Patterns and Drivers of Moisture Transport Variability Over Aotearoa/New Zealand and Their Impacts

ABSTRACT Atmospheric moisture transport plays a critical role for precipitation and surface water availability and is often strongly connected to large‐scale patterns of atmospheric circulation variation. This study investigates the dominant spatial patterns of vertically integrated vapour transport (IVT) variability over New Zealand using Empirical Orthogonal Function (EOF) analysis of ERA5 reanalysis data from 1981 to 2020. The first three EOFs explain over 80% of the total IVT variance. These EOFs are closely linked to variation in New Zealand‐scale synoptic weather types and in turn to the relative strength of zonal vs. meridional surface pressure gradients in the broader New Zealand region and position/strength of the subtropical and polar jet streams. At larger spatial scales, moderate strength correlations were detected between the Southern Annular Mode and EOFs 1 and 2, whereas correlations with other modes such as the El Niño‐Southern Oscillation, Indian Ocean Dipole and Zonal Wave 3 were weak. The study also revealed significant correlations between the leading EOFs and precipitation over New Zealand. Specifically, EOF1 showed a negative correlation with precipitation over western and southern regions of the South Island and EOF2 exhibited a positive correlation with precipitation across central New Zealand. Overall, the results add further detail to our understanding of the complex dynamics of atmospheric moisture transport variability over New Zealand, laying a platform for ongoing refinement of our understanding of spatial patterns in IVT and their connections to the wider climate system.