ENSO-driven multi-decadal climate variability in Auckland: a Southern Hemisphere coastal city perspective

Coastal cities in Southern Hemisphere mid-latitudes face climate risks from interacting tropical and polar atmospheric systems. This study examines multi-decadal climate variability in Auckland (37°S), New Zealand’s largest city, using 1963–2022 records. Morlet wavelet analysis and robust trend tests identified significant warming in maximum temperature (+0.307°C per decade). After detrending, winter rainfall showed El Niño–Southern Oscillation (ENSO)-related interannual variability, with wet and dry anomalies across phases. Wavelet spectra revealed 28–30-year oscillations consistent with Pacific Decadal Oscillation cycles and emerging 4–6-year ENSO-scale precipitation variability after 2000. Major anomalies coincided with positive Southern Annular Mode phases in 1994–95, when drought occurred, and with the extreme 1982–83 and 1997–98 El Niño events, when local temperature anomalies were 0.23°C greater than during ENSO-neutral and transition years. By contrast, 2010–11 was unusually wet, consistent with enhanced north-easterly flow. Rising humidity (+0.107 hPa per decade) and sunshine duration (+39.32 h per decade) may intensify urban heat stress. These findings demonstrate combined effects of large-scale ocean–atmosphere variability and long-term warming, supporting climate-resilient infrastructure, early-warning systems and urban planning in Southern Hemisphere coastal cities.