Heavy Precipitation over Western North America: Synoptic/Mesoscale Forcing and Decadal Trends

暴雨导致的洪水和滑坡是北美西海岸最严重的天气相关威胁。1980年至2008年间，加州、俄勒冈州和华盛顿州发生了四次洪水灾害，造成的损失超过110亿美元。在俄勒冈州和华盛顿州，与强降水相关的洪水和滑坡导致了总统宣布的大部分灾难，在加利福尼亚州，这一比例接近四分之一。知识价值：虽然在过去十年中对西海岸强降水事件的性质已经有了大量的了解，但在它们的前因、区域和大尺度气象环境、必要条件以及频率或强度的趋势等方面，主要的科学问题仍然悬而未决。这些相互关联的问题将在本次调查中加以考虑。该项目的具体目标包括：(1)确定北加州至加拿大边境地区强降水事件的气候学及其时空特征；(2)确定与强降水事件相关的大尺度和区域条件；(3)确定大降水事件期间来流特征；(4)评估西海岸强降水高分辨率预报的真实性，并确定哪种模式物理模拟最准确；(5)通过诊断高分辨率模拟确定与这些事件相关的详细大气演变；(6)建立过去60年强降水事件的历史趋势；(7)利用全球气候模式强迫的高分辨率区域模拟，确定该地区下个世纪强降水的未来趋势。该项目的智力价值在于它对西海岸强降水事件的特征进行了独特的、全面的和协同的研究，包括它们的气候学、与它们开始相关的条件、相关的大尺度和区域尺度气象结构、模式正确模拟这些事件的能力、过去强降水频率的趋势以及基于气候模式输出的未来趋势。这项工作将解决有关这一重要气象现象的一些重大科学问题。更广泛的影响：本项目调查的科学问题影响气象和水文界对即将到来的强降水事件提供及时和准确预警的能力。这项研究还为基础设施和区域规划提供了必要的信息，从而造福社会。另一个与社会重要性相关的问题涉及西海岸强降水的过去趋势，以及这些趋势在人为的全球变暖下将如何变化。最后，这项研究将为全球其他中纬度地形降水较多的地区提供有价值的信息。

Flooding and slope failures due to heavy precipitation are the most serious weather-related threats for the west coast of North America. Between 1980 and 2008, four flooding disasters in California, Oregon, and Washington caused losses of more than eleven billion dollars. Flooding and slope failures associated with heavy precipitation have produced a majority of presidential disaster declarations in Oregon and Washington, and nearly a quarter of such declarations in California.Intellectual merit:Although a great deal has been learned during the last decade about the nature of West Coast heavy precipitation events, major scientific questions are still outstanding regarding their antecedents, regional and large-scale meteorological environments, necessary conditions, and trends in frequency or intensity. These interrelated questions will be considered in this investigation. The specific objectives of the project include: (1) determining the climatology of heavy precipitation events for the region from northern California to the Canadian border, as well as their temporal and spatial characteristics, (2) identifying the large-scale and regional conditions associated with such events, (3) determining the characteristics of the incoming flow during major precipitation events, (4) evaluating the realism of high-resolution forecasts of heavy West Coast precipitation and determining which model physics produces the most accurate simulations, (5) determining the detailed atmospheric evolutions associated with these events by diagnosing the high-resolution simulations, (6) establishing the historical trends of heavy precipitation events over the past 60 years, and (7) determining the future trends of heavy precipitation over the region for the next century by using high-resolution regional simulations forced by global climate models.The intellectual merit of the project lies in its unique, comprehensive, and synergistic examination of the characteristics of West Coast heavy precipitation events, ranging from their climatology, the conditions associated with their initiation, associated large and regional scale meteorological structures, the ability of models to properly simulate these events, past trends in heavy precipitation frequency, and future trends based on climate model output. The work will resolve a number of major scientific questions about this important meteorological phenomenon.Broader impacts: The scientific issues investigated in this project impact the ability of the meteorological and hydrological communities to provide timely and accurate warnings of upcoming heavy precipitation events. The research also benefits society by providing necessary information for infrastructure and regional planning. Another issue relevant to societal importance deals with past trends in West Coast heavy precipitation and how these trends will change under anthropogenic global warming. Finally, this research should lead to information of value in other parts of the globe where heavy midlatitude orographic precipitation is significant.