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

University Of Washington, Seattle WA

Investigators

Abstract

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.