High‐Resolution Climate Change Projections of Atmospheric Rivers Over the South Pacific

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Abstract Atmospheric rivers (ARs) play a critical role in moisture transport across the Southern Hemisphere mid‐latitudes and often produce extreme rainfall events across New Zealand. Here we examine ARs in a new set of high‐resolution (12–30 km) dynamically downscaled simulations from select CMIP6 models. We begin with a historical evaluation of AR properties from this model ensemble followed by future projections under a high emissions scenario. We demonstrate that by end‐of‐century, the maximum integrated vapor transport associated with ARs will robustly increase by as much as in some regions of the South Pacific, and ARs contribute a larger proportion (up to more) of the annual precipitation climatology in certain regions of New Zealand. The spatial structure and seasonality of these changes indicate the role of a poleward shift and intensification of the westerly jet. This is further quantified through a decomposition into dynamic and thermodynamic components. Although the thermodynamic change dominates the increase in AR frequency, the additional positive dynamical change is notable over the mid‐latitudes and southern New Zealand. Separating events using an AR categorization scale shows that higher category (longer duration, more intense) events more than double in frequency, underscoring the increasing role that ARs will play in extreme weather events in the future for this region.

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