约翰戴河和内华达州的特拉基河进行的初步实地工作证实，这三个地区的河流都有出色的古洪水记录。美国西南部河流的古洪水年表表明，在过去5000年里，区域气候条件与大洪水发生频率的百年尺度变化之间存在联系。该项目的一个主要目的是确定在现代记录的短时间尺度上，洪水的时间和控制方面的区域差异是否适用于洪水对长期气候变化的区域反应。即使放射性碳测年方法的分辨率相对较低，这种关于洪水水文气候学的广泛的新视角也是可以实现的。在西部区域气候中心副主任兼区域气候学家Kelly Redmond的合作下，将分析现代流量、气象和大气压数据，作为每个地区古洪水的类比，从而帮助理解在每个区域洪水系列中观察到的模式的潜在物理基础。该研究还将利用统计计算机程序的最新改进，将古洪水信息纳入单站点洪水频率分析（由垦务局开发），以及量化和减少古洪水流量模型不确定性的方法（House, 1996）。基于罕见大洪水的规模和频率的真实信息，了解气候与洪水之间的联系，将提高供水管理者预测全球和区域尺度气候现象的区域后果的能力，这是面对不确定的未来气候条件的长期规划中日益重要的组成部分。

9725336 Ely The connection between floods and decadal-to centennial-scale climatic variations in the past has tremendous implications for probability assessments of the magnitude and frequency of future floods, especially in relation to scenarios of future regional or global climate change. This study will use paleoflood data to compare the influence of decadal-to millennial-scale climatic variability on the magnitude and frequency of large floods on rivers in three district hydroclimatic regions of the western U.S: the Southwest, Northwest, and western Great Basin. The paleoflood studies will provide physical evidence of individual flood events in the past, extending the record of severe floods on each river by 100s to 1000s of years through stratigraphic analysis of flood deposits. Previous studies in the Southwest and preliminary field work conducted during the summer of 1997 on the John Day River in Oregon and the Truckee River in Nevada confirm the availability of excellent paleoflood records from rivers in all three regions. Paleoflood chronologies on rivers in the southwestern U.S. indicate a connection between regional climatic conditions and centennial-scale variations in the frequency of large floods over the last 5000 years. A principal aim of this project is to determine whether demonstrated regional differences in the timing and controls on floods at the short time scales of the modern records hold true for the regional responses of floods to longer-term climatic variations. This broad, new perspective on flood hydroclimatology is achievable even with the relatively coarse resolution of radiocarbon dating methods. With the collaboration of Kelly Redmond, Deputy Director and Regional Climatologist for the Western Regional Climate Center, modern discharge, meteorological and atmospheric-pressure data will be analyzed to serve as analogs for the paleofloods in each region and thus aid in understanding the underlying physical bases for the patterns observed in each reg ional flood series. The study will also take advantage of recent refinements in statistical computer programs for incorporating paleoflood information into single-site flood frequency analyses (developed by the Bureau of Reclamation), and methods for the quantification and reduction of paleoflood discharge-modeling uncertainties (House, 1996). Understanding links between climate and floods from the basis of real information on the magnitude and frequency of great, rare floods will improve the ability of water-supply managers to foresee the regional consequences of glodal-and regional-scale climatic phenomena, an increasingly important component of long-term planning in the face of uncertain future climate conditions.