Hydrometeorology of Flash Flooding Processes and Frequencies in the Northeastern United States

山洪灾害是造成经济损失和人员伤亡最严重的天气灾害之一。 研究表明，在我们目前的气候变化趋势中，高强度降雨将更加频繁，这似乎意味着山洪暴发也将变得更加频繁。 然而，由于洪水是气象和水文过程复杂相互作用的结果，山洪暴发的真实趋势并不明显。 山洪暴发是降雨时空分布与前期土壤湿度和流域尺度水文变量相结合的结果。 我们最近的工作表明，在美国东北部的暴雨径流往往是总降雨量积累（饱和过剩）的产品，而不是高瞬时降雨率（霍顿径流）的产品。 在这个项目中，我们将评估这是否是真的径流，特别是通过探索的基本过程，大气过程与地表水文过程的美国东北部的主要研究问题是：（Q1）是东北部的山洪暴发生产风暴事件有很大的不同，已为中西部和东南部的特点？(Q2)东北部的山洪暴发更经常是饱和过剩或霍顿风暴径流过程的结果？我们已经确定了186山洪事件从2003年至2007年整个美国东北部，我们将使用我们的样本集。 与前几年相比，这一时期雷达数据的差距较小，并且这一时期洪水事件相对较高的频率可能是本世纪预期气候条件下的典型情况。 将通过对与这些暴洪事件相关的风暴事件的天气尺度（1000 s km）和中尺度（10- 100 s km）结构的特征观测，以及基于雷达（根据条件需要使用标准或热带反射率-降雨量关系）和地面站（点尺度）数据的流域尺度降雨量和强度，来处理Q1。 这些数据将与已公布的关于中西部和东南部暴洪风暴的信息进行比较，这些信息比东北部的信息更丰富。由于分布式水文信息，如土壤湿度没有被广泛测量，以解决Q2，我们将估计此信息与合奏的四个流域模型，从完全分布式/完全机械的半分布式/经验，已与区域水文观测流量和土壤湿度。 我们将使用偏差校正的NEXRAD降雨数据来运行我们的流域模型。 一旦我们？知道吗？我们的先决条件（从我们的流域模型结果）和山洪造成的降雨（从第一季度），我们可以使用二元概率分析，以确定流域湿度和降雨量的重合概率需要产生山洪。 通过分析山洪暴发的雨强产生霍顿径流的频率，即，超过土壤渗透能力，这是土壤水分的函数，我们可以确定山洪暴发的频率是多少？霍顿 我们将使用不同的机制和经验的基础，以括号中我们的结果的四个流域模型的合奏，注意：这种方法是因为有什么样的方法，机制与经验，提供了共识？最好的？结果.这项工作将促进大气科学家和水文科学家之间有意义的合作，以帮助将气候变化预测置于它们可能如何影响洪水频率的背景下。 结果将与国家气象局预报办公室共享，理想情况下会产生更及时和空间精确的山洪警报。 研究生将进行大部分的研究，有助于他们作为科学家的培训。 我们正在设计一个新生写作课程围绕社会科学政策的相互作用，在全球气候变化的背景下，使用山洪的水文气象学作为一个一致的主题或案例研究，并将开发课程模块，将本研究的结果和工具纳入其他科学和工程课程。

Project AbstractFlash flooding is one of the costliest weather hazards, both in economic losses and in human casualties. Research showing that high intensity rainfall will be more frequent in our current trend of climate change seems to imply that flash flooding will also become more frequent. However, because flooding results from complex interactions of meteorological and hydrological processes, it is not obvious what will be the true trends in flash flooding. It is well established that flash flooding results from the combination of the spatio-temporal distribution of rainfall with antecedent soil moisture and basin-scale hydrological variables. Our recent work suggests that storm runoff in the northeastern US is more often a product of total rainfall accumulation (saturation excess) rather than a product of high instantaneous rainfall rates (Hortonian runoff). In this project we will evaluate whether this is true for runoff that contributes specifically to flash floods by exploring the fundamental processes that link the atmospheric processes with surface-hydrological processes for the northeast U.S. The primary research questions are:(Q1) Are northeastern flash-flood-producing storm events substantially different from those that have been characterized for the midwest and southeast? (Q2) Are northeastern flash floods more often the result of saturation excess or Hortonian storm runoff processes?We have identified 186 flash flood events from 2003-2007 throughout the northeastern U.S that we will use as our sample set. There are fewer gaps in the radar data during this period than in previous years and the relatively high frequency of flooding events during this period may be typical under climatic conditions expected during this century. Q1 will be addressed by characterizing observations of both synoptic-scale (1000s km) and mesoscale (10-100s km) structures of storm events associated with these flash flood events, as well as the resultant watershed-scale rainfall amounts and intensities based on radar (using standard or tropical reflectivity-rainfall relationships as conditions warrant) and ground station (point-scale) data. These data will be compared with published information about flash flood storms in the Midwest and Southeast, which is more plentiful than that for the Northeast. Because distributed hydrologic information like soil moisture is not widely measured, to address Q2, we will estimate this information with an ensemble of four watershed models ranging from fully distributed/fully mechanistic to semi-distributed/empirical that have been well vetted with regional hydrologic observations of both discharge and soil moisture. We will use bias-corrected NEXRAD rainfall data to run our watershed models. Once we ?know? our antecedent conditions (from our watershed model results) and the flash-flood-causing rainfall (from Q1), we can use bivariate probability analysis to determine the probability of the coincidence of watershed wetness and rainfall needed to produce a flash flood. By analyzing how often flash-flood-generating rain intensities produce Hortonian runoff, i.e., exceed soil infiltration capacity, which is a function of soil moisture, we can determine how frequently flash floods are ?Hortonian.? We will use an ensemble of four watershed models with different mechanistic and empirical underpinnings in order to bracket our results; note: this approach is taken because there is little consensus about which approach, mechanistic vs empirical, provides the ?best? result. This work will foster meaningful collaboration between atmospheric and hydrologic scientists to help put climate change predictions in context as to how they are likely to influence flood frequency. Results will be shared with National Weather Service Forecast Offices ideally resulting in more timely and spatially precise flash flood warnings. Graduate students will conduct much of the research, contributing to their training as scientists. We are designing a Freshman Writing course around society-science-policy interactions in the context of global climate change that uses the hydrometeorology of flash flooding as a consistent theme or case study, and will develop course modules to incorporate the findings and tools from this study into other science and engineering courses.