Uncertainties in Projecting Future Changes in Atmospheric Rivers and Their Impacts on Heavy Precipitation over Europe

Abstract

This study investigates the North Atlantic atmospheric rivers (ARs) making landfall over western Europe in the present and future climate from the multimodel ensemble of phase 5 of the Coupled Model Intercomparison Project (CMIP5). Overall, CMIP5 captures the seasonal and spatial variations of historical landfalling AR days, with the large intermodel variability strongly correlated with the intermodel spread of historical near-surface westerly jet position. Under representative concentration pathway 8.5 (RCP8.5), AR frequency is projected to increase significantly by the end of this century, with 127%–275% increase at peak AR frequency regions (45°–55°N). While thermodynamics plays a dominant role in the future increase of ARs, wind changes associated with the midlatitude jet shifts also significantly contribute to AR changes, resulting in dipole change patterns in all seasons. In the North Atlantic, the model-projected jet shifts are strongly correlated with the simulated historical jet position. As models exhibit predominantly equatorward biases in the historical jet position, the large poleward jet shifts reduce AR days south of the historical mean jet position through the dynamical connections between the jet positions and AR days. Using the observed historical jet position as an emergent constraint, dynamical effects further increase future AR days over the equatorward flank above the increases from thermodynamical effects. Compared to the present, both total and extreme precipitation induced by ARs in the future contribute more to the seasonal mean and extreme precipitation, primarily because of the increase in AR frequency. While AR precipitation intensity generally increases more relative to the increase in integrated vapor transport, AR extreme precipitation intensity increases much less.

Atmospheric rivers in 20 year weather and climate simulations: A multimodel, global evaluation

“…The relationship is somewhat consistent with the sensitivity experiments in Hagos et al [], although they found that the sensitivity of AR frequency to model resolution was notable only in the southeastern Pacific. Biases in landfalling AR frequencies in the west coasts of North America and Europe have been largely attributed to biases in the near‐surface subtropical jet locations [ Gao et al , , ]. Biases in AR zonal IVT are, in general, stronger than those in meridional IVT (Figures and ; note different scales between the two figures).…”

“…The importance of ARs in weather and climate has prompted increasing interests on the behavior of ARs in future climate [ Dettinger , ; Lavers et al , ; Payne and Magnusdottir , ; Warner et al , ; Radić et al , ; Gao et al , , ; Hagos et al , ; Ramos et al , ; Shields and Kiehl , , ]. A number of these studies involved, to different extents of comprehensiveness, the evaluation of model performance in simulating the behavior of ARs in the current climate, in order to establish credibility for the model projections.…”

Atmospheric River Impacts on Greenland Ice Sheet Surface Mass Balance

“…While we maintain the >85th IVT PR threshold common to prior studies (e.g., Gao et al, ; Guan & Waliser, ; Nayak et al, ; Payne & Magnusdottir, ), we alter other criteria to account for potential differences in high‐latitude AR characteristics compared to typical midlatitude AR study regions. Because a few studies (Gorodetskaya et al, ; Guan & Waliser, ) have determined a relatively low IVT threshold is needed to reliably detect ARs in polar regions, we fix the minimum raw IVT value for potential AR identification at 150 kg m −1 s −1 rather than the value of 250 kg m −1 s −1 common in midlatitude AR studies (e.g., Rivera et al, ; Rutz et al, ).…”

Future Changes of Subseasonal Precipitation Variability in North America During Winter Under Global Warming

“…Precipitation variability, manifesting in swing between extreme floods and droughts, poses significant risks to human lives, environment, society and properties, and challenges water management (e.g., Cayan et al, 1999;IPCC, 2012;Ralph et al, 2006;Warner et al, 2012). For example, an increase in extreme heavy rainfall under global warming has been reported widely in the literature (e.g., Gao et al, 2016;O'Gorman, 2015;Pendergrass & Gerber, 2016;Swain et al, 2018). For example, an increase in extreme heavy rainfall under global warming has been reported widely in the literature (e.g., Gao et al, 2016;O'Gorman, 2015;Pendergrass & Gerber, 2016;Swain et al, 2018).…”