Changes in Winter Atmospheric Rivers along the North American West Coast in CMIP5 Climate Models

Abstract

Most extreme precipitation events that occur along the North American west coast are associated with winter atmospheric river (AR) events. Global climate models have sufficient resolution to simulate synoptic features associated with AR events, such as high values of vertically integrated water vapor transport (IVT) approaching the coast. From phase 5 of the Coupled Model Intercomparison Project (CMIP5), 10 simulations are used to identify changes in ARs impacting the west coast of North America between historical (1970–99) and end-of-century (2070–99) runs, using representative concentration pathway (RCP) 8.5. The most extreme ARs are identified in both time periods by the 99th percentile of IVT days along a north–south transect offshore of the coast. Integrated water vapor (IWV) and IVT are predicted to increase, while lower-tropospheric winds change little. Winter mean precipitation along the west coast increases by 11%–18% [from 4% to 6% (°C)−1], while precipitation on extreme IVT days increases by 15%–39% [from 5% to 19% (°C)−1]. The frequency of IVT days above the historical 99th percentile threshold increases as much as 290% by the end of this century.

Evaluation of the moisture sources in two extreme landfalling atmospheric river events using an Eulerian WRF tracers tool

“…The relationship between ARs and flood events has been extensively analyzed for the US West Coast region (e.g., Higgins et al, 2000;Ralph et al, 2005Ralph et al, , 2006Ralph et al, , 2004Ralph et al, , 2013Bao et al, 2006;Neiman et al, 2008a, b;Leung and Qian, 2009;Dettinger, 2011;Dettinger et al, 2011;Warner et al, 2012Warner et al, , 2014Rutz et al, 2013;Kim et al, 2013), Europe (Lavers et al, 2011(Lavers et al, , 2012Villarini, 2013, 2014;Ramos et al, 2015Ramos et al, , 2016Eiras-Barca et al, 2016;Brands et al, 2016) and other regions world-wide (e.g., Mahoney et al, 2016;Mundhenk et al, 2016). It is important to better understand the physical mechanisms leading to extreme flooding associated with ARs, considering their impacts on human and natural systems and the mounting evidence that ARs are projected to become more frequent and intense in the future (e.g., Dettinger, 2011;Payne and Magnusdottir, 2015).…”

Diagnosing links between atmospheric moisture and extreme daily precipitation over the UK

“…Over middle latitude regions, atmospheric rivers (ARs), narrow bands of strong moisture transport within the warm sector of extra-tropical cyclones (Browning and Pardoe, 1973;Zhu and Newell, 1998;Dacre et al, 2014;Gimeno et al, 2014), have been linked with heavy rainfall and high river flows in the winter half year (Ralph et al, 2006;Dettinger et al, 2011;Lavers et al, 2011;Neiman et al, 2013). The strength of these synoptic features is anticipated to grow as temperatures rise due to concurrent increases in atmospheric moisture (Dettinger et al, 2011;Lavers et al, 2013;Warner et al, 2015).…”

Atmospheric River Tracking Method Intercomparison Project (ARTMIP): Project Goals and Experimental Design

“…Lavers et al, 2013;Payne and Magnusdottir, 2015;Warner et al, 2015;Gao et al, 2016;Kiehl, 25 2016b, Ramos et al, 2016b). However, there is a lack of systematic comparison of the results Geosci.…”

“…These different methods have strengths and weaknesses, affecting the resultant AR climatologies and the attribution of high-impact weather and climate 15 events to ARs. Their differences are of particular interest to researchers using reanalysis products to understand the initiation and evolution of ARs and their moisture sources (e.g., Dacre et al, 2015, Ramos et al, 2016aRyoo et al, 2015, Payne andMagnusdottir, 2016), to assess weather and subseasonal-to-seasonal (S2S) forecast skill of ARs and AR-induced precipitation (Jankov et al, 2009;Kim et al, 2013;Wick et al, 2013a;Lavers et al, 2014;20 Nayak et al, 2014 ;DeFlorio et al, 2017a, DeFlorio et al, 2017bBaggett et al 2017,), evaluate global weather and climate model simulation fidelity of ARs , investigate how a warmer or different climate is expected to change AR frequency, duration, and intensity (e.g., Lavers et al, 2013;Gao et al, 2015;Payne and Magnusdottir, 2015;Warner et al, 2015;Shields and Kiehl, 2016 a/b;Ramos et al, 2016b;Lora et al 25 Geosci. Model Dev.…”