NSF/EAR-BSF - Extreme Floods in Arid/Semi-Arid Watersheds: Paired Studies in Israel and the US

极端洪水在干旱/半干旱地区具有重大的社会和环境影响。然而，这些极端洪水在这些干旱地区很少发生。由于它们是罕见的事件，因此了解这些洪水的根本原因并确定防止不利影响的方法是一项挑战。在这项研究中，将考察美国西南部和以色列不同流域的洪水响应，并比较两个研究地区的极端洪水特性。在两个不同的地理环境中检查不同的流域，将使研究人员能够更好地了解干旱/半干旱地区控制极端洪水的物理机制。这项研究的结果将对包括应急管理办公室、区域规划方案和洪水预报办公室在内的广泛用户产生重大影响。美国西南部和以色列洪峰的上尾部将通过经验和数值模拟研究相结合，并通过开发和实施降雨和洪水频率分析的新的随机方法来进行研究。研究活动将集中于对这两个研究地区约50个流域的极端洪水进行分析。分析的中心将是应用高分辨率雷达观测来检查美国西南部和以色列对流降雨在时间和空间上的变异性。本研究的主要问题是：1)干旱/半干旱流域的极端洪水响应如何依赖于降雨率的时空变异性？2)干旱/半干旱地区极端致洪暴雨的风暴结构和演变特征是什么？它们是否因暴雨和流域类型而异？3)干旱/半干旱地区在极端降雨和洪水模式方面的特征是什么？4)干旱/半干旱地区的极端洪水是否与不同的洪水产生机制的“混合”有关？5)干旱/半干旱流域降雨和洪水强度的上尾的“性质”是什么？

Extreme floods have significant societal and environmental impacts in arid/semi-arid regions. However, these extreme floods occur only rarely in these dry areas. Because they are rare events, it is a challenge to understand the root causes for these floods and to determine ways to prevent adverse impacts. In this study, flood response in a different watersheds in the Southwestern US and Israel will be examined and properties of extreme floods in the two study regions will be compared. Examining different watersheds in two geographically distinct settings will allow the investigators to better understand the physical mechanisms controlling extreme floods in arid/semi-arid regions. Results obtained from this research will be of significant interest to a wide range of users, including emergency management offices, regional planning programs and flood forecasting offices. The upper tail of flood peaks for the Southwestern United States and Israel will be examined through a combination of empirical and numerical modeling studies and through development and implementation of new stochastic methods for rainfall and flood frequency analysis. The research activities will center on analyses of extreme floods from approximately 50 watersheds in the two study regions. Central to the analyses will be the application of high-resolution radar observations to examine rainfall variability in time and space for convective rainfall in the Southwestern US and Israel. The principal questions that will be addressed in this study are: 1) How does extreme flood response in arid/semi-arid watersheds depend on temporal and spatial variability of rainfall rate? 2) What are the characteristic patterns of storm structure and evolution for extreme flood-producing storms in arid/semi-arid regions? Do they vary with storm and watershed type? 3) What are the characteristic features of arid/semi-arid regions in terms of extreme rainfall and flood patterns? 4) Are extreme floods in arid/semi-arid regions associated with distinctive "mixtures" of flood generating mechanisms? 5) What is the "nature" of the upper tail of rainfall and flood magnitudes in arid/semi-arid watersheds?