Atmospheric rivers drive monthly rainfall availability in New Zealand

Abstract Atmospheric rivers (ARs) are elongated channels of enhanced water vapour transport in midlatitudes and contribute significantly to annual rainfall in northern and western New Zealand. Based on data from 529 rain gauge sites and detected landfalling ARs over New Zealand from 1950 to 2020, this study indicates that the presence of ARs generally leads to normal or wetter months, and a lack of ARs generally leads to dry months in the warm season in northern and western New Zealand. For eastern New Zealand, ARs do not generally dominate monthly rainfall availability in line with annual observations. Results in this study raise the need for continued understanding of the presence or lack of ARs on water resources month to month to provide further guidance on dealing with rising uncertainties in water supply, hydropower generation, and flood control in a changing climate.