End-of-century projections of North American atmospheric river events in CMIP5 climate models

Most extreme precipitation events that occur along the North American west coast are associated with narrow plumes of above-average water vapor concentration that stretch from the tropics or subtropics to the West Coast. These events generally occur during the wet season (October-March) and are referred to as atmospheric rivers (AR). ARs can cause major river management problems, damage from flooding or landslides, and loss of life. It is expected that anthropogenic global warming could lead to changes in the general circulation of the atmosphere, such as Hadley Cell expansion and jet stream and storm track shifts. Since AR events are associated with cyclonic activity that originates near and propagates along the jet stream, the jet stream configuration influences the frequency and location of AR landfall along the North American west coast. Therefore, it is probable that any changes in the general circulation of the atmosphere will result in changes in the frequency, orientation, and location of AR landfalls. Generally, along the West Coast, CMIP5 models predict increases in integrated water vapor and precipitation, and little change in low-level wind associated with AR events. In this study, CMIP5 RCP 8.5 climate models and high resolution regional climate models are used to analyze predicted changes in frequency and location of AR events impacting the West Coast from the contemporary period (1970-1999) to the end of this century (2070-2099).