High-resolution climate change projections of atmospheric rivers over
the South Pacific
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 (12km) dynamically downscaled simulations from select
CMIP6 models. We begin with a historical evaluation of AR properties
from this model ensemble followed by future projections. We demonstrate
that by end-of-century, the maximum integrated vapour transport
associated with ARs will robustly increase by as much as 20% in some
regions of the South Pacific, and ARs contribute a larger proportion (up
to 20% 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. While 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 categorisation 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 in this region.